note to users€¦ · advanccments in nailcd connections acknowled~emcnts 1 wouid iike to thank my...
TRANSCRIPT
NOTE TO USERS
This reproduction is the best copy available.
UNNERSrrY OF TORONTO
ADVANCEMENTS IN
NAILED CONNECTIONS
Maura Lecce
A thesis subrniaed in conformity with the requirernents
for the d e p z af Master cû Applied Science,
Graduate Department of Civil Engineering,
University of Toronto
Q Copyright by Maura Lecce 2M) 1
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ADVANCEMENTS IN NAILED CONNECIlONS
b MAURA LECCE
Degree of Master of Appiied Science
Graduate Departma of Civil Engineering
University of Toronto
2001
h v i o u s research on nailed comections has d t e d in the development of design
guidelines for shear, bearing and net section fracture faiiure modes, for both static and fatigue
loading. Since then new Wess steeI powder actuated fasteners (or "naiis") have been
developed. The purpose of this experimentai study was to determine if the existing design
guidelines are vaüd, or requin modification, for the new stainiess steel na&. A total of 21 nailed
comections have ken tested under static I&g and results confirm that current design
guidelines are appiicabie for connections made with new-generation stainiess steel mils.
Furthexmore, a total of 16 fatipe tests have been conducted and the existing fatigue S-N curves
have been modifieci tu accommodate the current experimental data an stainless steel d e d
connections. More research is recpked to develop design guidelines which take bending stresses
into accuunt.
Advanccments in Nailcd Connections Acknowled~emcnts
1 wouid Iike to thank my supervisor, Professor I.A. Packer for his unwavering guidance
and support houghout my studies.
My appreciation goes to al1 the shop personnel and technicians of the Department of Civil
Engineering for al1 their help and technical support.
1 would also Iike to thank M. Mazniiia for assisting me with laboratory testing.
Financial support for this project was provided by the Nanual Sciences and Engineering
Research Council of Canada (NSERC), the Canadian lnstitute of Steel construction*^ "Steel
Structures Education Foundation", the Comité International pour le Développement et I'Etude de
la Construction Tubulaire (CIDECT) and HiIti AG. Financial assistance given by the Civil
Engineering Department of the University of Toronto in the form of a Teaching Assistantship is
greatly appreciated.
My sincere thanks go to Mr. H. Beck of Hilti Corporation, Liechtenstein for supply of the
powder actuated fasteners and for al1 his expertise and immediate attention to any issues
encountered with the nailing process. Furthemore, my appreciation goes CO Adas Tube for
generously donating the structurai steel h m which the specimens were fabricated.
Finaily, 1 would like to extend my appreciation to my family and friends for all their love
and encouragement.
Advanctments in Nailcd Connections Tabie of Contents
TABLE OF CONTENTS
.. ABSTRACT .....e.~o....................~..........H~~~.~~~...e...............e............................... u ... ACKNOWLEDGEMENTS .*.*.w ..o......*...ooooo.oeo.M*.ee*o.t.*o.e.o**..wo*.*oeo**..*eo..*e................. ...*.o.omoo*.ew LU
TABLE OF CONTENTS . . ~ . . . . ~ . . . . . ~ . ~ . . . ~ ~ ~ ~ ~ e o ~ ~ ~ e ~ ~ e ~ ~ W . ~ e e ~ ~ . ~ ~ . ~ ~ ~ - ~ ~ ~ ~ ~ e ~ ~ . . . ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ . ~ ~ ~ ~ e ~ ~ ~ ~ ~ ~ ~ . . . iv ... ...................................................................................................................... LIST OF TABLES wu
LIST OF FTGURES* . . . . . . . . . . . . . . . . . . ~ ~ ~ ~ ~ ~ ~ m . ~ ~ ~ ~ ~ e ~ ~ ~ . . ~ m ~ ~ ~ o œ ~ ~ . . ~ ~ ~ . ~ ~ ~ ~ ~ ~ ~ . ~ ~ w ~ ~ ~ . ~ e . ~ e Y . ~ ~ . ~ .....*............................... x .. .....*........ .........................................*....................*....*............................. NOMENCLATURE ..... m
INTRODUCTION .W." . . e . . . o . . . . . . t . ~ ~ o ~ * o ~ ~ ~ * . o ~ o o ~ e . e o o o ~ ~ a e e ~ ~ . * e ~ ~ ~ w ~ ~ ~ ~ ~ ~ * . * e ~ ~ ~ ~ . .......................................... 1
LITERATURE REVIEW ..*......."..o*..**.......œ~oeeoo~.m~~~~~................*......*.....m...... . 3
......................................................................... ............................................ 2.1 OVERVIEW ,c, 3
........................................................................................................ 2.2 STATIC STRENGTH 3
2.2.1 GENERAL ............................................................................................................... 3
2.2.2 SHEAR BEHAVIOUR ....................................... , ...................................... 3
2.2.3 BEAEtIFG BEHAVIOUR ................................... ................................................... 5
2.2.4 NET SECTION BEHAVIOUR ............ ., ........ ................................ .................. 5
2.2.5 STATIC STRESS-STRAIN BEHAVIOUR ............................................................ 8
......................................................................... 2.3 FATIGUE STRENGTH ......................... .- 8
2.3.1 GENERAL ........................................................................................................... 8
2.3.2 SHEAR FATIGUE STRENGTH ............................................................................. 8
2.3.3 BEARING FATIGUE STRENGTH ............................. ..................................... 9 2.3.4 NET SECTION FATIGUE STRENGTH .................................. ... .......................... 9 2.3.5 NAILED CONNECTIONS vs. BOLTED. RIVETED AND WELDED
................................................................................................... CONNECTIONS 10
2.4 CONSTANT us, VARIABLE AMPLITUDE L O A D I N G 1 L
2.4.1 GENERAL .................................. ... .................................................................. II
............................................. 2.4.2 MINER'S RULE FOR CUMULATIVE DAMAGE 12
2.4.3 SUITABIUTY OF MINER'S RüLE FOR FATIGUE LIFE EVALUATION ..... 12
2 J OTHER STRENGTH CONCERNS WITH NAILED CONNECTIONS ........................ 14 2.5. I BASE METAL DEFORMATION AND BUCKLING STRENGTH .................... 14
2.5.2 FASTENER TOOL SEITINGS AND PULLOUT STRENGTH ......................... 14 EXPERIMENTAL m S T I G A T I O N " ....-.*...ooo.-**-w****.m*******w**a****m* . - w * w w 24
3.1 GENERAL ...............................,..................................... ................................................ 24
3.2 MATERIAL PROPERTIES ...................-..... .., .............................................................. 24
Advanctments in Nailed Connections T i t e of Contentr
3.2. I TUBE PROPERTIES ......... ................................................................ ................. 24
3.2.1.1 Geometric Properties of Tubes ................................................................. 24
3.2.1.2 Mechanicd Properties of Tubes ................................................................ 24
3.2.2 PLATE PROPERTES .................................. ,,., ................................................. 25
3.2.2.1 Geometric Properties of Plates ................................................................... 26
3.2.2.2 Mechanicd Properties of Plates ............................................................... 26
3.2.3 HILTI X-CR20 DPlOv STAINLESS STEEL NAIL PROPERTIES ..............TI....,. 26
3.2.3.1 Generd ....................................................................................................... 26
3.2.3.2 Geometric froperties ............................................................................. 26
3.2.3.3 Mechanical Pmperties ................................................................................ 26 3.3 SPECIhIEN FABRICATION ........................................................................................... 27
3.3.1 GENERAL ............................................................................................................ 27
3.3.2 CONFECTION DETAILS ................................................................................ 27
3.3.2.1 Tu bular Connections ............................................................................. 27
... ........... 3.3.2.2 Plate Connections ....................... .... , 27
3.3.3 NPJLING OF TUBE AND PLATE CONNECITONS ......................................... 27
3.3.3.1 General ..................................................................................................... 27
3.3.3.2 DX750 Fastening System Settings ............................................................. 28
3.4 TEST PROCEDURES ...................................................................................................... 28
3.4.1 N S E S T ................................................................................. 2 8
3.4.2 NAIL ROCKWJXL HARDNESS TESTS ............................................................ 29
3.4.3 SPECIMEN TESTS ..................................... ,.. ............. 29
3.4.3.1 GENERAL .............................................................................................. 29
3.4.3.2 STATICTESTS ....................................................................................... 30
3.4.3.3 FATIGUETESTS .................................................................................. 30
3+ OBSERVATIONS AND RESULTS oow-oooo~ooe~omooowo~ooooeooooooooeoomoeeooooooeoooooee~omo.oooeeooooooe 44
NAIL S m STRENGTH .............. ..................................... ................................. 44
............................................................................ NAIL ROCKWELL HARDNESS 4 4
STATIC TEST RESULTS .............................................................................................. 4 5
4.3.1 TUBE CONNECTIONS ......................................... .......................................... 45
4.3.1.1 NaiI S hear Failure Mode Tests ................................... ...- ........ 45
4.3.1.2 Bearing Failtire Mode Tests .................................................................... 45
4.3.1.3 Net Section Fracture Faiiure Mode Tests .............................................. 45
4.3.2 PLATECONNECTIONS. .......................... ,., .................................................. 46
Advanccmcnrs in Nailai Connections Table of Contents
4.3.2.1 Naii S hear Failure Mode Tests ................... .. ......................................... 4 6
4.3.2.2 Bearing Failure Mode Tests ....................................... ............................. 47
4.3.2.3 Net Section Fracture Failure Mode Tests ................................................ 47
4.4 FATIGUE TEST RESULTS ................................................................................... 4 7
4.4.1 TUBE CONNECïIONS ............................. .. ............................................... 4 7
4.4.1 . 1 Nail Shear Failure Mode Tests ...................................................... 4 7
4.4.1.2 Bearing Failure Mode Tests ............................................................. 49
4.4.1.3 Net Section Fracture Failure Mode Tests ............................................... 49
4.4.2 PLATE CONNECTIONS .................................................................................... 49
5 . DISCUSSION AND ANALYSIS OF RESULTS ................... .... .....~.~...............~..............e... 77
5.1 STATIC TESTS ............................................................................................................... 77
............................................................................................................. 5.1.1 GENERAL 77
5.1.2 NAIL SHEAR FAILURE ...................................................................................... 77
5.1.3 BEARING FAILURE ............................................................................................ 78
.................................................................................... 5.1.4 NET SECTION FAILURE 79
5.2 FATIGUE TESTS ....................... ....... ............................................................................ 79
5.2.1 GENERAL ............................................................................................................. 79
............................................. 5.2.2 CONCENTEUCALLY LOADED CONNECTIONS 80
5.2.2.1 Connections with X-CR20 DP lOv Nails ................................................. 80
5.2.2.2 Connections with X-CR20 DPlOv and ENPH2-2 IL15 Nails .................. 82
5.2.3 ECCENTRICALLY LOADED CONNECTIONS ................................................ 83 6. CONCLUSIONS AND RECOMMENDATIONS .............................................................. 108
6.1 CONNECTION STATIC RESISTANCE ...................................................................... 108
6.1.1 GENERAL ...................... ...,. .............................................................................. 108
6.1.2 NAIL SHEAR RESISTANCE ........................................................................... 108
6.1.3 BEAIUNG RESISTANCE ................................................................................ 108
6.1.4 NET SECTION RESISTANCE ........................................................................... 109
................................................................... 6.2 CONNECTION FATIGUE RESISTANCE 109
6.2.1 GENERAL ........................................................................................................... 109
6 .2.2 NAIL SHEAR FATIGUE RESISTANCE ...................................................... 110
6.2.3 BEARING FATIGUE RESISTANCE ................................................................. 110
6-24 NET SECTION FATIGUE RESISTANCE ......................................................... 110
Advancemcnts in Nailed Connections Trtbfe of C O ~ C I U S
Advancements in Nailcd Connections List of Tables
Table 2.1 :
Table 2.2:
Table 2.3:
Table 2.4:
Table 3.1 :
Table 3.2:
Table 3.3:
Table 3.4:
Table 3.5:
Table 3.6:
Table 4.1 :
Table 4.2:
Table 4.3:
Table 4.4:
Table 4.5:
Table 5.1 :
Tabie 5.2:
Table 5.3:
Table 5.4:
Table 5.5:
Table 5.6:
Table 5.7:
Table 5.8:
Table 5.9:
Table 5.10:
LIST OF TABLES
Qualitative Evaluation of the Effect of PAFs Compared with other Fastening
Methods (Beck 1997) ............................................................................................. 15
Fatigue Detail for "Base Material with Powder Actuated Fasteners"
.................................................................................. (Niessner and Seeger L999) 15
Po wder Carû-idge Power Levels (HiIti Fastening Technology Manual 1996) ....... 16
Piston Penetration Settings (Hilti Fastening Technology Manual 1996) ............... 16
Geomenic Properties of Tube Material ................................................................. 31
Mechanical Properties of Tube Material (Coupon Tests) ...................................... 32
.............................. Mechanical Properties of Tube Material (S tub Column Tests) 32
Geometnc and Mechanical Properties of Plate Material ........................................ 33
Connection Details of Tube Specimens ................................................................. 34
Connection Details of Plate Specimens ............................................................... 35
.......................................................................................... Nail Shear Test Results 51
Static Test Results of Tube Specimens ................................................................. 52
S tatic Test Results of Ptate Specimens .................................................................. 53
............................................................... Fatigue Test Resulu of Tube Specimens 54
Fatigue Test Resulu of Plate Specimens ............................ ... ................................. 55
Analysis of Static Nail Shear Tests (Tube Specimens) .......................................... 84
Analysis of Static Nail Shear Tests (Plate Specimens) ......................................... 84
Analysis of Static Bearing Tests (Tube Specimens) .............................................. 85
Analysis of Staac Bearing Tests (Plate Specimens) .............................................. 85
Analysis of Static Net Section Tests (Tube Specimens) ............................ .. ...... 86
Analysis of Static Net Section Tests (Plate Specimens) ........................................ 87
Preparation of N o d z e d Data to be Plotted for Tube Connections
failing by the Nail Shearing Failure Mode (XCR nails) ........................................ 88
Preparation of NormaIized Data to be Plotted for Tube Connections
......................................... faiüng by the Tube Bearing Failure Mode (XCR nails) 88
Reparation of Normaiized Data to be Plotted for Tube and Plate
......... Connections failing by the Net Section Fracture Failure Mode (XCR nails) 89
Standard Deviation of S-N Experimental Results Tube Connections
failing by the Nail Shearing Failure Mode (XCR nails) ........................................ 90
Advanccments in Nailed Connections List of Tables
Table 5.11:
Table 5.12:
Table 5.13:
Table 5.14:
Table 5.15:
Table 5.16:
Table 5.17:
Table 5.18:
Standard Deviation of S-N Experimentai Results for Tube Connections
failing by the Tube Bearing Failure Mode (XCR nds ) ........................................ 91
Standard Deviation of S-N Experimental Results for Tube and Plate
Connections failing by the Net Section Fracture Failure Mode (XCR nails) ......... 92
Preparation of Normalized Data to be Plotted for Tube Connections
failing by the NaiI Shearing Failure Mode (XCR and ENPH nails) ...................... 93
Preparation of Normaked Data to be Plotted for for Tube Connections
failing by the Tube Bearing Failure Mode (XCR and ENPH nails) ....................... 94
Preparation of Normaiized Data to be Plotted for Tube and Plate Connections
failing by the Net Section Fracture Failure Mode (XCR and ENPH nails) ........... 95
Standard Deviation of S-N Experimental Results for Bearing Specimens
(XCR and ENPH nails) ......................... t., .......................................................... 96
Standard Deviation of S-N Experimentai Results for Tube and Plate Connections
failing by the Net Section Fracture Failure Mode (XCR and ENPh nails) ........... 97
............................................ Andysis of Eccentrically Loaded Plate Connections 98
Advancements in Nailed Connections List of Figures
Figure 2.1 :
Figure 2.2:
Figure 2.3:
Figure 2.4:
Figure 2.5:
Figure 2.6:
Figure 2.7:
Figure 2.8:
Figure 2.9:
Figure 2.10:
Figure 2.1 1 :
Figure 3.1:
Figure 3.2:
Figure 3.3:
Figure 3.4:
Figure 3.5:
Figure 3.6:
Figure 3.7:
Figure 3.8:
Figure 3.9:
Figure 3.10:
Figure 3.1 1:
Figure 4.1 :
Figue 4.2:
Figure 4.3:
Figure 4.4:
Figure 4.5:
Figure 4.6:
Figure 4.7:
Figure 4.8:
Figure 4.9:
Composite Columns used for the Millennium Tower Roject (Beck 1999) ........... 17
Pushout Test Set-up (Beck 1999) ........................................................................... 17
.................................................. Nail Shear Failwe (Packer and Henderson 1997) 18
"Nipple Dirnple" Effect (Kosteski et ai . 2000) ..................................................... 18
Plate Shear Test Specimens (Beck 2000) ............................................................... 19
Shear Failure. with Bcaring Deformation (Beck 2000) ........................................ 20
Shear Failure. without Bearing Deformation (Beck 2000) .................................. 20
Bearing Failure of T ubular Matenal (Packer and Hendenon 1997) ..................... 21
........................................................... Net Section Fracture (Kosteski et al . 2000) 21
S-N Design Curves and Data Points for Nailed Connections
(Kosteski et al 2000) ............................................................................................. 22
...... Fatigue Design Curves for Nailed . Cdted !üveted and Welded Connections 23
Typical Dimensions of Material Tensile Test Coupons ......................................... 36
............................................................................. Axial Clip Gauge Extensometer 37
Overall Set-up of Tensile Coupon Tests ............................................................. 38
Load vs . Extension Recording Apparatus ............................................................. 38
..................................... Dimensions of Hilti X-CR20 DPlOv Stainless Steel Nail 39
............................................... Nailing Jig for Plate Co~ections (Mazzulla 200 1) 40
................................................................... Double Shear Jig for Nail Shear Tests 41
....................................................................... Overall Set-up for Nail Shear Tests 41
..................................................................... Nail Rockwell Hardness Test Set-up 42
Static Test Set-up for Tube Specimens ......................... .. .................................... 43
Fatigue Test Set-up for Tube Specirnens ............................................................. 43
Single Nail Shear Load vs . Displacement .............................................................. 56
Static Nail Shear Failure Mode (Tube Specimen) ................................................. 57
Static Nail Shear Test Results (Tube Spechnens) .................................................. 58
.................. S tatic Base Metal Bearing Failure Mode (Tube Specimen) ... ....... 59
.................... Staac Bearing Test Results (Tube Specimens) ... ....................... 60 .............. Static Base Metal Net Section Fracture Failure Mode (Tube Specimen) 61
............................... Static Net Section Fracture Test ResuIts (Tube Specimens) 62
................................................ Static Nail Shear Fadure Mode (Plate Specimen) 6 3
.................................................. Static Nail Shear Test Resula (Plate SpMmens) 64
Advancements in Nded Connections tisr of Figures
Figure 4.10
Figure 4.1 1
Figure 4.12:
Figure 4.13:
Figure 4.14:
Figure 4.15:
Figure 4.16:
Figure 4.17:
Figure 4.18:
Figure 4.19:
Figure 4.20:
Figure 4.2 1 :
Figure 4.22:
Figure 5.1 :
Figure 5.2:
Figure 5.3:
Figure 5.4:
Figure 5.5:
Figure 5.6:
Figure 5.7:
Figure 5.8:
Figure 5.9:
Figure 6.1 :
Static Base Metaï Bearing Failure Mode (Plate Specimen) ................................... 65
Static Bearing Test Results (Plate Specimens) ...................................................... 66
Static Base Metal Net Section Fracture Failure Mode (Plate Specimen) ............... 67
Static Net Section Fracture Test Results (Plate Specimens) .................................. 68
Variable Gap Between Tubes Due to Nailing Rocess ........................................... 69
Nail Shear Fatigue Results (Tube Specimens) ...................................................... 70
....................................................... Nail Shear Fatigue Failure (Tube Specimens) 71
.................................. Bearing Fatigue Failwe (Tube Specimen) .., ..................... 72
....................................................... Net Section Fatigue Failure (Tube Specimen) 73
GrossNet Section Fatigue Failure (Lapped Plate Specirnen: With Bending) ....... 74
Net Section Fatigue Failure (Single Plate Specimen: Without Bending) .............. 74
Lapped Plate Connection Fatigue Test with Bending (Mauulla 2001) ................ 75
Influence of Bending on Fatigue Life of Nailed Connections ............................... 76
Normalized Fatigue Data (XCR mils) .................................................................. 99
Determining the Best-Fit Line of Normdized Data (XCR nails) ........................ 100
Mcan Best-Fit Lines and (Mean -2"Standard Deviations) Lines
(XCR nails) ...................................... .. ......... LOI
Normdized Fatigue Data (XCR and ENPH nails) ............................................... 102
Determining the Best-Fit Lines of Nomalized Data
(XCR and ENPH nails) ........................................................................................ 103
Mean Best-Fit Lines and (Mean -2*Standard Deviations) Lines
(XCR and ENPH nails) ............................... ,., .................................................. 104
Cornparison of Fatigue Design Curves ....................................... , 105
Determining Eccentricity for Lapped Plate Connection ................................... 106
Adjusted Stress Ranges for Lapped Plate Connections ........................................ 107
Recommendations for Fatigue Design ....................... ... ................................. 112
Advancements in Nailed Conneztions NornencIuture
NOMENCLATURE
A
Abr
A,
A m
An
A,
A m
&
AASHTO
AISC
ASTM
AREA
AWS
Br
Bu
C
CSA
CISC
cov
d
d'
dn
d m
Area
Bearing area
Gross cross sectional area
Measured area
Norninal area
Net cross sectional area
Normalized area
Shear area
American Association of S tate Highway and Transportation Officiais
American Institute of S tee1 Construction
American Society for Testing and Materials
American Railway Engineering Association
Arnerican Welding Society
Bearing resistance [force]
Ultimate bearing strength [force]
Intercept value
Canadian Standards Association
Canadian Institute of Steel Construction
Coefficient of Variation
Diameter of a fastener
Effective hole diameter
Nominai diameter
Measured machineci diameter
xii
Advancements in Naiied Connections Nomenclancre
End distance, measured from the centreline of a fastener to the fkee end of the
material; Eccentricity
Young's Modulus of Elasticity
Ultimate strength of a materiai [stress]
Yield strength of a materid [stress]
Measured maximum strength [stress]
Gauge or pitch
b e r diameter, Identification
Linearly Varying Differential Transformer
Slope of the S-N curve
Miner's surn, M = EL, where ni = number of cycles that take place at stress i Ni
range level i, and Ni = number of cycles that would cause failure at stress range
level i; Bending moment
Total number of nails
Nurnber of nails per row (r)
Number of cycles
Actual or experirnentally observed number of cycles
Number of cycles of a comection subject to bearing failure
Characteristic number of cycles (used to describe FAT lines)
Final number of cycles
Number of cycles of a comection subject to net section fracture
Predicted number of cycles
Number of cycles of a connection subject to nail shear failure
Outer diameter
Axial load [force]
Advancements in Nded Connections Nomenclature
Powder actuated fastener, used interchangeably with "naii"
Load range [force] = P,, - P,
Maximum load [force]
Minimum load [force]
Ultimate load [force]
Number of rows in a nailed connection
Stress ratio
Circurnferentiai spacing of fasteners
Stress range; Elastic section modulus
Stress range based on the nail bearing area for the critical element
Stress range based on the net area for the critical element
Stress range based the on nail shear area
Thickness
Imer tube w d i thickness
Outer tube wall thickness
Tensile resistance [force]
Ultimate tensile strength [force]
Shear resistance of the connection [force]
Ultimate shear strength [forcd
Measured ultimate shear strength [force]
Width
Lirnit States Design resistance factor
Resistance factor for a boit or nail
xiv
Advanccmcnts in Nailai Connections Zntmduction
1 INTRODUCTïON
Nailing involves the use of high strength steel pins which can be driven into steel by a
powered fastening tool. Powder actuated fasteners (PAFs) are primarily used in industry for non-
smctural purposes such as fastening roof decking to steel beams or mechanical equipment to
steel elements (Beck and Engelhardt 2001).
Studies conducted over the recent years (Kosteski et al. 2000), have shown that nails c m
be confidently used as a stnictural connecter, and that the static and fatigue behaviour of nailed
connections are cornparable to traditional bolted or welded connections. Aside from strength
benefits, using nail fasteners as structural connectors offers other advantages. To name a few, the
procedure is fast, requires no extemal electncal power and is easily inspected. Hence, it is ideal
for on site applications. Also, with minimal training, relatively unskilled workers are able to
perform the work. From a project management standpoint, d l of these factors contribute to total
crew productivity and a shortened construction phase. Fwthennore, steel nailing avoids al1 shop
fabrication and field bolting procedures.
These advantages were reaiised through the Millennium Tower project in Vienna. Buiit
in 1998, it is the first large-scale project which used PAR to transfer shear load in composite tube
columns. The tower is fifty five storeys high and was built in eight months. The short
construction time was made possible because of the PAF technology and other construction
advancements (Huber 2001). "In cornparison with conventional solutions like welded in through-
bolts, fin plates or headed studs the nailed shear connection is very cost effective as no welding is
required, which leads to a reduction in fabrication effort and time" (Beck 1999). Another
application of the nailing technology is for nailed, lapped splice connections for electrical
transmission and distribution line poles, as a repiacement for timber and concrete posts (Kosteski
et al. 2000). As well, nails can potentiaiiy be used to fasten steel plates together for structural
repairs, as an alternative to welding or bolting (Mazzulla 2001).
The popularity of this fastening technique is growing, motivating manufacturers to
continuously test and develop new fasteners and new applications for the Fasteners. As such,
ongoing research is required to investigate the behaviour of connections made with newly-
designed nails.
This report examines the behaviour of new generation stainless steel mils, in spliced tube
connections and plate connections. The naiIs used in this particular programme are the X-CR20
DPlOv, produced by HiIti. The aim was to generate the comection failure modes previously
discovered by Krutzler (1994). Kosteski (1996) and Lecce (1999) for nailed tube splice
Advanctmmis in NaiIed Connections Introduction
connections using non-stainless steel nails, namely, shear failure of the nail shank, bearing failure
of the base material and net section faiiure of the base material, under both static and fatigue
loading. The results are examined to determine if current design guidelines for nailed
connections are applicable for stainless steel naiIs, or if modifications need to be made.
Advancemcnts in NaiIcd Connections Literature Review
2.1 OVERVIEW
Over the recent years, research on nailing technology has grown in popularity, rnotivating
studies conducted in Austria, Germany, the United States and Canada As such, the database of
information regaiding the effects of PAFs on structural steel has grown.
The literatwe review presented in this Section sumarises the findings and
recornmendations on nailed connections, plus other information relevant to the experimental
program, This background will aid in the overall understanding of static and fatigue strength of
nailed connections.
2.2 STATIC STRENGTH
2.2.1 GENERAL
k u g h previous research, conducted at the University of Toronto (Knitzler N94;
Kosteski 1996; Lecce 1999), three failure modes have been established for nailed connections
under axial tension. These are: a) shearing of the nail shank, b) bearing of the connected matenal,
and c) net section fracture of the connected material, The failure modes for nailed connections
resemble those of boIted connections, with the likely exception of block tear-out. Block t e a r a t
is dependent on the edge or end distance h m the centre of the fastener to the free edge of the
connected matenal. For bolted connections, the end distance is typically specified CO be greater
than or equal to three times the bolt diameter to prevent t e m u t (CSA 1994). However, because
the typical nail diameter (d) is around 4.5mm, an end distance less than 3d (13.5mm) would be
irnpractical and not easily achieved due to the size of the nailing tool head, so hence this failure
mode has k e n excluded (Kosteski 1996).
2.2.2 SHEAR BEHAVIOUR
PAFs (or nails) were used for the first time as structura1 shear connectors in composite
columns for the Millennium Tower project (Huber 2001). The composite columns consisted of
an outer steel tube, steel reinforcement, a circular solid steel core, and concrete fiii (Beck 1999a).
NaiIs were inserted into the outer tube and centre steel core. The nail shanks of the former and
conical heads of the latter fasteners provided the shear transfer. The steel and nails for the
column are shown in Figure 2-1.
Prior to the construction of the Tower, a number of pushout (shear) tests were carried out
to define application conditions and a design approach that wouid be consequently used in the
Advanctmts in Nailai Connections tirerasun Revicw
Millennium project (Beck 1999a). The tests involved a variety of high strength, smooth, stainless
steel PAFs loadëd in singïe shear between a steertube exterior an& interior concrete core. Figare
2.2 shows a typical test set-up (Beck 1999a). As the concrete core was pushed out of the tubular
section the load-deflection response was recorded to evduate shear strength and ductility.
Results showed that the measured shear strength per nail fmm the composite section was
equal to or greater than the direct shear capacity (Beck 1999a). An enhancement of shear
scrength was also noticed by Krutzler (1994), where a number of snug tube-in-tube nailed
connections were tested and failed in shear. Figure 2.3 shows nail shear failure for those
connections. This was attributed to a phenornenon termed the "Nipple-Dimple" effect (Krutzier
1994) and is created as the nail pierces through the metai. In the case of tube-in-tube steel
connections, as the nad pushes through the first layer (outer tube) the material immediately
surrounding the nail shank is deformed to form a nipple on the inner side of the outer tube. As
the nail proceeds through the inner tube, a dimple is forrned on the outer side of the inner tube
(Packer 1996). This effect is shown in Figure 2.4. The sarne phenornenon explains the results
obtained by Beck (1999a), that is, a r.iople forms between the steel and concrete, thereby creating
a shear area slightly greater than the nominal fastener diameter. 'The secondary strength effect for
tubes of greater wall thickness was more pronounced (Beck 1999a). This is likely due to the fact
that more tube materiai is displaced dwing the nailing process, creating a greater Nipple-Dimple
effect. The pushout tests performed by Beck (1999a) also demonstrated favourable resuits with
respect to ductility, indicating that the fasteners were able to achieve considerable plastic
deformations in bending. Both strength and ductility are favourable attributes in a structurai
connection.
Evaluation of the shear resistance for design purposes has k e n proposed as follows
(Packer and Henderson 1997):
V, = @,*(Shear Strength of ail) ' ...................... -.-...... (2.1)
where 'single shear strength of the nail as determined by laboratory tests
and = 0.67 (adopted fmm CANICSA-S 16-1-94, CSA 1994).
Note that this formula does not account for the Nipple Dimple effect. The amount of added shear
strength due to the Nipple-Dimple effect is dependent on variables such as materiai thickness and
fastener installation settings and thus is not a diable force (Krutzler 1994). Furthemore, it was
suggested that the nail shear strength be independently determined since the shear pmpemes of
nails are aot regulated to either CSA or ASTM cwrent standards.
Advanctmtnts in Nailai Connections Lifer~ttcrc Review
Another important study conducted by Beck (2000) examined the static shear smngth of
plate connections which were subjected to a dynamic preload. This study is of particular interest
because the nails used for the lapped plate connections were the X-CR20 DPlOv nails, the sarne
nails used in the experirnental tests reported herein. The plate connections were placed under
constant amplitude fatigue loading for a prescribed number of cycles (2niiliion) and subsequently
tested under static load. A schematic of the test specirnens is shown in Figure 2.5. The results
showed that the dynamic preloading did not affect the static shear strength of the plate
connections. Also, plates of variable thickness were used for the lapped pIate connections and
Beck (2000) found that connections made with thinner plates exhibiteci a more ductile shear
failure (yielding or slight bearing of the plate matenal was noticed) whereas those made with
thicker plates resulted in a brittle shear failure. Figure 2.6 shows a specimen which failed in a
ductile mmner and the bearing deformation is highlighted. By cornparison, Figure 2.7 shows a
specimen w hich experienced brittle s hear faiIure, without bearing deformation.
2.2.3 BEARING BEHAVIOUR
The bearing behaviour is of particular significance with respect to nailed connections
because of the rielatively small nail diameters. Since the bearing area is srnaIl the bearing stress is
very high, and is likely to govern the connection design, A series of bearing tests wete conducted
(Kosteski 1996) in which the variables included the material thickness (t), the naiI diameter (d),
the ultimate strength of the material (FJ, and the end distance (e), which d l influence the bearing
behaviour. A typical bearing failure is shown in Figure 2.8. The results confirmed that the
current CSA guideline for the bearing resistance of bolted connections can be safely applied to
calculate that of nailed connections; that is (Packer and Henderson 1997):
B, = 3*h*nft*d*F, (adopted from CANKSA-S 16.1-94, CSA 1994). .... ......., (2.2)
where = 0.67
and e 13*d
Kosteski (1996) found that this equation is appropriate for nailed connections without being over
consemative.
2-2.4 NET SECCION BEHAVIOUR
In the United States, the predominant method to fasten roof decking to steel joists is by
the puddle weld technique and there is Linle experience using PAFs (Engelhardt et al. 2000). As
5
Advanccments in Nailai Connections Liremnîre Revitw
such, a study at the University of Texas was conducted to investigate the effects of PAFs on the
net strength of open web steel joists and to compare PAF to the puddle weld technique
(Engelhardt et al. 2000). Ten Ml-scale roof subassernbiies were tested statically to failure under
vertical load and in ail cases, the PAFs did not transfer any load.
"The results showed no difference in joist load capacity whether puddle welds or PAFs
were used to fasten the decking. The use of PAFs produced no detrimental effects on either the
compression capacity of the thin top chord members or on the tension capacity of the thin bottom
chord members of the joists" (Engelhardt et al. 2000).
A follow-up study was aiso carried out to investigate the net section eficiency of steel
coupons with PAFs and to "determine if current specification niles for computing the net area of
tension members with bolt holes couId be applied to members with PAFt (Beck and Engelhardt
2001). The design guidelines for bolted connections presented in both the AISC and CSA
account for the darnage to the surrounding material due to the specific hole making process. For
example, the CSA standard requires that when computing the net section area, the effective hole
diameter. d'. is equai to the nominal bolt diarneter, d, plus an additional amount as follows:
A, = Ag - n*d'*t ............................... (2.3)
where d' = punch diameter + 2mm (hence normally bolt diarneter + 4mm). (2.3a)
.......................... or d' = drill diameter (normally bolt diameter + 2mm) (2.3b)
A, is the gross area, n is the number of bolts. and t is the cross sectional
thickness
Currently, there are no design guidelines for the net area of a nailed connection that
account for the amount of damage caused by the nailing process. There was concern that driving
a PAF hm met m y cause mrm damage to the surmundi~ig base metal than drillhg a hole,
therefore requiring a greater reduction in net section strength than a dnlled hole and this was the
major motivation for the study by Beck and Engeihardt (2001). Their test pmgram consisted of
many parameters. Steel coupons with PAR were tested and compared to steel coupons with
dnlled holes of the same diameter as the PAF. The type, number and layout of fasteners were
also varied. Furthemore, to test if the fusion between the nail shank and steel base material had
provided any significant load bearing capacity, a set of coupons where the PAFs were installed
and then subsequentiy removed were tested.
For each test, the experimental efficiency was compared to the theoretical efficiency,
given by the foUowing equations:
Advancemcnts in Nailai Connections Litemtun Revicw
Expenmental Efficiency = ' " * 100 Ag * F u
"The test results indicate that at every level of theoreticd efficiency considered in this research
program, coupons with PAFs showed higher experimental eficiencies han coupons with driUed
hotes. That is, PAFs had a smaller effect on net section strength than dnlled holes of the same
diameter" (Beck and Engelhardt 200 1).
Such high experirnental net section efficiencies can be attributed to two main factors.
First, material is not removed when a nail is driven into the steel material, but is rather displaced
around the fastener, suggesting that the actual area is greater than the theoretical net area. The
theoretical net area is calculated as the gross area minus the area nf the holes. Second, there is a
localised strain-hardening effect of the surroundhg base metal, thus exhibiting greater strength
around chat area. These observations are consistent with the results of nailed tubular connection
tests conducted by Lecce (1999). Figure 2.9 shows a typical net section fracture of a tubular
connection (Kosteski et al. 2000). Fusion was found to have negligibIe effect on the net section
efficiency. by Beck and Engelhardt (2001).
The recommendation stemming fmm this study by Beck and EngeIhardt (2Or)l) was that
the current AISC specification for the net area of bolted connections is too conservative for nailed
connections. For example, to account for the drilling process, the AISC code requires that the
hole diameter be increased by l.6mm (Beck and Engelhardt 200 l), which is 10% of the smallest
available menic boit diameter (Ml61 and a b u t 44% O£ a large meaic bolt diameter (M36).
However, the diameters of PAFs are srnail, and for a 4Smm diameter fastener, adding 1.6rnm is
equivaient to increasing the diameter size by approxirnately 36%. hence an additional 1.6mm is
too conservative. For the sarne reason, the current CSA guidelines outlined for the net area of
boIted comections would be too conservative for nailed connections. In another related study, it
was suggested rhat ''for static design calculations, a reduction of the cross section of the base
material due to the nail need not be taken into account" (Beck 1997). However, ''to provide a
conservative basis for net section strength caiculations consistent with current specification rules
for boIt holes, it is recomniended that a damage aliowance equal to 10% of the PAF shank
Advanccmcnts in Nailai Connections Litemre Revïew
diameter be used when computing the net area of tension members with PAFs" (Beck and
Engeîlîardt 200r). nienfore. widr refererrce tu Eqnatim (2.3) theyrecommerrded that
d' = 1.1 *d (for PAF-punctured holes) ..... . . . . - . . . . . . . . . . . . . . . . . . . . (2.6)
It should be noted here that previous net section fracture tests using PAR (Lecce 1999)
dernonstrated that using an "effective hole diameter" of d' = I.O*d was adequately conservative
(Kosteski et al. 2000; Lcce 1999). Furthemore, Beck and Engelhardt (2001) themselves even
conciuded that the static net section fracture sangth could be safely estirnated by using an
effective hole diameter euual to the PAF shank diameter.
2.2.5 STATIC STRESS-STRAIN BEHAVIOUR
A study was carried out by Beck (1997) directed at comparing the stress-stmin behaviour
of the structural steel base material containing different fastenen, including PAFs. bolts in cûilled
holes, self-drilling screws and puddle welds.
Overall, the strength and ductility attributes of the PAF fastening method were favourable
over the other techniques. Table 2.1 shows a qualitative evaluation of the test results (Beck
1997). PAFs compared to self driliing screws and bolts were clearly supenor in ternis of ultirnate
tensile and yield strengths as well as ductility. In cornparison with puddle welds, the ultirnate
tensile smngth and saain behaviour of PAFs were infenor. but the yield saength was superior
(Beck 1997).
2 3 FATIGUE STRENGTH
2.3.1 GENERAL
Research has shown that the three failure modes experienced under static loading,
including, shear failure of the nail shank, bearing Mure of the connected material and net section
fracture of the connected material c m also occur under fatigue loading (Kosteski et al. 2000).
Each fatigue failure mode is discussed below and the fatigue behaviour of nailed connections is
compared to that of bolted, riveted, and welded connections.
2.3.2 SHEAR FATIGUE STRENGTH
Shear fatigue failure was examined by Kosteslri et al. (2000). However, due to the
inadequate number of data points a design equation was not developed. Nevertheless, the nail
8
Advancements in Nailed Connections Lircmncrc Rwicw
shear cnterion was not a critical faAure mode since the measured fatigue life of the fastener was
consistently larger than the predicted bearing-fatigue life of the connected materid (Kosteski et
d. 2000). The shear data points are plotted on Figure 2.10.
2.3.3 BEA.RNG FATIGUE STRENGTH
Bearing fatigue behaviour was examined by Kosteski et al. (2000) where a total of I l
tube-in-tube splices were tested. In al1 cases, the nails behaved in a ductile manner, evident by
the nails bending and the failure was characterized by the progressive bearing of the tube material
around the nail shank. The following design equation based on a slope of m=5, was fonnulated
for the progressive bearing failure mode (Kosteski et al. 2000):
The bearing test data (Kosteski 1996) and design curve are plotted in Figure 2.10 (Kosteski et al.
2000). The design curve includes a "safety factor" (whereby the "kt-fit" mean line is snifted
down by two standard deviations) so that it could be readily incorporated into current North
Amencan steel design specifications.
2.3.4 NET SECTION FATIGïfE STRENGTfi
Fatigue tests conducted by Lecce (1999) involved five specimens, of which t h e failed
by net section Fracture and the other two failed prematurely in the gripping region of the testing
machine. Nevertheless, al1 five data points, which are shown on Figure 2.10 (Kosteski et ai.
2000), agree reasonably with design recommendations by Niessner and Seeger (1999), where
over 1100 fatigue tests, consisting of structural steel coupons punctured with nail(s), were subject
to fatigue Ioading. The main ciifference between the ovo sets of expenmenü is that the nails in
the tubular connections (Lecce 1999) were loaded in shear whereas the fasteners inserted into the
coupons (Niessner and Seeger 1999) were not loaded. Nevertheless, since the failure mode of the
coupon base material is similar to that of the net section fracture of the tubular matenal, it is
reasonable to compare the data.
The results of the nailed coupon tests (Niessner and Seeger 1999) were analysed in
accordance with procedures outlined in Eurocode 3 and the recomrnendations are presented in
Table 2.2. The dope, m, of the S-N curve as predetermined in the Eurocode 3 was fixed at either
m=3 or m=5. The characteristic number of stress range cycles, which is used to define the detail
category is 2x106, meaning that the detail has a certain stress range (in MPa) at two million
Advancemcnts in Nailtd Connections Lireruturc Rcview
cycles. The detail category is descnbed as FAT 90/3 (90MPa stress range at & = 2x106, with a
dope of m=3) or FAT 100/5 (100MPa stress range at Nc = 2x106, with a slope of m=5). The
recommended S-N c w e which best fi& the data was given by FAT 90/3 for ~ 4 x 1 0 ~ and FAT
1 ûû/5 for W l x ld. This corresponds to the following eguations (Niessner and Seeger 1999):
FAT90/3 : Log(N,) = Log(1.46~ IO")-~LO~(S,) . ..... ...................... . (2.8a)
FAT 100/5: Log(N,) = ~ o g ( 2 . 0 0 ~ ~ o ' ~ - s L o ~ ( s & ........................ ..... (2.8b)
This bilinear design cuve is shown in Figure 2.10. Niessner and Seeger (1999) also suggest that
the fatigue limit is reached at N = 5x10~.
As described in the Eurocode fatigue detail (see TabIe 2.2), the guidelines proposed by
Niessner and Seeger (1999) are recommended for powder actuated fasteners with diameters from
3.7 to 4.5rnm installed with powder actuated tools and where the base materiai has a thickness
greater than or equai to 6mm. Other requirements include proper fastener installation, that is,
appropriate penetration depth as well as a distance of at l e s t 15mm ktween the axis of the
fastener and the edge of a neighbouring fastener (Niessner and Seeger 1999).
2.3.5 NAILED CONNECTIONS vs. BOLTED, RNETED & WELDED CONNECTIONS
Currently, for structurai applications, there are three weII-known and widely accepted
connection methods, namely, bolting, nveting and welding for which fatigue S-N design curves
have been established. Comparing the fatigue results of the nailed connections to these
alternatives is usehl in developing a guideline for nailed connections. Figure 2.1 1 shows a plot
of the fatigue design curves for nded connections in comparison to various fatigue design curves
for bolted, riveted and welded connections.
As one cm see in Figure 2.1 1, there are two S-N design curves for nailed connections
induding one for progressive bearing failure and the other for net section fracture. The former
failure mode is characterized by progressive beuing of the connected materid paraIIel to the
applied load, whereas the latter failure mode is characterized by fracture of the net section
orthogonal to the appiied load (Kosteski et al. 2000). (Note that for most practical designs
bearing failwe would likely govern)- Thus, there are two distinct failme modes which are critical
for fatigue loading of naiied connections. In comparison, there is only one critical failure mode
for bolted and riveted co~ections, that is, fatigue cracking of the net section orthogonal to the
Ioad (Kosteski et ai. 2000).
Advanamcnts in Nailcd Connections Lizenuure Rrview
The bearing fatigue S-N cuve (Kosteski et al. 2000) show in Figure 2.1 1 lies above ail
other curves shown suggesting that the performance of a nailed connection, where bearing is the
critical failure mode, exceeds that of bolted, riveted and welded connections. On the other hand,
Niessner and Seeger's S-N curve for net section fatigue life of nailed connections (1999) lies
below the S-N curves for bolted connections, and above those for riveted connections. Evidently,
al1 nailed connections are superior to welded connections, in fatigue.
Three different S-N curves for riveted connections are shown in Figure 2.1 1 induding
AASHTO Category D (1994), AREA Category D (1996), and that proposed by Xie et al. (2001).
Note that AREA (1996) offers three alternative design Cumes for riveted connections and the
ciifference between the curves depends on the clamping force of the rivets and the hoie making
process (Kulak 2000). (Kulak (2000) suggested that more research is required to examine the
effects of the hole making process, clamping forces and hole patterns on the fatigue life of nveted
connections). The AREA curve provided in Figure 2.1 1 is for a riveted shear splice with punched
holes and a normal clamping force. Compared to Niessner and Seeger's (1999) curve for nailed
connections, AASHTO Category D for nveted connections is the closest match up to N = I X ~ O ~
cycles, but rnay be too consecvative for lower stress ranges. The S-N curves for nveted
connections, by Xie et al. (2001) and AREA (1996) underestimate the fatigue life of a nailed
connection.
Overall, the welding technique is the most detrimentai to the fatigue life compared to
other fastening methods.
2.4 CONSTANT vs. VARIABLE AMPLITUDE LOADING
2.4.1 GENERAL
All the s W e s reviewed has fa^ on fatigue strengîh of powder acaiated fasteners were
subjected to constant amplitude fafigue loading. However, in a redistic environment, unlike that
offered by controlled, laboratory conditions, the connections would be subjected to variable
amplitude loading. In many texts and design guidelines, the simple and popular Miner's d e is
used to account for the cumulative damage induced by variable amplitude loading. However, a
ment study conducted by Agerskov (2000) suggests that random amplitude and constant
amplitude loading produce significaatly different fatigue lives and that the Miner's rule rnay give
unconservative results. Also, another study cooducted by Xie et al. (2001) showed that cycIes
accumulated at a stress range below the fatigue limit may, in some cases, be damaging to the
Advancemtnts in Nailcd Comecn'ons Litcrancm Review
stnicture, but these cycles are disregarded by Miner's sum Miner's d e and highlights of the
studies conducted by Agerskov (2000) and Xie et al. (200 1) are presented in this section.
2.4.2 MINER'S RULE FOR CUMULATIVE DAMAGE
Miner's rule is a linear-based damage theory which assumes that "the damage fraction
that results from any particular stress range level is a linear function of the number of cycles that
takes place at the stress range. The total damage from al1 the stress range leveb that are applied
to the detail is the sum of al1 such occurrences" (Kulak and Gilmor 1998). This is represented by
the following equation:
where ni = number of cycles that take place at stress range levet i,
and Ni = number of cycles that would cause failuse at stress range level i
Note that fracture occurs when M=l (Agerskov 2000).
2.4.3 SUITABILlTY OF MINER'S RULEFOR FATIGUE LIFE EVALUATION
As descnied by Kulak and Gilmor (1998), "the Miner's rule has two major
shortcornings; it does not consider sequence effects and it is independent of the amplitude of the
stress cycles." In relation to the former, Miner's d e has been found to produce reasonable
estimations for the fatigue life of stnictures subjected to block Ioading (Agerskov 2000). (Block
loading is a number of cycles accumulating at particular stress ranges; e.g., a specimen undergoes
a particular loadfcycle history in the fdowing blocks: N d to N=Sûû,ûûû at S=lûûûMPa,
N=500,000 to N=l,ûûû,ûûû at S=SûûMPa and N=l,ûûû,000 to 2,000,000 at S=200MPa). This
type of loading usuaily occurs under controlled, Iaboratory environments, but in reality stnrcnires
are subjected to a stochastic loading due CO trafiTc, wind and waves (Agerskov 2000)-
Conversely, Kulak and Gilmor (1998) explain that the sequence effects and stress ampiitudes
have a smdl influence when residual stresses are high and plasticity is restricted.
The suitability of Miner's rule to evaluate the fatigue life of steel stmctutes inctuding
bridges, offshore structures and chimneys was investigated at the Technical University of
Denmark (Agerskov 2000). A totaI of 520 small scale weided plate specimens and 18 full scale
welded tubular specimens were testeci under variable amplitude loading. Experimental fatigue
lives were compared to theoretical lives, which were evaiuated by fiacture mechanics.
Advancemcnrs in Nailcd Connections Lireratun Rwiew
Both experimental and theoretid test results showed that random amplitude generaily
produced shoner fatigue üves than constant amplitude loading for equivalent stress ranges, which
implies that Miner's sum may give unconservative predictions. The main difference between the
results for constant and variable amplitude loading is related to the crack growth acceleration
effects due to the distribution of high tensile and compressive loads. At tower stress IeveIs,
however, the crack acceleration effects had less significance and in these cases, the Miner's surn
evaluation of the fatigue life was more reasonable (Agenkov 2000).
The recommendations that followed from this study were, "for rather broad-banded types
of random loading, which are by and large equal in tension and compression, a value of the Miner
surn, corresponding to failure, of M=1/3 to 112 should be used (rather than 1.0). For rather
nanow-banded types of random loading, which are pnrnarily in tension, a value of M=0.8 to 1.0
seems appropriate" (Agerskov 2000). The nailed connections tested by Kosteski (1996) and
Lecce (1999), as well as those for this experimental programme, are of the "narrow-banded" type,
since both the minimum and maximum loads lay in the tensile range, plus al1 nailed connections
have been tested under constant amplitude Ioading.
Furthermore, in a study on the fatigue performance of riveted bridge girders (Xie et al.
2001), the inadequacy of Miner's rule to estimate the fatigue life was dso acknowledged. The
study involved riveted connection tests, some of which were subjected to constant amplitude
loading and others to variable amplitude loading. For the latter, stress ranges feI1 below andfor
above the fatigue Iimit. (The fatigue limit is the value of stress below which the number of cycles
can, theoretically, increase infinitely without causing failure to the structure). According to
Miner's sum, cycles that accumulate at a stress level below the fatigue Lirnit are disregarded, and
as long as al1 the stress ranges lie below this lirnit, the structure would theoretically remain
undamaged. However, "if some cycles exceed the fatigue h i t , it is assumed that those cycles
p~oduce chnage and that the cycles ttiat are beiaw the fatigue limit can then inmase the damage"
(Xie et ai. 2001). Unlike codes available in North America (AASHTO, CSA), the UK Code,
BS5400, takes this into account by adjusting the slope of the S-N curve, thereby extending the
curve beyond the fatigue Iimit and lowering the stress Limit (Xie et d. 200 1).
For future experiments on nailed connections, it may be worthwhile to consider broad
banded, variable amplitude fatigue loading and compare with data collected on constant
amplitude loading. Furthermore, it may be prudent to examine if cycles accumulated at a stress
range below the fatigue limit do, in fact, exacerbate damage to a structure which has been
subjected to a fatigue stress above the limit.
Advancemcnts in Nailed Connections Lirerature Review
2.5 OTHER STRENGTH CONCERNS WITH NAILED CONNECTIONS
2.5.1 BASE METAL DEFORMATION AND BUCKLING STRENGTH
Due to the nature of the PAF installation technique, deformations of the base material are
expected. This, however, nised concerns that the deformations would cause prernature buckling
of the connected material, jeopardising the load carrying capacity (Engelhardt et al. 2000). As
part of an experimental program on the effects of PAFs on the strength of open web steel joists
(Engelhardt et al 2000). particular attention was given as to whether or not deformations due to
installation would induce prernature buckling. Also, if the fasteners do not provide enough
stiffness between the roof decking and joists, laterd torsional buckling of the steel joists may
occur at a lower load, and control the design (Engeihardt et al. 2 0 ) . Ten full scale roof
subassembiies, where PAFs were used to fasten the roof decking to the open web steel joists,
were tested under vertical Ioad, and tests showed that neither local nor lateral tocsional buckling
were limiting failure modes. As such, it was concIuded that the use of PAFs was satisfactory
(Engelhardt et al. 2000).
To avoid unnecessary damage to the base material, PAFs should be used within the
application Iimits recommended by the manufacturer. This is further discussed in the following
subsection.
2.5.2 FASTENER TOOL SETTINGS AND PULLOUT STRENGTH
Consulting the manufacturer's product information guide to select fasteners and to use
them within the recommended application limits is important to ensure a sound connection.
Correct fastener tool settings are essential for adequate penetration, sufficient pullout strength,
and to minirnize damage to the base materiai. Tables 2.3 and 2.4 show a list of the available
camidges and their d a i v e strengrhs and the piston penetration settings built into the RX750
fastening tool, respectively. If the settings are too high the nails may be overdriven and
consequentiy become loose in the connection. If they are too low then the nails may be
underdriven, in which case there is insufficient peneaation suggesting inadequate anchorage.
Penetration depth is dso influenced by the nail properties and base material pmperties. Until a
specific guideline is developed for nailing in steel design codes, consulting the manufacnirer's
product guide, as aforementioned, plus experimenting with triai connections, would iikely ensure
a proper connection.
Table 2.1: Qualitative Evaluation of the Enect of PAR Compared with other Fastening Methods (Beck 1997)
Detaif category
PAFd Bolts (drlUed holes)
>l >I >1
Pbwdsr actuatad fasten- e n with diameten from 3.7 to 4.5 mm insblkd with p a r acttwted piston bob in basa matefialmththiduiess 26 ttun.
PAFd ~ell&iIIhg Serews
>l >1 >1
Attribute
Utimate tensile strength Yidd point
Strain behaviour
Requirements
PAF'S/ Pllddle Welds
cl >1 cl
The datnll utegory 90 with m = 3 or the detail category 100 wia, m = 5 is alterna- üvdy appliibk (tecornmendation: 90, w 3 for N c l û$100, m 5 for N>10').
The appmprhte dapth of penetration of the powder actwted fasteners. is g h n according to the applfcatfon mies of the manufacturer. Wmng hstemr installaüons as popped out or inciinad instalkd fastenen are aovsred. Piston mrlu in t)ie basa mate- rial due to m n g th of the tml without a fiasmer or notc)ies due to fastenen ~ ~ t h . . ~ ~ t a b e rrmowd by appropriate metasures.
A minimum distance of 15 mm between ths usis of the powder achiated fastener and th adge of a neîghbounng nota b raqum.
Table 2.2: Fatigue Detail for "Base Material with Powder Actuated Fasteners" (Niessuer and Seeger 1999)
A d v a n ~ e ~ ~ ~ ~ t s in Nailai Connections Litemtun R a i e u
Yeilow
7 le (Black)
Driving Power 1 Lowes t I
Hinhest 1
Table 2.3: Powder Cartridge Power Levels (Hilti Fastening Technology Manual 1996)
Table 2.4: Piston Penemtion Settings (HiIti Fastening Technology Manuai f 996)
DX750 Tool Penetration Setting
1.0
Penetration
Lowest
Adv;incements in Noilcd Connections Liremure Revient
Figure 3.1: Composite Columns used for the Milienniurn Tower Project (Beck 1999)
Figure 2.2: Pushout Test Set-up (Beck 1999)
Advanccnicnts in Nailed Connections Litetmure Revi'
Figure 3.3: Nail Shear Failure (Packer and Henderson 1997)
Figure 2.4: "Nipple Dimple" Effect (Kosteski et ai. 2000)
Advancements in Nailcd Connections Litemture Reviw
Fisure 2.6: Shear FaiIure, with Bearing Deformation (Beck 2000)
Figure 3.7: Shear Faiiure, without Bearing Deformation (Beck 2000)
Advanccments in NüiIcd Connections Lirerature Revicw
Figure 2.8: Bearing Failure oPTubular Marerial (Packer and Henderson 1997)
Figure 2.9: Net Section Fracture (Kosteski et al. 2000)
Advancemcnts in Nailcd Connections Litcrature Rcview
Advanctmtnts in Nailai Connections Experinaentai Investigation
3 EXPERIMENTAL INVESTIGATION
3.1 GJ3NERA.L
The purpose of this report is to examine the static and fatigue behaviour of nailed, lapped
splice connections, which have k e n targeted towards exploring the failure modes of nail shear,
bearing and net section fracture using new generation stainless steel nails. Consequently the aim
was to deterrnine the applicability of design recommendations generated in the past for these
failure modes, using non-stainless steel nails. Both tube-in-tube splices and Iapped plate
connections have been tested. Static tension tests were first conducted on connections to
determine the elastic range of the load versus displacement graph, the yield load and ultimate load
of the connection, and the failure mode. From the staac test results, appropriate stress ranges
(within the elastic range) were chosen for the fatigue tests.
3.2 MATERIAL PROPERTlES
3.2.1 TUBEPROPERTES
The circular HSS matenal was provided by Atlas Tube Inc. and was produced to either
ASTM A500 (1999) Grade C specifications with a minimum yield stress Fy = 317MPa or to
CANKSA G40.2/G40.21-98 (1998) Grade 50W, Class C specifications with Fy = 345MPa. The
geomeaic and mechanical properties of the tube matenal were collected pnor to fabrication of the
connections, as they are essential for designing the experirnents and for the anaiysis of the results.
3.2.1.1 Geometric Pro~erties of Tubes
The geometric properties include the tube diameter, area and wall thickness. The
diameter and thickness were measured using vernier calipers and the cross-sectional area was
calculated h m knowing the density of steel (7850 kg/m3), by weighing accurately a specific
length of tube and the vernier-measured diameter. Table 3.1 shows the nominal and measured (or
actual) geometric dimensions for the tubes used in these experirnents.
3 21.2 Mechanical Promrties of Tubes
The mechanical properties were collected from tensile coupon tests and stub column
tests. Two coupon tests were conducted for each length of tube (seven lengths of tubing) to
determine the materiai propemes incIuding yield strength, ultimate strength, elongation and
modulus of elasticity. Table 3.2 shows the redts of the coupon tests. Each coupon was cut
longitudinally 90° radially h m the weld seam. Figure 3.1 shows a schematic of a typical
Advanctmtnrs in Nailcd Connections EiIPerimentd Investinorion
coupon. Machined metal shims were used as filler material for the curved coupons to avoid
httcning of the roupon by the of the mr mechine. This detait e m d h t the kat&
pomon remained concentrically loaded. An axial clip gauge extensometer, as shown in Figure
3.2, with a gauge length of 5 0 m , was attached to the coupons during the testing to measure the
load-strain response. Al1 coupons were loaded in a quasi-static manner and the stroke was
controlled according to common procedures established at the University of Toronto Strucnurtl
Testing Faciiities. Figures 3.3 and 3.4 show the overail set-up of the tensile coupon md the Ioad
vs. displacement recording apparatus, nspectively. As the coupon material reached specific
sûain values, the machine stroke was held constant for a short period of time to simulate a tme
static loading condition. At these strain values, where the machine stroke was held constant, dips
in the Load vs. Strain graph occurred, A curve comecting the "dips" in the graph characterises a
mer static loading response. The yield load of the matenal was then determined by the
intersection of this "me static Ioading curve" with a Iine drawn parallel to the initial elastic
loading line but with a 0.002 saain offset. Hence, the ' h e " static yield strength and ultimate
strength were deterrnined (see Figures A.1 to A.7 in Appendix A).
The stub column tests were performed on each tube size (three different tube sizes)
according to the Structurai Stability Research Council (SSRC) procedures outlined for rnetal
structures (Galambos 1998). Stub column tests were carried out to obtain an average stress strain
response over the entire cross section, accounting for the residual stresses and cold forrning.
Table 3.3 shows results of the stub column tests and Figures A.8 to A.10, in Appendix A, show
the stress strain results. Four main gauges were placed at mid-height of each tube, separated at
90°, to mesure the strains and to ensure proper alignment of the specimen in the testing machine.
The required alignment was limited to 0.5% strain difference ( h m the average strain value),
which is measured at 25% and 50% of the expected yield load, to ensure concentric loading.
Four Linearly Varying Differential Transfomers (LVDTs) were also set-up to measm the stress
strain response over the entire Iength of the stub column.
3.2.2 PLATE PROPERTIES
Two plate sizes were used for the plate connection specimens. The plate materiai of
6.35m.cn (1/4") nominal thickness was produced to CSA G40.2144W (1998) specifications with a
minimum specified yield stress Fy = 3û4MPa and the plate material of 3.18mm (118") thickness
was pmduced to ASTM AIOIIIA 1011M-00 Type B (2000) specificatioas with minimum
specified yield strength of Fy = 2OSMPa The plate thickness and strength properties were chosen
purposely to be sirnilar to those of the tube material so that the two test series could be compared.
Advancemcnts in NaiIed Connections Experinaenral Invcsrigation
3.2.2.1 Geornetnc PKJberties
Table 3.4 lists the nominal and measured thicknesses of the steel plates. Measurements
were taken using vernier cdipers.
3.2.2.2 Mechanical Properties
The plate material properties including yield strength, uitimate strength, elongation and
modulus of elasticity were determined by coupon tests, similar to those canied out for the tube
material (see Section 3.2.1.2). Two coupons for each plate were cut, parallet to the direction of
rolling of the material. Since the plate coupons were flat, metal shims (used for tube coupons)
were not needed to keep the load concentric. Table 3.4 shows the plate coupon test results. with
the average value for the two coupons being recorded.
3.2.3 HILTI X-CR20 DPlOv STAINLESS STEEL NAIL PROPERTES
3.2.3.1 General
nie designation "X-CR20 DPlOv" of the stainiess steel nail represents some of the nail
properties. that is "CR" means corrosion resistant nail with a total Iength of 'ZO"mm, "DP"
means double warher configuration and finally "IOv" represents a zinc coating of lOpm
thickness. The X-CRS0 DPlOv nails used in this experimental program are of a particulas
rnanufacturing lot, namely lot number 403 698. The lot number is of significance because the
material propemes may Vary slightly from lot to lot.
3.2.3.2 Geometric h ~ e r t i e s
The most important geometrïc properties of the nail pertaining to this study are the nail
shank diameter and useabIe Iength. The nominal nail diameter is 4.5rnrn and the length below the
head is 20mm. A practical thickness of material that c m be c o ~ e c t e d is approximately L6mrn.
Nail dimensions are shown in Figure 3.5.
3.2.3.3 Mechanical Properties
Hilti X-CR20 DPlOv nails, made h m austenitic stainiess steel, have a corrosion
resistance level quivalent to or better than AIS1 3 16 stainiess steel (Hilti AG 2000). The
reported mean Rockwell C Hardness for the lot of nails used in this experimental program is 50.7
Advanccmcnts in N d e d Connections E r p e h n t a l Investigation
which corresponds to an ultimate tensile strength of 1 7 0 0 ~ ~ a ' . Shear strength and Rockwell C
Hardness tests weie alsu p e r f o d a& the Univessity of Tomta Materials Laboratq Facilities
as part of this experimentd program.
33 S P E C r n FABRICATION
3.3.1 GENERAL
Specimen fabrication and testing took place at the University of Toronto Structural
Testing Facilities. Al1 tube materid was donated by Atlas Tube Inc. and the plate matenal was
purchased from Milliken Steel Sales Ltd. The Hilti DX750 direct fastening system was used to
drive the X-CR20 D P l b nails into the steel materid.
3.3.2 CONNECTIONDETAILS
3.3 -2.1 Tubular Connections
Compatible tubular sections. whereby one tube fi& snugly into another, were chosen for
lapped splice connections. The inside weld beads of the outer tube had to be ground off so chat
the inner tube would fit into the outer tube. The parameters varied in this study were the inner
tube thickness and the number of nails to produce either nail shear failure, bearing failure or net
section fracture. Table 3.5 summarises the tubes connected, connection details and the fastener
tool settings for each test.
3.3.2.2 Plate Connections
Each lapped plate connection consisted of two plates of the same or different thichess.
Al1 plates were cut to a nominal width of 95.25mm (3 W') and plates for the lapped connections
were cut to a nominal length of 457mm (18"). Two of the fatigue specimens consisted of a single
plate with a length of approximately 610mm (24"). These two single plate specimens were tested
to determine the severity of the bending effects observed, specifîcally in the fatigue test
specimens (Mazzulla 2001). The plate connection details are listed in Table 3.6.
3-33 NAILING OF TUBE AND PLATE CONNECTIONS
3.3 -3.1 General
The Hilti DX750 direct fastening system (or nailing gun) was used to drive the X-CR20
DPlOv nails into the steel material. For each comection, a template was used to comctly align
E-mail correspondence h m H, Beck, Hilti AG, June 21,2000.
A dvancemcnts in Nailed Connections berimrnrcrl In vesri~alion
the naiiing gun and hence get the fastener in its correct position. A speciai nailing jig, as shown
in Figue 3.6 wrts erated te facilime 6he ~~GEngprdure of the plate specùriens. G a p ir, the
jig were provided to ailow the nails to exit the base plate. By using the bolts and plates, the
lapped splice remained clamped together during the nailing process. CIamping the plates together
prevented the plates from "jumping apart" during the nailing process, prornoting the favourable
creation of the "Nipple Dimple" effect (Mazzulla 2001).
3.3.3.2 DX750 fast en in^ Svstem Semngs
Two important variables with respect to the DX750 tool settings are the powder booster
cartridge type and the piston penetration setting. Using the appropriate settings is important to
pnvent overdriving or underdriving the nails. if the nail is overcîriven. then the nail could be
loose in the connection, which is especially undesirable under fatigue conditions as vibrations cm
cause the loose nail to fa11 out. If the nail is underdriven it is possible that there is not enough
clamping of the nail, or the fnctional forces are not fulIy deveioped, thus comprornising the
integrity of the connection. Finding the ideal combination of cartridge power and penetration
setting for each different set of connections is necessary to develop adequate pullout strength.
A study provided by Hilti (Beck 1999b) which describes the optimum tool settings for
different co~ec t ion thicknesses and base steel strength was used as a guideline to determine the
appropriate cartridge and penetration settings. For al1 connections, the number 5 (Red) cartridge
was used. The penetration setting depended on the thickness of the connection and for the thicker
connections (combined tube thickness of 10.9mrn, or combined plate thickness of I2.2mm) a
setting of 3.5 was used whereas a setting of 2.0 was used for the thinner connections (combined
tube thickness of 8.2mm or combined plate thickness of 9.0mm).
3 3 TEST PROCEDURES
3.4.1 NAIL SHEAR TESTS
Nail shear tests were performed to assess the material properties of the nails. A special-
purpose double shear jig, as shown in Figure 3.7, which was originally designed for testing the
ENEW2-21L15 nail (Krutzler, 1994), was used to load the naüa Eight nails were machined to a
diameter slightly lower than the nominal diameter (4.5mm) to fit into the jig. A spacer was used
to position the nail in the jig and to ensure that the shear planes intenected the rnachined shank
diameter. A 245kN capacity MTS machine was usai to load the nails, and al1 tests were quasi-
static and stroke contded with a Ioading rate between 3 d m i n and 6 d m i n . The machine
Advancemmts in Nailcd Connections &perùnentai I n v ~ ~ t i g ~ ~ i o n
stroke was taken as the deformation of the nails under shear loading. Figure 3.8 shows the
odfset-apofbnait-nsn.
3.4.2 NAIL ROCKWELL HARDNESS TESTS
Figure 3.9 shows the Rockwell C Hardness test set-up. Originaily, 10, unaltered nails
were tested and a correction factor (ASTM A370 1997) was applied to the HRC readings to take
into account the nails' cylindncai surface, However, when compared with the Hilti-reported
average HRC value (50.7), it was evident that applying a correction factor introduced
inaccuracies. and therefore produced unreliable results. With the advice of ~ e c k ' , the HRC tests
were redone on flattened nails. To do this, 10 nails were machined on two, parallel sides
according to ASTM standards (1997) and four HRC measurements were recorded for each nail,
totalling 40 HRC tests. The test results are explained in Section 5.2.
3.4.3 SPECIMEN TESTS
3.4.3.1 GENERAL
Tube Srnimens
For both static and fatigue tests, a 1000kN capacity MTS Universal Testing Machine was
used to apply concenvic tensile loading. In the past (Kosteski 1996; Lecce 1999), a plug and pin
configuration was used to hold the tube specimen in place in the machine. The plugs were
machined to fit the inner diameters of the connecting sections and the load applied to the plug
was transferred to the specimen through the pin. As the bearing s m s acting on the tube was
high at the location of the pins, the tube ofien needed a collar (welded to the tube) for
reinforcement, to prevent bearing failure at that location. However, this detail offered poor
performance, especially under fatigue loading. Premature failure of the specimen would tend to
occur at the location of the weld (welded collar) or at the pin hole, and as a result, a great amount
of time was spent cepairing the specimens. Therefore, the plug/pin detail was abandoned and a
more simple and effective method of preparing the test specimen for the machine was used.
Sufficient length of materiai was cut to allow the ends of the tubes themselves to be gripped by
the MTS machine. Using V-grips, the MTS was able to accommodate the ends of the inner and
outer tubes. To prevent flattening of the tube material by the grips, soüd plugs were machined to
fit into the tubes.
Lengths of tube were eut between 381mm ( 19') and 457m.m (183. Shorter specimens
allowed for speedier fatigue tests.
E-mail comspondence h m H. Beck Hilti AG. March 28,2001.
Advanccmenrs in Nailui Connections ErperMcnrai Invesrigarion
Plate Specimens
The same IûûûkN capacity MTS Universal Testing Machine used for the tube tests was
used for the plate tests, again to apply static or fatigue tensile load. As described by Mazzulla
(2001) "Due to the inherent eccentricity in a singly lapped plate connection, shims were placed at
both erds of the specimen to achieve a more desirable loading condition." This was done to
minimize the bending in the connection and thereby load the connection predominandy in shear.
The shirns were the same width as the test plates and approximately 200mm (8") in length
(slightly longer than the machine grip Iength).
3.4.3.2 STATIC TESTS
Al1 static tests were quasi-static, strokecontrolled and enabled the post-peak response of
the connection to be measured. For the tube tests, the connection displacement was measured
using two LVDTs, mounted opposite each other, with the connection displacement measured over
a Iength of 200mm. Figure 3.10 displays the static tube test set-up. For the plaie tests, the
connection displacement was rneasured by the stroke of the MTS machine.
3.4.3.3 FATIGUE TESTS
From the results of the static tests, appropriate stress ranges were chosen for the fatigue
tests. That is, al1 Ioad ranges for the fatigue tests lay within the elastic range of the static test*
This was done to prevent yielding of the specimen prior to failure. Al1 fatigue test specimens
were subjected to constant amplitude loading, at a frequency in the range of 3.0 to 7.0 Hertz. In
the case of tube and single-piate specimens, the loading was concencric. However, for the iapped
spiice connections bending of the plates was evident, despite attempts to reduce eccentricity by
the use of shims. The specimens were cycled between a minimum and maximum load, which
were boch within the elastic tensile range. (Hence this stress ratio, R >O). The lower value of the
tensile load was SkN for al1 specimens and the upper value was between 30kN and 165W,
depending on the particular specimen. The typical fdgue set-up for the tube specimens is shown
in Figure 3.1 1.
Notes
Noininal Size
0,D. * t mm*mm -
60,3*3.18 60,3*3,18
Nominiil Area
mm2 - 523 523
1: Dcnsity of Sicd îakcn as 78501cglm3 (CISC 2000)
. . - . . - -. - - - - -
Micrometer 1 Mtxt~urcd Measured O.D. L e n a
2: Calculaied Lhickness and calculriied area used Lhroughout design and andysis
Tüble 3.1 : Geomctric Propcrties of Tube Material
M e a ~ ~ r e d Mass
~ & u ~ ~ Area
Actua1:Nomind Area
Advancemtnts in Nailcd Connections Erperimemal Investigation
I I I 1 Measured Spec i f i Yidd
Specified Steel Minimum Stress Tuk1.D. Size
O.D. * t Grade Yield (02% Stress offset)
2 60.3'3.18 A500GradeC 317 329 3 60.3*6.35 CANKSA SOW 345 389 4 60.3*6.35 CANKSA SOW 345 392
Measured Modulus Uliimate of Measured Stress EIasticity Elongation
TabIe 3.2: Mechanical Roperties of Tube Material (Coupon Tests)
-
Measured Moduhs Maximum of
Stress Elasticity Fm= E
Tube I.D.
Table 3 -3: Mechanical Properties of Tube Material (Stub CoIumn Tests)
Nominal Size
O.D. * t
mm-
Y ield Stress at 0.2% offset
FY MPa
Table 3.4: Gcometric and Mechanical Properties of Plate Material
Nominal Thickness
mm 6.35 (114")
k
3.18 (1/8")
Measurcd Thickness
mm 6.07 '
2.97
Specified Grade
CSA G40.2144W AIOIlA 1011M-00Type B
Spccified Minimum
YieM Strcss
MPa 304 205
Measured Y ield Stress (0.2% offset)
FY
MPa 310 266
Measured Ultimate
Stress
Fu
MPa 461 403
Modulus of Elastici ty
E
MPa 186,800 198,2ûû
Measured Elongation
% 32
I
33
Specirnen I.D.
SS IFS 1 SS2lFS2 SS3JFS3
FS4
Outer Tube
O.D. * t"
~irnensions'
mm*mm
73.0*66.5 73.0*6.35 73.0*6.35 73.0*6.35
Jnner Tube
O,D.* t,
~imensions'
mm*mm P
60.3 '6.35 60.3F6.35 60,3*6.35 60.3'6.35 6O,3*3.18 6O,3*3,18 60,3*3.18 6O,3*3,18 6O,3*3.18 60,3*3.18 60.3". 18 60,3*3.18
Number of Nûils per Row
n r
Connect ion Parameters
Numh;.r of Rows
r
Circurnferentiiil Pitch or Gauge
8
1 DX750 Fastener Tm1 - .
1 Settings
Spacing S
mm
Notes 1 : Nominal Dimensions SSIFS-Static Shenr tesVFatigue Shear test
nii
na na na na na na na na 30
SB/FB=Static Beoring testlFatigue Bearing test
End Distance
C
mm
SNIFN=Static Net Section Fracture tesWatigue Net Section Fracture test
Cnnndgc No.
35 35 35 35 35 35 35 35 35 25
'1 able 3.5: Connection Details of Tube Specimens
5 5 5 5 5 5 5 5 5 5
Penetration Seiting
( Plate Thickness 1 Conncction Parameters 1 13x750 Fastener Settines
Plate I t l
mm 6.07 6.07 6.07
Platc 2 t2
mm - 6.07 6.07
6.07
Confiectioii L C D ~ ~ '
(plate width W
mm - 95.3 95.3 95.3 95.3 953 95.3 93.3 95.3 95.3 7
95.3 95.3 95.3 I
95.3 95.3 - 95.3 95.3
End Distanc
e
mm 35 35 35
- 7 - 7 7
Penctratio~ Setting
- 3.5 3.5 3.5 - 2.0 2.0 2.0 - 2.0 2.0
1 2.0 - 2.0 2.0 2.0
- -
Spacing S
mm
Number O Numbcr of Rows
Row
Specimcn I.D.
- PSS 1 PSS2 PSS3
A pproxirnate Plate length (each plate)
mm 457.0 457.0 457.0
Cartridge No.
- 5 5 5
PSB l PSB2 PSB3 PSBI-A PSB2-A PSB3-A PSN 1 PSN2 PSN3 PPN2 PPN3
Notes 1: Nominnl Dimensions PSS=Plate Static Shenr test PFN=Plate Fatigue Net Section Fracture test
PSB=Plate Static Bearing test PFN-S=Platc Fatigue Net Section Fracture test-Single Plate PSB-A=Plate Static Bearing test (Modified) PSN=Plate Stutic Ner Section Fracrurç test
Table 3.6: Connection Details of Plate Spccirncns
Grip Lçngth = 178 mm L r machineci width = 12.7 mm
width = 25 mm 1 *
Overall Coupon Length = 460 mm t
Figure 3.1 : Typical Dimensions of Material Tensile Test Coupons
Advmcements in Nailcd Connections Erperimenral lnvesrigarion
Figure 3.2: Axial Clip Gauge Extensometer
Advrinctmnts in Nailed Connections Erperimcnral Invesrigarian
Plastic
Head
I 1
I 'a
All dimensions in mm
Figure 3.5: Geometric Properties of the XCR20-DP 10v Nail
Advancements in Nailed Connections Erperimenral lnvcrrigation
Advrmccmenrs in Nailed Connections EXperimenral invesrigarion
Advanccments in NaiIed Connections ErperVlienral Investigation
Figure 3.9: Nail Rockweli Hardness Test Set-up
Advancemenci in Nailcd Connections Ecperimenral Invesrigarton
Advanccmaits in Nailed Connections Observcrrions and Resuits
4 OBSERVATIONS AND RESULTS
4.1 NAIL SHEAR STRENGTH
Eight nails were loaded in double shear using a specid-purpose jig and the average
ultimate shear strength was 171cN (single shear). It is important to note that tfiis value pertains to
the r d nail diameter (4.5mrn), not the smaller machined diarneter used in the tests. The results
for individual nail shear tests are listed in Table 4.1. The coefficient of variation was 0.012,
indicating a slight variation in the test results. This mean single shear strength of 17kN is very
similar to that reported by Beck (2000) on a particular lot of X-CR20 DP lOv fasteners wherein he
found an average of 17.6kN. For shear tests performed by both Beck (2000) and in this study, the
nails were subjected to a very small amount of bending. The single shear load versus nail
deformation plots are shown in Figure 4.1. By cornparison, the ENPH2-21L15 nails used in
previous tests had a shear strength of 21.15kN (Krutzler 1994)- that is 24.4% higher shear
strength than the X-CR20 DPlOv nails.
4.2 NAIL ROCKWELL HARDNESS
As previously described in Section 3.4.2. the original Rockwell C Hardness test results
were adjusted using a correction factor to account for the cylindrical surface of the nails, resulting
in an average KRC of 47. This is 7.3% lower than the Hilti-reported average HRC of 50.7 for the
particular lot of naiIs used in this study. Using a "correction factor", however, produced dubious
results. As such, the same number of nails were tested (four readings per nail) but on a
machined-flat surface resulting in an average HlCC of 49.1, or 3.2% lotver than 50.7. Clearly,
testing a flat surface eliminates much of the error.
Often HRC values are related to the ultimate tensile strength. However, this correlation
is not diable for austenitic stainless steeIs (ASTM A370 1997) such as the X-CR20 DPlOv nails
and thus is not done here. Regardless, X-CR20 DPlOv nails are produced to a minimum tensile
strength of 1850MPa Furthermore, the manufacturer (Hilti) uses HRC rneasurements mainiy to
comlate to application ürnits of the fastener rather than to determine tensile strengthL.
' E-mail correspondence h m H. Beck, Hilti AG. March 28.2001:
Advanccmcnts in Nailai Conndons Observations and Ruulrs
4 3 STATIC TEST RESULTS
4.3.1 TUBE CONNECTlONS
A total of nine static tests were conducted and each specimen failed in the anticipated
failure mode. The results are presented in Table 4.2.
4.3.1.1 Nail Shear Failure Mode Tests
Three specimens failed by shearing of the nails and the= was no bearing failure of the
tubular rnaterial pnor to the nails shearing. Figure 4.2 shows a typical static shear failure and
Figure 4.3 shows the load versus displacement graphs. Evidently the connection experienced
little yielding prior to nail shear failure, hence it was a brittie failure. After shearing of the nails.
the load dropped to a value appmximately 15% to 23% of the ultimate load and then the
connection began to pick up load to as much as 89% of the ultimate load (see Figure 4.3). This
load gain is due to the friction between the interface of the tubes and nail pieces.
4.3.1.2 Bearine; Failure Mode Tests
Three specimens experienced bearing failure of the inner tube material, as shown in
Figure 4.4. Also, as the inner tube material went into bearing, the nails were subject to bending
and ultimately sheared. Note, however, that the principal (or goveming) failure mode was
bearing of the thin walled inner tube. The load venus displacement graphs for the bearing Mure
tests are shown in Figure 4.5. The total connection displacement was expected to equal the end
distance (35mm) but due to slight imperfections with nail alignment dong with a small arnount of
stretching of the thin inner tube (evident by cracking of the mil1 scale), the total connection
displacement was closer to 40mm-
4.3.1.3 Net Section Fracture Failure Mode Tests
The 1st three connections failed by net section fracture dong the first row of nails, as
shown in Figure 4.6. Significant yielding and smching (evident by the cracking of the surface
Ml1 scale) of the inner tube occurred prior to fracture of the net section. Figure 4.7 shows the
load venus displacement graphs for dl three tests. Evidently, as the number of nails per row
increases (or A, decreaxs) the connection displacement also decreases. This can be explained
by the fact that the more nails there are in a connection, the greater the damage is to the material;
that is, the material is already fractured by the nailing operation and there is less rnaterial to be
"stretched" and fractured by the applied load. The diffmnces between the load for each
spccimen are very slight, suggesting that the p s s area cm stiU be used as the net area
Advanctmcnts in Nailed Connections Observan'ons and Resulu
However, to be consemative a net area (gross ami minus the nail "holes") c m be used, as done in
Table 4.2 and previously by Kosteski et al (2000).
4.3.2 PLATE CONNECTIONS
A total of 12 plate connection tests were conducted. Unlike the tubular specimens, the
plate specimens were subjected to an eccentric load, inherent by the lapped configuration of the
plates. As such, the plate connections were subjected to axial load plus bending. The effects of
the bending are discussed below. Table 4.3 shows the static plate test results.
4.3.2.1 Nail S hear Failure Mode Tests
A total of six plate shear tests were conducted. Origindly, only three lapped plate
connections, namely PSSl to PSS3, were predicted to fail in shear, However, three additional
lapped plate connections, namely PB1 to PB3, which were predicted to fail in bearing, actually
failed in shear. This happened because of the bending forces introduced by the lapped
configuration (the prying effects are furcher discussed in Section 5). The predicted and actual
failure loads are provided in Table 4.3 and Figure 4.8 shows a nail shear failure test specimen.
The fmt three shear tests (PSS1 to PSS3) showed no bearing of the connected matenal,
whereas tests PSB 1 to PSB2 showed a slight amount of yielding before failing in nail shear. This
small amount of yieiding, however, did not qualify as bearing failure. The load vs. dispIacement
responses of plate specimens PSS 1-PSS3 and PSB 1-PSB3 are shown in Figure 4.9. Generally,
connections PSSI-PSS3 exhibited brittle behaviour whereas connections PSBI-PSB3
expenenced greater deformation and thus the behaviour was more ductile. Sirnilar results were
found by Beck (2000) where lapped plate tests (of similar thicknesses to those used in this
expenmental study) experienced nail shear Mure under static load. Beck (2000) also observed
slight bending of the nails and damage to the nail heads if yielding (or slight bearing) was
involved. There was no damage to the nail head in this experimentai program, but the
conclusions with respect to the load-displacement behaviour are the same.
For both sets of tests (PSSI-PSS3; PSBl-PSB3), once the maximum load was reached
and the nails sheared there was complete separahon of the plates, This is different to the nail
shear tests of the tube-in-tube specimens, where the confined configuration of the connection
ailowed friction between the outer and inner tube to develop and thus regain load after the nails
sheared.
Advancerntnts in NaiIed Connections Observations Lutd Results
4.3.2-2 Bearine: Failure Mode Tests
Since the original set of bearing-prefictet fainire mode tests actuatry faieà in shear, tRree
of the 3.18mrn (1/8") plates were machined down by approximately Irnm to ensure bearing
failure. Figure 4.10 shows a typical failure mode for tests PSB LA, PSB2-A and PSB3-A, which
involves local yielding of the plate matenal around the nail shank. The material in bearing built
up around the nail shank, which is a classic characteristic of bearing failure, and bending of the
nails was also noticed. Eventually, the nails sheared and the connection was no longer able to
maintain any load, as shown in Figure 4.1 1, but the principal failure mode was bearing. This was
also the trend noticed with the tube bearing-connections.
4.3.2.3 Net Section Fracture Failure Mode Tests
Three net section fracture tests were conducted and the failure path went through the
thinner plate, dong the first line of nails as shown in Figure 4.12. The Ioad vs. displacement
response is plotted in Figure 4.13. Rior to fracture, there was gross yielding of the section near
the nailed portion, and this is consistent with the observations of the tube net section fracture
specimens. Also like the tube specimens. there was litde difference in the maximum loads. once
again suggesting that the gross area can be used as the net area
3.4 FATIGUE TEST RESULTS
4.4.1 TUBE CONNECTIONS
Table 4.4 surnmarises the fatigue test results of the tube specimens and shows how the
normalized areas were cdculated. A total of 12 tube specimens were tested under fatigue loading
and each specimen failed in the anticipated mode with the exception of one test which was
intended for shear failure but actudly failed by net section Cracture, with some damage to the
nails in the connection.
4-4.1.1 Nail Shear Failure Mode Tests
Four fatigue specimens, designated as FS 1, FS2, FS3, and FS4 were predicted to fail by
nail shear fatigue failure mode. With the exception of FS4, al1 tests failed by nail shear.
Specimen FSI experienced a drop in Ioad capacity when two nails on one side of the tube
sheared. It is believed that these specifc nails were also subjected to bending forces, due to the
gap between the inside and outer tube created during the nailing process. That is, as the fmt nail
is driven into the tubes, the driving force of the nailllng gun pushes the imer tube against the outer
Advanccnicnts in Nailcd Connections Observarionr anâ Resulrs
tube (opposite side of the first nail location), creating a variable space between the two tubes.
This effect is shown in Figure 4.14. As a result, the first nails driven into the tube were slighdy
overstressed (due to additional bending under load) and thecefore failure was initiated at that
location. The test was terminated after nail shear failure occurred.
Specimens FS2 and FS3 also experienced nail shear failure, as was evident by a sudden
and significant displacement of the connection. However, the load range was maintained for
nearly the same number of cycles it took to reach shear failure. For example, specimen FS2
expenenced significant connection displacement, or nail shear failure at Ns=47 1,680 but the total
number of cycles before the load dropped was Ne3.670. M e r the nails sheared, the broken
nail pieces "dragged" dong the inner tube matenal and this fiction supported the appüed load for
another 431,990 cycles. (Note that the number of load cycles at this initiai major increase in
displacement is the value recorded in Table 4.4). The number of cycles to shear failure and final
number of cycles are plotted in Figure 4.15. Fatigue cracking of the inner tubular materid
determined the end of the test, at which point the load could no longer be supported. Figure 4.16
shows the connection afier complete failure and one can see the sheand nails, nail-drag marks
and fatigue crack, which developed perpendicular to the direction of the load. Another
observation made was as the specimens reached nail shear failure, outward displacement of some
of the nails in the connection occurred and this can also be seen in Figure 4.16. The movement of
the connection urider fatigue loading may have caused the weakened nails to "pop" out.
One can recall that the static shear failwe tests reached a maximum load, then dropped to
about 15% of that but then the load picked up to as much as 89% of the maximum load, even
though shear failure had already occumd. Again the reason for the load gain was due to the
friction between the inner tube matenal and sheared nail piecw. The only difference with the
fatigue test is that 100% of the load was regained because the maximum applied fatigue load was
set below the maximum static load.
Throughout this study, fatigue failure has been defined as the point at which the
connection cm no longer sustain the load range. However, for this set of tests, nail shear failure
was characterized by a significant slip in the connection rather than a drop in load.
The 1s t specimen FS4, which was intended for nail shear failure actually failed by net
section fracture. However, unlike the typical net section fracture failures where the failure was
solely of the critical connected material, this particular specimen (FS4) also experienced nail
damage on three of the six nails. A "wedge" of nail material located at the tip of the nails was
separated from the remainder of the fastener, thus the chree nails experienced tension failure.
Fusion between the connected matenal and the nails, developed during the nailing process,
Advanctn#nts in Nailtd Connections Observations and Resuits
created tensile forces within the nail. The naiI wedges remained in contact with the tube base
materiai. The other three nails remained intact. Unlike test specimens FS2 and FS3 described
above, FS4 did not undergo a significant slip nor did it maintain any load. rather, it exhibited a
bride failun. Moreover, the fatigue crack, which went through the iine of nails, showed no
evidence of yielding. Specimen FS4 has been analysed together with the other net section
fracture failure test data.
4.4.1.2 Bearing Failure Mode Tests
Five fatigue specimens failed by progressive bearing of the thin, inner tube materid, as
illustrated in Figure 4.17. Sirnilar to the static bearing tests, bending and shearing of the nails
also twk place. By cornparison, the ENPH2-21L15 nails used in Kosteski's bearing tests (1996).
did not shear but rather bent significantly, indicating that the stainless steel nails used in this
experirnental program are more brittle.
4.4.1.3 Net Section Fracture Failure Mode Tests
Four tube-in-tube specimens failed by net section fracture failure mode namely FNI,
FN2, FN3 and FS4. As described in Section 4.4.1.1 above, FS4 was expected to fail by nail shear
but failed by a net section fracture failure mode instead. For al1 specimens, the outer tube
thickness was nomindly 6.34rnm. The nomina1 thickness of the inner tubes used for FNI to FN3
was 3 . 1 8 m and that for FS4 was 6.34m. For d l tests, net section fracture of the inner tube
occurred. Figure 4.18 demonstrates a typicd net section fracture fatigue failure mode
expenenced by FNl, FN2 and FN3. The location of the initia1 fatigue crack is evident by the
variation in find cross sectional area of the inner tube (see Figure 4-18). The thicker portion of
the cross section shows a typical fatigue-fractured surface, whereas the thinner portion indicates
stretching and yielding (similar to static failure) which occurred when the connection could no
longer sustain the Ioad. As aforementioned in Section 4.4.1.1, the inner tube crack of specimen
FS4 showed no yielding. (To be consistent with the identification of net section fracture fatigue
failure tests, FS4 will henceforth be referred to as "FN4").
4.4.2 PLATE CONNECMONS
Table 45 displays the fatigue results of the four plate specimens. Only two of the tests,
namely PFN2 and PFN3 involved a lapped splice connection where a thin plate (118") was
fastened to a thick plate (1/4'*) with two rows of na&. For these tests, signXcant bending was
Advanccmcnts in NaiIcd Connections Observan'om and Results
obsemed and, in both cases, a fatigue crack was initiated just above the first row of naiIs, but
shifted to the centre of the first nail row as the fatigue crack progressed (see Figure 4.19).
The other two specimens, PFlV2-S and PFN3-S were single plates punctured with a single
row of nails. (These tests are similar to those conducted by Niessner and Seeger (1999), where
single coupons were punctured with nails, as described in Section 2). The stress ranges applied to
PFN2-S and PFN3-S were the same as the lapped plate connections PFN2 and PFN3,
respectively. This was done to determine the influence of bending on the fatigue life of the
connection. As bending did not influence the single plate tests, the fatigue crack developed dong
the single line of nails as shown in Figure 4.20. The bending effects are illustrated in Figure 4.21.
A plot of the four data points is provided in Figun 4.22. Clearly bending adversely affects the
fatigue life of a connection.
Test No.
= 1 2 3 4 5 6 7 8 -
Nominal Diameter
4 mm
4.5 4.5 4.5 4.5 4.5 4.5 4.5 4.5 -
Ultimate Single S hear
Strength
v"'"
kN 15.88 15.88 15-50 15.88 16.00 15.50 15.75 15.50 -
Measurcd Machined Diamctcr
Average Measured
Shcar S trcss
V,,'"IA~
MPa
Measured Area
- Single Shew
Scrength *
vu lm 7
17.07 17.23 16.74 17.15 17.28 16.74 17.09 16.90 -
Standard Dcviation
0.208
cov 0.012
- Stroke ai Ultimate
Load
mm 0.57 0.59 0.54 0.6 1 0.59 0.79 0.68 0.69 -
Note: *Single Sliear Strength V u = ~ n ( ~ u m / ~ d ; whcre, An=nominal area (dn=4.5mm)
Table 4.1 : Nüil Shear Test Results
- Aclual Pailuie Load
kN - 186 140 153 - 68 8 1 100
- Ratio of Mual to "dicteci
Loiid
- 1.37 1.37 1.29 1.11 1 .O6 1 ,O9
1.29
1.37
1.47
-
- 7" of nner iube
MPa œ
464 464 464 - 394 394 394 - 394
394
394
-
- A, of inner Tube
mm2 - 1008 1008 1008 518 518 518
- # of Jtrils Per Row
n, - 8 6
7 4 5 6
12
14
16
-
- Outer Tube I,D.
- 6 6 6
- lnner Tube I.D.
- 4 4 4
1
1 1 1 - 1
1
1
-
Failure Mode
I
Vail Shear Y ail Shear Ynil Shear
Nei Section Fracture
b a d 3
kN - 370 394 382 184 179 174
143
133
123
Predictd Bearing Load2
kN - 293 220 257 61 76 92
Predicted Vail Shear
Load '
kN - 136 102 119
nner Tube ihickness
'i
mm - 5.86 5.86 5.86 2.87 2.87 2.87
Bearing Bearing Bearing
Ne1 Section Fracture
Net Section Fracturie
Net Section Fracture
Notes 1: Predictd Shear load based on Vu=17*n, where 17 is ihe single shear strength of a nnil obiained frorn shear tesis, in kN and n is the total number of nails = n.*r 2: Predicted Bearing laad bas& an Bu=3*d*i*n*Fu, adopied fmm CANKSA-S 16.1-94 (CSA 1994) and where n=n,*r 3: Predicied Net Seclian Fracture laad given by T,,=&*F,, adopied h m CANKSA-S16.I-94 (CSA 1994), whcre A, is îhe gross ares minus the
prduct of (number of nails pur row)*(diametcr of nail)*(thickness of crirical plate)
Table 4.2: Static Test Resulis of Tube Specimens
- Plate I ( 1/4")
2ridcal Grass Area
!
m
Test I.D.
PSSI ' PSS2 ' PSS3 ' PSBI ' PSB2
PSB3 ' PSBI-A ' PSB2-A ' PSB3-A '
PSN 1 l
PSN2 l
PSN3 l
Predicicd Jet Sectioi Fracture
b a d 3
kN I
24 3 229 216
# of Nails
Per Row
'4 - 2 3 4 2 3 4 - 2 3 4 - 4
5
6
-
- # of
Rows r
- I 1 1 1
1
1 - 1 1
1 - 2
2
2
-
- hdicted
Nail S hear
Load'
kN
Predicted Failure Load
kN - 34 5 1 68
Actual
P a i l u ~
Losd
kN I
35.5 55.0 69.5
Ratio of
Actual tc
Predictec
Load - 1 .O4 1 .O8 1 .O2
Actual
Failure Mode
I
Nail Shear
Nail Shear
Nail Shear
Nail Shear
Nail Shear
Naii Shear
Bearing
Bearing
Beuring
Net Sectior PractuIe
Net Scctiar Pmc ture
Net Sectior Fracturie
Notes: 1: Predicted Shear load b a s 4 on V,=17*n, whcre 17 i s the single shear sbength of a nail obtainrrl from s h w tests, in kN and n is the total nuniber of nails = n,*r 2: Predicted Bearing load based on Bu=3*d*i*n*F,, adapkd fmrn CANJCSA-S16.1-94 (CSA 1994) and wherc n=n,*r
3: Predicteû Net Section Fracture lnd given by Tu=&*Fu, adopted Cmrn CANfCSA-S16.1-94 (CSA 1994), where A, i s ihc gross ara minus
the produci of (nurnber of nails per mw)*(dismeter of nail)*(thickness of critical plaie)
Table 4.3: Staiic Test Results of Plate Specimens
Advanccmcnts in NaiIcd Connections 0bse~cu1~0n.s and Resulrs
Plate 2 (Criticril
Plate)
Test 1.D.
L -
PFN2
PFN2-S
PFN3
PFN3-S
Fatiguc Test Parameters Normolized Data
# of Nails Fr
Row n,
5
Nonnalized Stress ~ a n ~ e '
Number of Cycles to Failurt
N
# of Rows
r
- - 2
Frequenc y
1-k
Failurc Mode
MPa
GrossINet Section Fracture
Net Section Fracture
GrosdNet Section Fracture
Net Section Fracture
Noie: "Naminal Dimensions
I : Normalizcd Areü = I*W-l*n,*d, where i und w iire diniensions of the cniical plate and d is Ow diameier of ihe nail (4.5mm) 2: Nonniilizcd Suess Areu = APIA-,
Table 4.5: Fatigue Test Results of Plate Specimens
Advanccments in Nailcd Connections Observarions and Resuits
Advancemena in Nailed Connections Observations and Resuh
Advancerncnts in Nailed Connections Observations and Resulrr
Advancements in Nileci Connections Observarions and Resulrs
Figure 4.4: Static Base Metal Bearing Failure Mode (Tube Specimen)
Advmccmuits in Ndcd Connections
Advmcerncnts in Nailed Connections Observarions and Resulrr
Advancerncnts in Nailed Connections Observations and Results
Adviuicemenn in NIUled Connections Obseniarions and Resulrs
Figure 4.8: S tatic NaiI S hear Failure Mode (Plate Specimen)
Adviincernents in Nailed Connections Observarions and Resulrs
Admemtnts in Nailcd Connections O&e~anons and Resuiu
Figure 4.1 O: Sratic Base Metal Bearing Failure Mode (Plate Specimen)
Advancemcnts in Nailcd Connections Observations and Re&
Advancemots in Nailai Connections 0&sewmtmtons ond Re&
Figure 4.12: Static Base Metal Net Section Fracnire Failure Mode (Plate Specimen)
67
Advancerncnts in Nailcd Connections Observutions anà Remlu
Advancements in Nailcd Connections Observarions and Restilrs
Figure 4-14 VariabIe Gap Between Tubes Due to Nailing Process
Advanctments in NaiItd Conntcnons Observarions and Resulw
Advanc:rncnts in Nailed Connections Obsrtvarions and Resulrs
Figure 4-16: Nail Shear Fatigue Failure (Tube Specimens)
Advmcements in Nailed Connections Obseservc~rions und Resitlrs
Advancemenrs in NrùIed Connections Observations and Resulrs
Advancementi; in NItiled Connections Observations and Resrrlts
Figure 4.19: Gross/?kt Section Fatigue Failure (Lapped Pht r Specimen: With Bending)
Figure 4.20: Set Section Fatigue FaiIure (Single Plate Specimen: Without Bendingj
74
Advancements in Nailcd Connzcnons Observarions und Resulrs
Figure 3.2 t: Lapped Plate Connection Fatigue Test with Bending (Mazzulla 200 1)
Advanccncnts in Nailcd Connections Obserwriont and Results
Advancerncnts in Nailcd Connections Dùcussion a d Anaiysis of Resulu
5 DISCUSSION AND ANALYSIS OF RESULTS
5.1 STATIC TESTS
5.1.1 GENERAt
A total of nine tube-in-tube connections plus 12 lapped pIate connections were tested
under static loading. Al1 connections failed in the mode predicted, except for three of the lapped
plate connections which were expected to fail by bearing of the cnticai base material, but instead
failed by nail shear failure. For these three tests, the prying due to the eccentricity of the
connection influenced the failure mode. Modifications were made and three additionai plate
bearing tests were performed to ensure bearing failure. The results of al1 static tests are discussed
in this section. The results of tube-in-tube and Iapped plate connections are presented together for
each failure mode.
5.1.2 NAILSHEARFAILLJRE
As documented in Table 5.1, the three tube-in-tube connections which failed in nail shear
reached an ultimate load significantiy higher than the predicted shear capacity (which is based on
the single shear strength of a nail multiplied by the number of nails). However, as Kmtzier
(1994) found, the resistance of the connection is enhanced by the "Nipple-Dimple" effect, fomed
as the nail is driven into the tubes, which creates significant friction between the inner wall of the
outer tube and outer wall of the inner tube. The average shear strength of the nails that Krutzler
(1994) used was 21.15kN and an additional 8.48W on average accounted for the Nipple DimpIe
effect, giving a ratio of 29.63121.15 = 1.40. Similarly, for the tube-in-tube connection tests
conducted in this study, the ratio of actual strength to predicted strength ranges from 1.29 to 1.37.
Figure 4.3 and Table 5.1 show that after the nails failed in shear, the load recovered to
approximately 89% of its ultimate load. The main reason for this behaviour is the fact that the
nail shank failure was not flush with the interfacial surface of the tubes; that is, the sheared nail
promded out of the inner surface of the outer tube and into the outer surface of the inner tube.
As the tubes were pulled apart, the outer surface of the inner tube was being "scratched", or
deformed and yielded by the hctwed nail. (The tube material is softer than the nail material).
As the tubes were pulled apart, material built up around the nail, making it more difficult for the
promding (fractured) nail to pass over, thus causing an increase in load. The maximum mateilal
built up corresponds to the maximum load regained. The load then decreased as the deforrned
(bearing) materiai was pushed aside. This behaviour is favourable but the amount of load
Advancenicnts in Nailcd Connections Discussion and Analysis of ResuIts
regained is unpredictable and unreliable and thus should not be included as an advantage in the
design guldeIines, especiaITy as it Ts ReTy to €x very dependant on the initr'd fit of ùie two tubes.
The behaviour of the six Iapped plate shear tests was slightly different to the tube tests.
Andysis of the static plate shear tests is presented in Table 5.2. Firstly, the maximum shear Ioad
obtained was between 1 .O0 and 1 .O8 times the predicted load, showing that the secondary effect
(Nipple Dirnple) did not develop. (Lower ratios were noticed for PSBLPSB3, where bending
effects due to eccentricity of the plate specimens were pronounced due to the flexible thinner
plate). This is unlike the tube-in-tube connections where the secondary effect significantly
contributed to the strength of the connection. Secondly, once the nails sheared, the plates
completely separated and a regain in load was not possible. The tube connections, on the other
hand, were able to redevelop frictional forces because of the confined tube-in-tube ~ o ~ g u r a t i o n .
Therefore, it may be concluded that when a connection is unconfined, as is the case with lapped
plate connections, secondary effects will not be developed. Fwthermore, for a confined
connection, the amount of additional strength given by frictional forces is not consistent,
therefore unreliable. These are important considerations for developing a general design
recommendation for shear failure of nailed connections.
Overall, the results show that the current recommendation for the static nail shear
strength given by Equation 2.1, which includes a resistance factor of b=0.67 (adopted fmm
CAN/CSA S 16.1-94) would be conservative for both tube spliced connections and lapped plate
connections made with the stainless steel nails. However, more research is required to assess
whether or not Equation 2.1 would apply for nailed connections subjected to a p a t e r amount of
bending.
S. 1.3 BEARING FAILURE
Analyses of the tube and plate bearing tests are provided in Tables 5.3 and 5.4,
respectively. The thne tube bearing tests failed at a load between 1 .O6 and 1.1 1 times the
predicted failure load, which was calcuiated using the same equation for bolted connections as in
the Canadian steel specifcation CANKSA-S16.1-94 (1994), (i.e., Equation 2.2) but excluding
the resistance factor. Similar resuits were found for the second set of bearing plate connections
(PSB 1-A to PSB3-A) where the actual to predicted load ratio was between 1.03 and 1.06. The
original specimens intended for bearing failure (PSB1-PSB3) actually faiIed in shear, as
explained in the section above. even though the predicted bearing failure load was lower than (yet
very close to) the predicted shear failüre load (refer to Table 4.3). Apparently, the bending due to
the eccentricity of the Iapped plates added tension forces to the nails. Therefoce, the combined
Advancementsi in Nailed Connections Discwsion and Analysis of Resulrr
shear and tension forces acting on the nails became more critical than the bearing forces.
Nevertheless, the design Equation (2.2) for the bearing resistance of nailed connections is valid
for bearing-critical tube-in-tube and lapped plate connections made with stainless steel naiIs.
5.1.4 NET SECTION FRAClZTRE
Analysis of the three tube-in-tube net section failures is documented in Table 5.5. The
failure load was between 1.29 and 1.47 times the predicted failure load, which was calculated
using the net area A, [gross cross-sectional area - (number of nails per row)*(diameter of
nail)*(thickness of critical tube)] mdtiplied by the ultimate tensile stress, Fu. Similar results were
found for the lapped plate connections. Analysis of the plate net section fracture tests is
presented in Table 5.6, where the actual to predicted load ratio, based on A a u was between 1.20
and 1.40. The difference in actual to predicted loads can be explained by two main contributing
factors (Lecce 1999). Firstly, the actual net section area is greater than that assumed in the
cdculation. Unlike bolted connections where the tubular materid is drilled or punched out, no
material is eliminated with nailing. Secondly, localised strain hardening surroundhg the nail may
contribute to an increased strength. The sarne conclusions were drawn by Beck and Engeihardt
(2001). as explained in Section 2. Compared to the gross section ultimate strength of the inner
tube (AgFu), the failure load is about 10% to 11% lower for the tube connections (see Table 5.5).
By cornparison, the gross section ultimate strength of the critical plate is between 296 lower and
2% higher than the actual load (see Table 5.6). As a general trend, then, it may be concluded that
the actual effective area contributing to the saength of the connection for this failure mode is
greater than the net area, A, (based on subtracting an area equal to the thickness of the critical
material tirnes the nail diarneter tirnes the number of nails per row from the gross area) but
generally less than the gross area, &. Hence, basing the predicted static ultirnate strength on the
net area, calculated in the manner just described, would give a consemative value for both tube-
in-tube and lapped plate connections.
5.2 FATIGUE TESTS
5.2.1 GENERAL
A total of 16 fatigue tests were conducted including 12 nik-in-tube specimens, 2 single
plate specimens, loaded concenaically, and 2 lapped plate specimens, loaded eccentricdy. As
previously shown in Figure 423, it is evident chat bending gready reduces the fatigue life of a
Advanamcnts in Nailcd Connections Ducussion and Analysis of R u J U
connection and thus must be taken into account. First, analysis of concentrically loaded nailed
connections is carried out, followed by the analysis of eccentrically loaded nailed connections.
5.2.2 CONCENTRICALLY LOADED CONNECTIONS
Analysis was conducted for al1 fatigue failure modes namely shear, bearing and net
section fracture. Two sets of analysis were performed. The fmt involves d l the data obtained for
connections made with the X-CR20 DPlOv fasteners (10 tube-in-tube connections plus 2 single
plate connections). The second involves the data collected for connections made with X-CR20
DP lOv plus that for connections made with ENPH2-2 1L 15 nails (Kosteski et al 2000). This was
done to see if the two sets of fatigue data can be lurnped together to produce one set of design
guidelines or if they should be separated to develop separate design guidelines based on nail type.
The Classification Method was used to analyse the fatigue test results. With this method,
the stress considered is the nominal stress, determined by beam theory. The process to deveIop a
fatigue design ct.uve includes normalitation of the results, linear regression of the data, and
finaily, shifting the S-N curve down by two standard deviations (typical safety caiibration in
North America).
5.2.2-1 Connections with X-CR20 DPl OV Nails
Nonnaiization of Fatirrue Test Results
Normalizing the test results implies a method to find the nominal stress range for each
failure mode. Three faiIure modes were examined, narnely, nail shear failure, base rnetal bearing
failure and base metal net section fracture. The stress ranges were cdculated as the Ioad range,
AP divided by the nominal stress area (Le. the total nail shear area, the total nail bearing area for
the cntical element or the net section area for the critical element). The stress areas have been
cakulated as foiiows:
Nominal Shear Area = n*d2*lr/4
Nominal Bearing Area = dft*n
Nominai Net Area = A, - d*t*n,
where d = nail diameter =45mm,
n = total number of nails,
n, = number of nails per row,
t = thickness of criticd section,
A, = gross area of criticai section
Advancemtnts in Naild Connections Discfcssion and Anafysis of Resuln
Tables 5.7 to 5.9 show the nom-nd areas and stress ranges and Figure 5.1 shows a
graphicd representation of the normalized fatigue results. As detailed in Tables 5.7 to 5.9, the
Iogarithmic values of both the normalized stresses and the actual number of cycles to failure were
calculated. From these values the best-fit line was then determined by linear regression, as shown
in Figure 5.2.
Linear Rearession of Ex~erimentd Data
Linear regression of the experimental data is detailed in Appendix B. The results from
the linear regression are as follows:
Nail Shear Failure (based on shear ma):
Log(Ns) = Log( 1 Z 0 . x 1 0 9 - 8.060Log(SS) ............................... (5.4)
Bearing Failure (based on bearing area):
............................... Log(Nk) = Log( 1 .O 19x 1 02') - 7.9 1 SLog(Sa) (5.51
Net Section Fracture (based on net area):
Log(N3 = ~ o ~ ( 9 . 0 16x 10") - 2.232Log(S,) ............................... (5.6)
The above equations represent a mean best-fit line through the data. These best-fit curves
are shown in Figure 5.3.
Shifting S-N Curve down Two Standard Deviationd Design Cwves
The process to shift the S-N curve d o m by two standard deviauons involves a
cornparison of the predicted fatigue life, given by equations 5.4 to 5.6, to the actual fatigue life,
given by the experimental data. Tables 5.10, 5.1 1 and 5.12, show the process of determinhg the
standard deviation between the actual and predicted fatigue life for nail shear failure, bearing
faiIure and net section fracture, respectively.
Appendix B details the cdculations made to obtain the following design curves:
NaiI Shear FaiIure (based on shear ma):
Log(NJ = ~ o ~ ( 8 . 5 9 6 ~ 109 - 8.060Log(SJ ............................... (5.7)
Bearing Failure (based on bearing area)
............................... Log(&) = ~ o ~ ( 6 . 6 4 8 ~ lon) - 7.9 15Log(Sd (5.8)
Net Section Fracture (based on net a m )
Log(N,) = ~o~(l.923xl0~O) - 223ZLog(S& ............................... (5.9) These design curves are aiso shown in Figure 5.3.
Advancemtnts in Nailed Connections Disct~fsf~on Cyrd A d y s i s of Redts
5.2.22 Connections with X-CR20 DPlûv and ENPH2-2 IL15 Nails
The andysis performed abve for connections made with X-CR20 DPlOv nails was
repeated for connections made with both X-CR20 DPlOv and ENPH2-21L15 nails. (The
ENTH2-21L15 nails were used in tests performed by Kosteski et ai. (2000)).
Normalization of Fatigue Test Results
TabIes 5.13 to 5.15 show the normalized stress ranges and Figure 5.4 shows a graphical
representation of the norrnaiized fatigue results. The data for linear regression is plotted in Figure
5.5. Clearly, it is inappropriate to combine the X-CR20 DPl Ov and ENPH2-2 1L 15 shear data to
fom a best fit line. In fact, the cornputer-generated "best-fit" line (omitted h m Figure 5.5)
produces a positive slope which suggests that fatigue life would increase as stress inmases.
Thus, the evaiuation of combined shear data is abandoned.
Linear Remession of Ex~etirnentai Data
Bearing Failure (based on bearing area):
LOg(Nbr) = ~ o ~ ( 3 . 8 8 2 ~ 1 0 ~ ) - 6.340L0g(Sbr) ......................... ...-(5.10)
Net Section Fracture (based on net area):
Log&) = Log(1.734~ 10") - 2.360Log(S,) ............................. (5.1 1)
The above equations represent a mean kt-f i t line through the data and are shown in Figure
5.6.
Shifting S-N Curve down Two Standard Deviations/ Desim Curves
Tables 5.16 and 5.17, show the process of deterrnining the standard deviation between the
acmd and predicted fatigue life for bearing flilure and net section fracture, respectively
Bearing Failure (based on bearing area)
Log&) = LO~(I .607x 1 0 ~ ) - 6.MOL0g(Sbr) ............................. (5.12)
Net Section Fracture (based on net area)
Log(N,) = ~ o ~ ( 4 . 7 5 0 ~ 10'7 - 2.360Log(Sd ................... ,...,.-( 5.13)
These design curves are shown in Figure 5.6, dong with the best-fit mean h e s determined
above.
Figure 5.7 shows the bearing and net section design curves based on data obtained for X-
CR20 DPlûv naiIs alone and those determined for X-CR20 DPlOv and ENPH2-2lLlS nails
combined, Evidently the differences between the two sets of curves are marginal for bearing and
net section fracture modes, thus a recommendation cm k made based on the combined data. For
Advancemenu in Naïied Coancctions Discussion d Analysis of P e d u
nail shear failure, combining the two sets of data would be unconservative, as aforementioned.
Since nail shear failure is dependent on the nail properties, separate design Cumes should be
developed for each fastener type.
5.2.2 ECCENTRICALLY LOADED CONNECTIONS
Two specimens, namely PSN2 and PSN3. were subjected to eccentric loading. In
recognition of the fact that there is limited data on eccentrïcally loaded nailed connections, the
foliowing analysis is an acadernic exercise and is not meant to develop design recommendations.
The forces of an eccentrically loaded connection includes axial load and bending and the
sum of the two, in terms of stress is as follows:
P/A + M / S
where M=P*e. and ~=w*t2/6
The eccentricity, e, is equal to half of the critical plate thickness (1.49mm). Figure 5.8
illustrates the eccentricity of the lapped plate connections. Table 5.18 shows the axial Ioad, area,
eccennicity, moment and section modulus of the two specimens. The normalized extreme fibre
tensile stress range for the eccentrically loaded specimens PSN2 and PSN3 is based on Equation
5.14. By cornparison, the stress range of the lapped plate connections is about three cimes that of
the single plate connections. These adjusted stress ranges are plotted on Figure 5.9. Cleariy, the
adjusted stress ranges for specimens PSN2 and PSN3 do not foiiow the same trend as the data
points of concentrically loaded specimens PSN2-S and PSN3-S. Adjusting the stress range by
using Equation 5.14 seems to over estimate the stress, and therefore produce consemative results.
However, until more data can be collected, a final recommendation for eccentrically loaded
nailed connections based on the analysis presented here is not appropriate.
Outcr Tube O.D. * t,-,
m m * m 73,0*6.35 73.0*6.35 73.0*6.35
lnner Tube O.D. * ti
Ultimate Load
kN 186 140 153
Maximum h!dict=d
: Minimum 9b of % of
Shear Predicted
Load Ultimate Load ~l t imate Load
Regai ned ( p s t peak) Load Load
( p s t p e w
Standard Deviation COV 0,036 1
Table 5.1: Analysis of Static Nail Shear Test Rcsults (Tube Specimens)
Test I,D.
PSSl PSS2 PSS3 PSB 1 PSB2 PSB3
-- - - --
Plate 1 Plate 2 t 1 *WI t 2 * ~ 2
1 M G Ï ~ Standard Dcviation 0.03 1
COV 0.030
# of Nails n
2 3 4 2 3 4
'l'qble 5.2: Analysis of Suitic Noil Shear Test Results (Plate Specimens)
Ultimart: Lmd
kN 36 55 70 34 51 69
Predicted Shear Load
kN 34 51 68 34 51 68
Actual: Predicted
kN 1 ,O4 1 .O8 1 .O2 1.00 1 .O0 1 .O1
Advanctmtnts in Naiicd Connections Discussion and Alutlys& of Resulu
Tube Fu of inner # of 1 IgD' 1 thklaiess 1 tube 1 Nails
Predicted Acmal Ratio of Failure Faiiure Actual to Load Load Predicted
l kN 1 Load
kN
StandardDeviacion 0.026 COV 0.024
Table 5.3: Analysis of Satic Bearing Test Results (Tube Specimens)
-
Thickness of of # of
Test I.D. Cri tic al Criacal Nails
Plate Plate
Predic ted Ac tuai Failure Failure Load Load
Ratio of Accual to Redicred
Standard Deviation COV 0.019 1
Table 5.4: Analysis of Static Bearing Test Results (Plate Specimens)
-
Test I,D.
- - SN1 SN2 SN3 -
lnner Tube Outer
Diameter O.D.
mm - 60.3 60.3 60.3
Inncr Tuba
Thickncs C i
mm
lnner # of Predicted Predicred lnner Tube Nails # of Failurc Actual Ratio of Failure Ratio of Tube Gross per Rows Load Failure Actual to Load Actual ta
FU Areo Row r bascd on Load Predictcd Bascd on Predicted A, 4 Am' ~ o a d A: ~ ~ i i d
MPa mm2 kN kN 394 518 12 2 143 184 1.29 204 0.90
Mean 1.38 0.89 Standard Deviation 0.095 0.007
m
1 COV 0.069 1 1 0.008
Noies: I : Prdicied Net Swiion Failure load &en by Tu=Aw*Fu, adopted from CAWSA-Sl6.1-94 (CSA 1994), where A, is rhe gross m a minus ihe produci of (number of nails per row)*(diameier of nail)*(îhickness of critical elemcnt) 2: Prdicted Gross Scciion Failure load given by Tu=Ag*Fu
Table 5.5; Analysis of Stütic Net Section Fracture Results (Tube Specirnens)
est I D *
- # of Nails Fr Row
n,
- 4 5 6 -
PSNl
Predictetl Ratio of Failurc Ratio of Actual to h a d Acnial t( Predicted Based on Predictcc;
~ o a d ' A: h d 2
Critical Cntical 'late
Thicknes W idth
t 1 W
nun 98
Notes: 1: Predicled Net Sec(ian Fnilurç load given by Tu=Am*Fu, adopied from CANICSA-S16.1-94 (CSA 1994), where A,, is the gross areu minus ihe produci of (number of nuils per mw)*(Jiameter of nail)*(rhickncss of criiicul element) 2: Predickd Gross Section Failurc load given by Tv=Ag*Fu
Critice I piale
Fu
Mean 1.30 Stanbrd Deviation 0.100
COV 0.077
Table 5.6: Analysis of Static Net Section Fracture Results (Plate Specimens)
Gross of
critical Plate
AI
mm 2.97
1 .O0 0.0 17 0.017
MPa 403
2
291
Test I.D.
K-CR20 DPlOv X-CR20 DPl OW X-CR20 DPlOv
Load Range
AP
kN
160 105 115
Nominal Shcar Arca
As
mm2 127
95 1 1 1
Stress Range
Bascd on Shcar Area
s s
MPa - 1258 1 1 0 0 1033
Number of Cycles to
S hcar Failure Ns
Table 5.7: Rcpmtion of Nomalized Data to be Plorted for Tube Connections failing by ihc Niiil Shear Failure Mode (XCR nails)
Test I.D.
X-CR20 DP~OI X-CR20 DPlOc X-CR20 DPl 01 X-CR20 DPIO\ X-CR20 DPIO\
Load Range
AP kN
Nominal Bearing
Area
Ab
mm2 52 65 77 52 52
S m s Range
Based on Benring
Area
Sb
MPa
581 774 968 87 1 678
Nurnber of Cycles to Bearing Failurc
Nb - 1,126,920 l23,ïOo 19,580 68,080 52 1 .O70
Table 5.8: Praparation of Nomalized Data to be Plotted for Tube Conncciions failing by the Tube Bearing Failure Made (XCR nails)
Test I.D.
FN1 FN2 FN3 FN4
PFN2-S PFN3-S
1 Lord
I Range Fgstener 1.D
K-CR20 DPl OV 85 K-CR20 DPlOv 120 K-CR20 DPlOv 85 X-CR20 DPI OV 55 K-CR20 DPlOv 70
Nominal Net Arca
An,
mm2 363 337 31 1 850 219 21 1
Stress Range
Based on Net Areü
Sn0
MPa
Numbcr of Cycles to
Net Section Faiiure
N",
634,880 284,300 61,260
2,53 1,340 1,501,460 3 16,730
Table 5.9: Prepmtion of Normalized Data to be Ploned for Tube and Plate Connections biling by the Net Section Fracture Friilure Mode (XCR nails)
N,=C/Sm, where C=1.250E+30 and m=8.060
Test No, Festcncr I.D. Stress Actual # of Predictcd #
Range Cycles of Cycles kgNa LogNp
Standard Deviation = 0.08 1 3 2 Standard Deviations = O- 1627
Table 5.10: Siandord Deviation of S-N Experimcntal Results for Tube Connections failing by the Nail
Shem Failure Mode (XCR nails)
Test No.
N,,=C/S'", whcre C=1.019E+28 and m=7.915
Fastcner I.D.
x-CR~O DPl OV X-CR20 DPlOv X-CR20 DPlOv X-CR20 DPl OV X-ÇR20 DPIOV -
S t a n d d Deviation = 0.0926 2 Standard Deviations = 0.1853
Stress Range
Table 5.1 1: Standard Deviation of S-N Experimentll Results for Tube Connections failing by the Tube Beüring Failure Mode (XCR nails)
Accual# of Cycles
Predictcd # of Cycles mPJ,
Np=C/Sm, where C=g.O l6E+ I O and m=2.232
Test No.
FN I FN2 FN3 FN4
PFN2-S PFN3-S
m
~ & n = 0.000 - Smndard Dcviation = 0.3355
' *D*
2 Standard Deviatiorrs = 0.67 1 O J
Table 5.12: Standard Deviation of S-N Experimental Results for Tube and Plntc Connections failing by the Net Section Fracture Failurc Modc (XCR nails)
Smss Rangc
Actual # of Cycles
Predictcd # of Cycles bgN. h$Jp LogNa - Log Np
Stress Range B ascd on S hear
Area
Nurnber of Cycles ta S hcar
Failure
MPa Ss 1 Ns 1
Table 5.13: Prcpiuation of Normalizcd Data to bc Ploned for Tube Connections failing by the Nail Shear Failure Mode (XCR and ENPH nails)
Fastener I.D. Stress Rangc
Based on Bearing Area
Sk MPa
581 774 968 865 678 945 567 1228 756 1071 882 693 504 1131 1006 754
Number of Cyclcs to Bcaring Failurc
Nk
1,126,920 l23,ïOO 19,580 68,080 52 1,070 67,740
1,948,020 10,180
267,740 18,840 63,850 365,600
1,657,090 21,210 56,000 60 1,730
Table 5.14: Preparation of Normalized Data to bc Plotkd for Tube Conncctions failing by the Tube Bearing Failurc Mode (XCR and ENPH nails)
Stress Range Bas& on Nct
Arcri
Sn=
MPa
Number of Cycles to
Net Scction Fûilurc N",
Table 5.1 5: Preparation of Nomdized Data to be Plotted for Tube and Plate Connections failing by the Net Section Fracture Failure Mode (XCR and ENPH mils)
Test No,
FB 1 FI32 Fi33 FEI4 FB5
Fastcner I.D. Smss Range
S 581 774 968 865 678
Actual # of Cyclcs
Na 1,126,920 l23,7ûû 19,580 68,080 52 1,070 67,740
1,948,020 10,180
267,740 18,840 63,850 365,600
1,657,090 21,210 56,000 601.730
Predicted # of Cycles
Np 1,161,174 187,396 45,534 92,578 436.960
Standard Deviation = 0.1914 2 Standard Dcviations = 0.3829
Table 5.1 6: Standard Deviotion of S-N Experimcncal Results for Tube Connections feiling by the Tube Bcaring Failure Mode (XCR und ENPH nails)
Test No,
N,=C/S'", whcre C=lV734E+l 1 and m=2.360
Stress Ronge
Predicted # of Cycles
N, 834,755 372,327 136,699
3,299,011 376,384 394.44 1
Mean = 0,000 rviation = 0.28 12 riations = 0.5623
LogNp
Table 5.17: Sinndard D~viaiion of S-N Experimeninl Results for Tube and Plate Connections failing by the Net Section Fracture Failure Made (XCR and ENPH nuiIs)
LogN, - Log NP
Advanccments in Nailcd Connections Discussion cuzd Anaiysis of Results
hdviincernents in Nailed Connections Discussion arui Andysis of Remlrs
Advancements in Nailed Connections Discussion and Analysis of Results
Advmcements in Nailed Connections Discussion and Analysti of Resulrs
C g a ; z 3 E T . ?
Advnnctmcnts in Nailcd Connections Discussion and Analysis of Resulrs
Advancemencs in Nriild Connections Discussion and Analysis of Results
Advanctments in Nailcd Connections Discussion and Analysis O/ Resulrs
hdvmcementç in EiaiIed Connections Discussion and .4nalysis of Resuln
Mvancomcnts in Naiied Coanectioas Discussion d AnaLyslr of Remlts
Notes:
ti = non-critical plate thickness = 6.07mm tt = criticai plate thickness = 2.971nm et = eccentricity of nonuitical plate = tin = 3.û4mm e~ = eeeentFicity of critical plate = tJ2 = 1.49rnm
Figure is not to scaie
Figure 5.8: Detennining Ecceotricity for Lapped Plate Conneetion
1 o6 Number of Cycles, N
Figure 5.9: Adjusted Stress Rûngcs for Lnpped Plaie Connections
Advanccmtnts in Nailcd Connections Conclusions and Recommendcuwns
6 CONCLUSIONS AM) RECOMMENDATIONS
6.1 CONNECTION STATIC RESISTANCE
6.1.1 GENERAL
The results of nine tube-in-tube plus 12 lapped plate connections have shown that the
static strength design recommendations developed for conventionai nails are vaiid for the new
generation stainless steel nails. The results of the lapped plate connection tests showed that
prying does have an effect on the connection strength, but not signifiant enough to warrant the
development of separate equations. Nevenheless, more research is required to asstss whether or
not the recommendations provided here are applicable for naiied connections subjected to a
greater amount of bending.
6.1.2 NAIL SHEAR RESISTANCE
The shear resistance may be calculated conservatively using the following equation (as
presented in Section 2), (Packer and Henderson 1997):
V, = &*(Shear Strength of ail)' .............. ..+... .... ....... (6.1)
where 'single shear smngth of the nail is determined by labotatory tests
and, $, = 0.67 (adopted from CAN/CSA-S 16.1-94, CSA 1994)
The potential variation between the strengths of different lots of nails is reason enough to
conduct independent shear strengths. However, as other failure modes such as bearing failure are
likely to govern for any practical nailed connection. independent shear tests may not be required,
provided the manufacturer producs the nails to a minimum, guaranteed sûength.
6.1.3 BEARING RESISTANCE
For most practical nailed connections, bearing strength would likely govem and the
resistance cm be calculated using the following equation (as presented in Section 2) (Packer and
Henderson 1997):
Br = 3*h*n*t*d*Fu (adopted h m CANKSAS 16-1-94, CSA 1994) ............. (6.2)
where = 0.67,
and e 23*d
Advanccmcnts in Nailai Connections Conclusions and Recomrnendrrtiom
This design equation, currendy used to determine the bearing resistance of bolted
connections, can be used for nailed connections without being over conservative,
6.1.4 NET SECïION RESISTANCE
The net section resistance cdculation provided in current code specifications for bolted
connections cm be used conservatively for nailed connections. As such, the following
recommendation is made for the net section resistance of a nailed connection:
T, = O.BS*o*A,*F, (adopted from CANKSA-S 16.1-94, CSA 1994) .......... ,. (6.3)
whete, @ = 0.9,
A, = A, - nC*d0*t, ...................... , ........ (6.4)
and d' = 1 .O*(fastener shank diameter)
By cornparison, the cecornmendation made by Beck and Engelhardt (2001) where d8=l. 1 *d would
unjustifiably decrease the net area and provide a net section resistance that is unnecessady over
conservative.
Note that in practice it is unlikely that the spacing of the nails would be so small chat
section fracture would be critical. Instead, bearing failure would be the governing failure mode
for typical naiied connections under static Ioading.
6.2 CONNECTION FATIGUE RESISTANCE
6.2.1 GENERAt
A totd of 12 tube-in-tube plus EWO la@ plate and nvo single plate connedom have
been tested under fatigue loading. The former two lapped plate connections experienced
significant bending under fatigue loading due to the inherent eccentricity of the connection's
lapped confguration. Therefore, the latter two single plate tests were perfomed to examine the
effect of bending on the fatigue iife of the connection. The results show that bending
significandy lowers the fatigue üfe of a connection. The retornmendations provided below are
for concentrically loaded nailed connections. More research is required on eccenaically loaded
nailed connections.
6.2.2 NAIL SHEAR FATIGUE RESISTANCE
The shear fatigue resistance of the X-CR20 DPlOv nails is significantly Iower than that of
the ENPH2-21L15 nails and therefore cannot be "lwnped together" for design purposes.
Nevertheless, the bearing Mure or net section failure (in cases where the nails are closely
spaced) will always be more critical than shear failure. This is evident in Figure 6.1 which shows
that the naiI bearing stress lies above the bearing fatigue curve. Thus, a separate design equation
has not been developed.
6.2.3 BEARING FATIGUE RESISTANCE
The results have shown Little difference between the stainless steel X-CR20-DP10v nails
and the non-stainless steel ENPH2-21L15 nails in a bearing-critical fatigue connection.
Furthemore, bearing failure is a phenornenon of the critical connected element rather than the
connector itself. Furthemore, as shown through the anaiysis, there is little difference between
the design S-N curve developed for connections made with X-CR20 DPlOv nails and that for X-
CR20 DPlOv plus W H 2 - 2 1 L 15 connections, concluding that a separate design equation is not
necessary. Thecefore the following design equation is recommended:
The dope of this equation (m=5) conforms CO current codes found in North America and Europe
for bolted, nveted and welded connections, wherein m=3 or m=5 is typically used. A dope of
m=S was chosen here because it is closest to the "real" denved dope of m=6.34. The above
design recommendation is shown on Figure 6.1 dong with the bearing S-N design curve
developed by Kosteski et al. (2000).
6.2.3 NET SECTION FATIGUE RESIST.WCE
Like bearing failure, net section fracture involves the failure of the critical connected
eIement rather than the connector. Furthemore, the design cuve developed for XCR20 DPIOv
nails is only marginally different to that developed for X-0 DPlOv and ENPH2-22L15 nails
combined. Thus, based on the combined data, the following design equation has been developed
for net section fatigue strength of nailed connections:
Advanccmcnts in Nailcd Connections Conclusions and Recommendations
The conventional value of the slope, m=3 was chosen because it is closest to the "reaP denved
slope of m=2.36, As shown in Figure 6.1, Niessner and Seeger's design curve (1999) is sIightly
unconservahve compared to the design curve developed hem. Nevertheless, current design
standards such as AREA Category D (AREA 1996) for riveted connections may safely be applied
to naiied connections without king over conservathe.
A Betuii~g Data Poiiiis (ENPH2-2 1 L 15) Net Section Fracture Diils Points (X-CIUO DPIOv)
Cl Net Scctio~i Fracturc Data Pokm (ENPH2.2 IL 15) Nail Slieer Data Poiiirs (X-Cm0 DPIOv)
0 Nail Sheiii Data Poiiits (ENPH2-2 1 LI 5) L-UL-L ' 1
1 0" Num ber of Cycles, N
Figure 6.1 : Recommendations for Fatigue Design
Advancemcnts in Naiiled Connections R~erences
Agerskov, H., Fatigue in Steel Structures Unàer Random Loaàing, J o m a l of Constructional Steel Research, Vol. 53, Issue 3, pp. 283-305,2000.
Amencan Association of State Highway and Transportation Oficials, Bridge Design Specflcatiom, SI units. 1' ed., Washington, D.C.. U.S.A.. 1994.
American Railway Engineering Association, Manuul for Railway Engineehg, Steel Structures, Washington D.C., U.S A., Ch. 15, 1996.
Amencan Society for Testing and Materials, Test Methods and Definitions for Mechanical Testing of Steel Products, ASTM A370-97a. West Conshohocken, Pennsylvania, U.S.A., 1997.
American Society for Testing and Materials, Specification for Cold- Fonned Welded and Seamless Carbon Steel Structural Tesring in Roundr and Shapes, ASTM A500-99, West Conshohocken, Pennsylvania, U.S.A., 1997.
American Society for Testing and Materials, S p e c i m o n for Steel, Sheet and Strip, Hot Rolled, Carbon. Structurd, High Strength Low Alloy und High Strength Low Alloy with Impmved Fonnobiliry, ASTM A IO 1 1/A 10 1 1M-00 West Conshohocken, Pennsylvania, U.S.A., 2000.
American Welding Society, Structural Welding Code - Steel. 1 7 ~ ed., AWS D 1.1:2000, American Welding Society, Miami, Florida, U.S.A., pp. 24 -29,2000.
Beck, H., Influence of DX-farteners. Drilled Holes, Se[fdrilling Screws and Pu& Welds on the Static Stress-Strain Behaviour of Strucntrd Steel, Arnerican Institute of S tee1 Construction Research Project: Applicaaons in Steel Consüuction, Hilti Corporate Research, Hilti AG, Schaan, Liechtenstein, 1997.
Becic, H., Nailed Shear Conneetion In Composite Tube Colurnns, 2* European Conference on Steel S tnictures, Prague, Czech Repub tic, pp. 35-53, 1999a.
Beck, H., DX-Stahlan wendungen Obere Anwendungsgrenze fùr Verzinkte Rostfreie Nagel, Report XE-99-20, Hilti AG, Schaan, Liechtenstein, 1999b.
Beck, H., Yokohama Pier Project - DyMmic and Static Sheur Tests with X-CR20 DPIO, Hilti Report XE-00-48, Hilti AG, Schaan, Liechtenstein, 18 pp., 2000.
Beck H. and Engel hardt, M ., D., Net Section Eficiency of Steel Coupons with Po wder Actuated Fasteners, Hilti AG Report, Schaan, Liechtenstein, 200 1.
Canadian Institute of Steel Construction Handbook of Steel Construction 7' ed., Willowdaie, Ontario, Canada, 2000.
Canadian Standards Association, Limit States Design of Steel Structures, CANKS A-S 16.1-94, Rexdale, Ontario, Canada, 1994.
Canadian Standards Association, General Requiremm for Rulled o r Welded Structural Qualiity SteeUStructurd Quaiity Steel, G40.2OIG40.21-98, Etobicoke, Ontario, Canada, 1998.
Eqgeba4 M, D, Kates Z, Re& I L and Stasney, B., Ejsperimem un the Eflecu of Power A c w e d Fasteners on the Strength of Open Web Steel Joists, Engineering Journal, Amencan Institute of Steel Construction, Fourth Quarter, Vol. 37, No. 4, pp. 157-167, 2000.
European Cornmittee for Standardization, Eurocode 3: Design of Steel Structures. ENV 1993-1 -1, Bmssels, Belgium, 1992.
Gaiambos, T.V. (ed.), Guide tu Stability Design Criteria for Metal Structures, 5fi cd., Wiley & Sons, New York, U.S.A., pp. 8 14-822, 1998. (Technical Memorandum No. 3 of the Structural Stability Research Council: S tub-Column Test Procedure).
Hilti Fastening Technology Manual, Secaon C3, Issue 1 O/96, Hilti Corp., Schaan. Liechtenstein, pp. 14-15, 1996.
Hilti AG, Corrosion Resistonce of the X-CR mil: Cornparison with AlSI 301 and AISI 3I6, Otto- Graf-Institut Report, Universitat Stuttgart, Forschungs-und Materialpüfungsanstait Fur das Bauwesen, Germany, 2000.
Huber, G., Millennim Tower in Vienna: Semi-continuous Connections between Composite Slim Fluors ami Composite Tubular Columnr. gh International Symposium uid Euroconference on Tubular Structures, Düsseldorf, Germany, pp. 57-64,2001.
Kosteski, N., Nailed Tubular Connections, Master of Applied Science Thesis, University of Toronto, Toronto, Ontario, Canada, 1996.
Kosteski, N,, Packer, LA., and Lecce, M., Nailed Tubular Connections Uncier Fatigue Luaàing, Journal of Structurai Engineering, American Society of Civil Engineers, Vol. 126, NO. 1 1, pp. 1258-1267,2000.
Krutzler, R.T., Nailed Tubular Connections M e r Axial Loading, Master of Applied Science Thesis, University of Toronto, Toronto, Ontario, Canada, 1994.
Kulak, G. L,, Fatigue Strength of Rivered Shear Splices, Progress in Structural Engineering and Materials, Vol. 2, Issue 1, pp. 110-1 19, 2000.
KuIak, G. L., and Gîtmor, M. t, Limit States Design in Stmcturut Sreet, 6" ed., Canadian Institute of Steel Construction, Willowdale, Ontario, Canada, 1998.
Lecce, M., Section Fracture in Nailed Tubular Connections, Bachelor of Ap piied Science Thesis, University of Toronto, Toronto, Ontario, Canada, 1999.
Mazzulia, M., Nailed Plate Connections, Bachelor of Applied Science Thesis, University of Toronto, Toronto, Ontario, Canada, 200 1.
Niessner, M., and Seeger, T. Fatigue Strength of Structural Steel with Pawder Actuated Fasteners According ro Eurocode 3, Stahlbau, Vol. 68, Issue 1 1, pp- 94 1-948, 1999.
Advanccments in Naiiled Connections References
Packer, J.A., and Henderson, LE., Hollow Structural Section Connections and Twses: A DPsigrr Gni& e&, CanadiairImtimtcof Steek e-, WitlowMe, Ontno. Canada, pp. 267-270, 1997.
Xie, M., Besant, G., T., Chapman, J., C., and Hobbs, R., E., Fatigue of Riveted Bridge Girders, The Structural Engineer, Institution of Structural Engineers, Vol. 79, No. 9, pp. 27-36.20 1.
APPENDIX A - Material Test Data
l ---- Coupon la I - Coupon lb 1
Figure A. 1 : Tube 1 Coupon Test Resuits (60.3~3.18 mm circular HSS)
Advanctmtnts in Naiied Connections Appendir A
I ---- Coupon 2a 1 - Coupon 2b
Figure A.2: Tube 2 Coupon Test Results (60.3~3.18 mm cimlar HSS)
Advanctmtnts in Nailed Connections Appendk A
- . - O Coupon 3a 1 - Coupon 3b
I ---- Coupon 3a I - coupon 3b 1
Figure A.3: Tube 3 Coupon Test Results (60.3x6.34 mm circular HSS)
Advanccments in Nailed Connections AppendUr A
---. Coupon 4a 1 - Coupon 4b
---. Coupon 4a
- Coupon 4b ]
Figure A.4: Tube 4 Coupon Test Resuits (60.3x6.35 mm circular HSS)
Advancemcnts in Nailai Connections Appendu A
/ c i 1 Coupon 5b
Coupun Sa 1 - Coupon 5b
Figure AS: Tube 5 Coupon Test Results (73.0x6.35mm circular HSS)
Advanccrncnts in NaiIed Connections Appendù A
o.-- Coupon 6a I - Coupon 6b
Coupon 6a
Figure A.6: Tube 6 Coupon Tac Resuits (73.0x6.35mm circular HSS)
Advanccmcnts in Nailed Connections AppendUF A
---- Coupon 7a 1 - Coupon 7b
---- Coupon 7a 1 - Coupon 7b
Figure A.7: Tube 7 Coupon Test Renilts (73.0x6.35rnm circular HSS)
122
Advanctmcnts in Nailed Connections Appenàu A
Figure A.8: Stub Column Test Results for Tube 1 (HSS 60.3x3.18mm)
Advancemcnts in Nailai Connections Appmdk A
O 0.002 0.004 0.006 0.008 0.01
Strain (E)
Figure A.9: Saib Column Test Resula for Tube 4 (HSS 60.3x6.35mm)
Advanccmcnts in Nailed Connections Appendix A
I
I-Tube61 i
i
I I I
O 0.02 0.04 0.06 0.08 O. 1
Strain (E)
0 0.002 0.004 0.006 0.008 0.01
Strain (6)
Figure A. IO: Stub Column Test Results for Tube 6 (HSS 73 .Ox6.3Smm)
Advanccments in NaiIcd Connections ADD& B
APPENDIX B - Analvsis of Fatimre ResuIts - Calculations
DETERMI[NING S-N DESIGN CURVES (Kosteski 1996)
General
The equation of a curve on a log-log S-N graph is given by the following:
LogN = Loge -m*LogS .....................O..... ... (B.1)
where N = number of cycles,
C = intercept vaiue
S = stress range
m = slope of the line
Figure 5.2 gives the equations which describe the best-fit lines of the expenmental data in the
form of LogN. = LogC - m*LogS, where LogN. and LogS are known values. Hence. the
intercept, C, can be calculated. Once C and m are calculated, the "mean S-N" curve cm be
established. The next step is to shift the mean S-N cuve down by two standard deviations to
obtain the equation of the design curve, parailel to the best-fit line. This is accomplished by
obtaining a new intercept value (C,) and C, = &&O- where 2stddev = 2*standard
deviation given in Tables 5.10 to 5.12. This process is shown for d l failure modes.
Nailed Connection Example: Bearinp Failure Mode - XCR nails)
Detennining Mean Line
Lo@, = -791SLogS + 28.008 ( h m Fig. 5.2)
LogC = 28.008
C = 1 0 ~ - ~ ' = 1.019~1028
.: LogN = Log( 1 .O l9x 1 0 ~ ) - 7 9 15LogS
Advanccments in Nailcd Connections Appendù B
Detennining the Design Curve
2"Standard Deviation = 0.185 (frorn Table 5.1 1)