timber rivet connections

Timber Rivet Connections The Design Process Revealed Robert J. Taylor, PhD, P.Eng., Assoc.AIA* David M. Moses, PhD, P.Eng., PE, LEEDAP** * Director, Technology Transfer, American Forest & Paper Association / American Wood Council, Washington, DC ** Structural Engineer, Equilibrium Consulting Inc, Vancouver and Toronto, Canada

INTRODUCTION Timber rivet connections have been used successfully in many structures over the past 30 years. They are part of the US1 and Canadian2 structural wood design codes, but unfortunately, there are few published design examples to aid designers3,4,5,6. This paper is targeted to the connection designer and provides a short summary of the 2005 NDS design process for timber rivet connections along with comments on design issues of common interest.

Features and Installation In essence, timber rivet connections can be characterized as large, thick truss plates. The hole diameter and the dimensions of the rivet head are important factors required to develop "head fixity." Some rivets with small heads may not develop this characteristic. The tensile strength of the rivets themselves is also very important and manufacturers of rivets must pay attention to this (not necessarily the connection designers). Dimensional details of the rivet system using specially shaped steel nails installed in a perforated steel plate are described in the 2005 NDS1, Appendix M. Timber rivets have a unique installation procedure that is noted in

CSA O86 and further explained in its Commentary: Timber rivets at the perimeter of the group shall be driven first. Successive timber rivets should be driven in a spiral pattern from the outside to the centre of the group. In Dr. Madsens book Behaviour of Timber Connections7, he describes the original line of reasoning behind this procedure:

"The 'oval' cross section of the rivet with its long dimension placed parallel with the grain (even when the load is perpendicular to the grain) does not cut the fibres, but pushes the fibres to each side as the rivet is driven into place...the fibres between two [adjacent] rivets are compacted initially by about 25%..." i.e. the fibres are compressed by the rivets "creating 'friction' between fibres and the rivets, in addition to the usual nail action." [There is a] very strong interaction between the steel plate and the fibres contained within the perimeter of the rivet group and to a depth equal to the rivet penetration. At the same time, the pre-stressed fibres will not be able to create splitting in the glulam; on the contrary, it prevents splitting from occuring. The rivets create a plug of wood which is reinforced and firmly integrated with the steel plate." Dr. Madsen describes the fixity of the rivet head as a result of deforming the head when the rivets are driven: "...when the conical head is driven into the steel plate [the] hole becomes deformed and...keeps the rivet in that position. The rivet is now acting as a fully fixed cantilever beam reaching into the wood fibres.

Clearly, the state of stress in a rivet connection is quite complex and the design procedures presented in the design codes are meant to simplify the analysis for day-to-day use.

Timber Rivet Connections - The Design Process Revealed 1

Connection Strength The main advantage of using timber rivets lies in their ability to develop very high loads compared to other conventional connectors in timber. As of this writing, the 2005 NDS limits the installation of timber rivets only into Douglas Fir-Larch or Southern Pine glued laminated timber (manufactured in accordance with ANSI/AITC A190.1), whereas CAN/CSA-O86-01 permits rivet installation into other common structural wood products through the use of a listed factor, H (10.7.2.2) applied to the factored lateral strength resistance of a connection loaded either parallel or perpendicular to grain. Test data8,9,10 and rationale used for developing the CSA O86 provisions for timber rivets installed in solid sawn material showed that timber rivet capacity for Douglas Fir-Larch glulam and Douglas Fir-Larch solid sawn lumber were comparable. The test failure modes were rivet yielding, but concern had been expressed that wood checks and splits are more prevalent in solid sawn material than glulam. So, although the test results were comparable, the H factor for solid sawn stated in the code is 50% of the H factor for glulam to allow for checks and splits in solid sawn. Designers often ask: does it matter which wood surface the timber connection is installed in? From the research3,7,8,9,10,11,12, there does not appear to be much difference in lateral load design capacity between face surface installations (surfaces 1 and 2 in Figure 1) in parallel and perpendicular to the grain directions for timber rivet connections. Differences between surface 1 and 2 capacities are small in rivet yielding, but maybe more so for wood failure modes between each surface particularly in the perpendicular to grain direction. For design, these differences are small enough that installations in surfaces 1 and 2 can be treated the same. However, end grain (surface 3) installation design capacity is considerably lowered per NDS 13.2.5 and O86 10.7.2.7, roughly half of the perpendicular-to-grain surface 1 or 2 value for a 90 degree cut. Timber rivet connections, originally developed for use with glulam construction, may be a viable option for use with structural composite lumber (SCL) products. Tests13 have been conducted on small samples to assess the performance and predictability of timber rivet connections in parallel strand lumber (PSL) and laminated strand lumber (LSL). The test joint configurations were designed to exhibit rivet failures in some combination of rivet yield and bearing deformation in the composite as opposed to brittle wood failure modes, such as block-shear tear-out or splitting. Results suggest that per-rivet design values should fall between 225 to 450 lbs (1 and 2 kN), depending on species and density of the composite and load direction with respect to grain of the composite strands. Timber rivets performed better in LSL than in PSL and better in yellow poplar PSL than in Douglas-fir or Southern Pine PSL; 1 inch (40-mm) rivets in yellow poplar LSL gave roughly equivalent performance to 2 inch (65-mm) rivets in yellow poplar PSL. Comparing rivet yield predictions following the National Design Specification recommendations for round nails and the much simpler approach of using 2/3 the maximum load suggests that the latter approach provides a more consistently reliable evaluation of yield strength for timber rivets. Rivets in SCL are not currently addressed by the design codes. Additional study is still necessary to assess rivet connection performance in SCL when rivet density exceeds one rivet per square inch. Moisture Issues Designers are often concerned about cross-grain movement of wood due to moisture changes, especially with respect to timber connections using wide side plates, or where fasteners are designed as large groups on a common plate. There is a belief that timber rivets on wide plates can accommodate wood cross-grain shrinkage / expansion

Douglas Fir-Larch glulam 1.0 Spruce-Lodgepole Pine Jack Pine glulam 0.80 Douglas Fir-Larch sawn timber 0.50 Hem-Fir sawn timber 0.45 Spruce-Pine-Fir sawn timber 0.40 Northern Species sawn timber 0.35

Figure 1 Glulam Surfaces

CAN/CSA-O86-01(10.7.2.2) H Factor


due to MC change without inducing tension perpendicular stresses in the wood fiber around the rivet shanks; however, it is still a matter of the degree of MC change in the wood, and the scale of the rivets, plate(s), and cross-grain dimension of wood member relative to each other. Standard connection practice is to never use a single steel splice plate on connections where the distance between outer rows of dowel connectors is greater than 5" (NDS Figure 11H). CSA O86 Clause 10.7.1.10 states, For wet fabrication conditions in sawn lumber, the maximum dimension perpendicular to grain over which a rivet group spans shall not exceed 200 mm (8 inches). This accounts for shrinkage in the long term to prevent splitting, i.e., the timber shrinks but the steel plate does not, and tension perpendicular to grain develops which may result in splitting. Timber rivets, on the other hand (as opposed to dowel-type connectors), have been tested and modeled for the group sizes indicated in the code tables. These tables in the NDS and O86 limit the size of the rivet groups and were developed using analytical models confirmed with testing for groups within that range (see references). In terms of addressing the shrinkage/splitting concern with the drying of wet lumber, there were tests5 that looked at various environmental conditions. However, glulam is made from kiln-dried material and should be much more stable than solid sawn, non-kiln-dried material. It would, therefore, be prudent, as a connection designer to keep this in mind when designing large groups of rivets, i.e. the material being specified, the anticipated service conditions, and the distance between the outermost rows of rivets on a common plate. Introducing more plates separated across the wood grain could alleviate this concern. In practice, however, the authors have never run into this issue as a problem. Good practice is to always hot-dip galvanize metal components for corrosive or exposed environments and in situations where the structure may be exposed to the elements for long-construction periods that might otherwise result in streaking stains on the wood that can be very difficult to remove (unsightly if the final structure is meant to be exposed for aesthetics). The 2005 NDS specifies timber rivets made of mild steel (AISI 1035), and plates of A36 steel. Further, design provisions and values of the 2005 NDS are applicable only to timber rivets that are hot-dipped galvanized to ASTM A153. Plates also need to be hot-dipped galvanized to ASTM A153 if the connection is in wet service. This is all described in 2005 NDS 13.1.1. Moment Resisting Applications Timber rivet connections work best when the plate of rivets is loaded in one direction as a group. The system was never intended to be used to resist a twisting moment applied in the plane of the plate. Madsen7 contends that a circular arrangement of rivets for such moment connections might make an interesting research problem, however, based on engineering experience, and the likely development of undesirable tension stresses perpendicular-to-grain14, in-plane moment connections using timber rivets would not be recommended. Instead, designers can use other strategies to transfer moment, one of which is exemplified later in this paper. Seismic Connections Regarding seismic performance, obviously ductility can be enforced in the design of rivet connections by designing for rivet failure as the governing mode (i.e. ductile, as opposed to brittle wood failure). Dr. Marjan Popovski at FPInnovations (formerly Forintek Western Laboratory) contends that timber riveted connections are definitely one of the best connections to be used in earthquake prone areas. As proof, he has conducted exhaustive tests, including shake table tests, the results of which have been published15,16. In earthquake prone areas, timber rivet connections should be designed to fail in rivet yielding in order for the structure to achieve the required connection ductility. Wood failure (brittle mode governing) should be avoided at any cost. An improved way to enforce connection ductility is to move the ductile zone out of the rivets into the steel plates. There is far superior confidence in the ability to predict ductile behavior in structural steel, so if the steel plates are designed as the weak link, i.e. the fuse or energy-dissipating element of the connection, one can control and predict the ductility of the connection prior to approaching the capacity of the rivet connection in the wood. Here is an illustrative example: picture a splice between 2 pieces of wood where the steel side plates are riveted to both sides of each piece, but the steel plates are short and not continuous between wood members. Instead, use steel bolts A325 or similar to bolt the steel plates together with steel splice plates - essentially a steel-steel connection. Other configurations are possible too, essentially moving the weak link into the steel plates where one can more accurately predict behavior.


DESIGN PROCESS The design process for timber rivets is illustrated through three worked examples of typical connections using allowable stress design (ASD) and load resistance factor design (LRFD). Essentially, there are four strength limit states to a timber rivet connection; two parallel-to-wood-grain (P-direction), and two perpendicular-to-wood grain (Q-direction). For each grain direction either the rivet yields and fails, or the wood fiber fails. If the load is applied only in the P-direction, or only in the Q-direction, then the number of strength limit states to check reduces to two: rivet yielding, and wood fiber failure. The lower strength will govern the design. The perforated plate is stiff and, although rarely an issue, should

also be checked using appropriate steel code provisions17,18. Although as mentioned previously, this potential limit state in the plates tensile capacity could be added to the above states should one wish to assure connection ductility. The design process is simple, regardless whether ASD or LRFD is used, and is best implemented using a spreadsheet, or other calculation software because of its recursive nature: Determine total loads that must be resisted (demand)

Assume a trial design based on connection configuration geometry that will accommodate a grid of rivets,

minding tabulated minimum edge and end distances. The main variables here are: plate thickness, rivet length, rivet spacing parallel to wood grain, number of rows of rivets, and number of rivets in each row.

Check rivet yield failure an equation is given for this based on the capacity of a single rivet through a

single plate. There are two equations: one each for the P and Q directions respectively (NDS 13.2-1 and 13.2-2).

Check wood failure parallel-to-grain (P-direction) from a table based on rivets installed on faces of the

connection. The tables are organized by rivet length and by plate thickness for typical rivet grid spacings. Footnotes to the table offer explanations of member width. The tables simplify the design process tremendously and allow the designer to avoid using the complex equations for predicting wood failure in shear or tension. The equations were originally developed and verified by tests8. For details on these equations, see the 2005 NDS Commentary.

NDS Tables 13.2.1A 13.2.1F are for connections with steel side plates on opposite sides of the wood member. The reference design value in the table is for the capacity of one side plate with associated rivets (NDS C13.2.1). Thus for a connection with plates on opposing faces, the designer would double the table value to determine the reference capacity of the connection. For connections with a single plate of rivets on one side of the wood member, the designer enters the table with twice the thickness of the wood member to get the correct reference capacity for a single-sided connection.

Check wood failure perpendicular-to-grain (Q-direction) an equation (NDS 13.2-3) is given for this based on the capacity of a single rivet through a single plate. The equation references two tables: one for the reference value (NDS Table 13.2.2A) based on one plate with rivets installed in one side face of the connection, and another for the Geometry Factor, C , (NDS Table 13.2.2B). Again, the reference design value obtained from the equation is doubled for connections having two side plates.

The lowest capacity of four failure checks above will govern the capacity of the connection. If rivet yield

governs, then ductility of the connection is assured. If wood failure controls, the connection is likely to be less ductile.

Adjust the determined capacity for site environmental conditions using adjustment factors.

Calculate the demand:capacity ratio a value less than 1.0 is safe. If the ratio is greater than 1.0, try adding

more rivets and repeat the trial design. Off the table for number of rivets? Try increasing the rivet spacing


parallel-to-grain and move to another table. No good? Try increasing the plate thickness. Still not enough? Try increasing the rivet length in increments to the maximum penetration permitted by the connection geometry, and repeat the trial.

A handy flowchart in Figure 2 is helpful to illustrate the flow of the design process as referenced to the 2005 NDS. In short order, mastery of the process can be obtained.

DESIGN EXAMPLES To illustrate the design process, a series of examples is provided. Each example is worked in both ASD and LRFD and is based on the 2005 NDS timber rivet provisions found in Chapter 13. Each solution has been developed using Mathcad software by Parametric Technology Corporation (PTC). Therefore, formatting of certain variables and equations as shown in the examples are unique to this software.

Example 1 Tension Splice For the first example in Figure 3, consider a simple tension splice loaded in the wood parallel-to-grain direction (P), with rivet plates installed on opposing wood faces. Here, three strength limit states are of interest: rivet strength, parallel-to-grain wood strength, and tensile strength of the perforated connecting plate.

Example 2 Hanger Connection For the second example in Figure 4, consider a beam-to-girder hanger connection, with the hanger installed with rivets to one wood face of the girder and loaded in the girder perpendicular-to-grain direction. Here, two strength limit states are of interest: rivet strength, and perpendicular-to-grain wood strength. The hanger is assumed to be structurally adequate. In the example, three trials are run. The first trial with the wood failure governing does not work, however the second trial where rivet failure governs does work simply by adding more rivets and providing desirable connection ductility in the bargain. The third trial shows a way of preserving the desired rivet yielding mode with fewer rivets, by relocating the rivet array closer to the top face of the girder.

Example 3 Moment Connection For the third example in Figure 5, consider a three-pinned Douglas Fir glulam arch spanning 300 feet. Each half of the arch needs to be spliced at its midpoint for shipping, and the moment splice needs to be designed for wind uplift. Here, axial and shear loads are ignored for illustration of the design process but would be required in reality. The splice connection uses a single rivet plate at the top and bottom of the member and opposing plates on the sides of the member to develop the tension force across the splice due to the moment. This strategy would keep tension-perpendicular stresses to a minimum. The design is done in two steps:

- Step 1: design of the top rivet plate to take most of the moment - Step 2: design of side rivet plates to take the remaining moment

Additional steps to complete the design are not shown here. These steps include design of split rings or shear keys to resist shear, as well as checking of plate thicknesses, net section, and addition of plate stiffeners as required. Checking rivet group block pull-out failure of the wood member, or other known local stress effects due to the

Photo credit: R. Malczyk, Equilibrium Consulting Inc.


rivets, is not needed since these failure modes were included in the generation of the 2005 NDS timber rivet table values see 2005 NDS E.1.1 for information.

SUMMARY Timber rivets are a versatile means of making large scale timber connections functionally and aesthetically possible. The design of timber rivet connections using current code references is presented in a manner that the designer can easily follow. Examples from real life are provided to illustrate the process and to aid the designer in this task.

ACKNOWLEDGEMENT Gratitude is expressed to the many contributors during the discussion and development of this paper, including: Erol Karacabeyli (FPInnovations/Forintek), Marjan Popovski (FPInnovations/Forintek), Bruce Craig (Weyerhaeuser), Doug Rammer (USDA Forest Products Laboratory), Jeff Linville (AITC), Phil Line (AF&PA / AWC), and Robert Malczyk (Equilibrium Consulting Inc.) who provided the basis for the moment connection example (Example 3). The authors wish to acknowledge the work of the inventor of the timber rivet, Dr. Borg Madsen, on whose work many others have since contributed to the design and implementation of the timber rivet connection. Today, the timber rivet is gaining widespread use as an effective and versatile timber connector.

DISCLAIMER It is intended that this paper be used in conjunction with competent engineering design. The authors, AF&PA, and Equilibrium Consulting Inc. assume no responsibility for errors and/or omissions in this paper, nor for any engineering designs, plans, or construction prepared from it.

REFERENCES

1. ANSI / AF&PA NDS-2005, National Design Specification (NDS) for Wood Construction, 2005 Edition, American Forest & Paper Association, Washington, DC.

2. CAN/CSA-O86-01, Engineering Design in Wood (Limit States Design), Canadian Standards

Association, Rexdale (Toronto), ON, Canada.

3. Foschi, R.O.; Longworth, J. (1975): Analysis and Design of Griplam Nailed Connections, Journal of the Structural Engineering Division, American Society of Civil Engineers, 101(ST 12): 2537-2555.

4. Fox, S.P. (1979): Connection Capacity of New Griplam Nails, Canadian Journal of Civil Engineering,

NRCC, 6(1):59-64.

5. Stahl, D.C.; Begel, M.; Wolfe, R.W. (2000): Simplified Analysis of Timber Rivet Connections, Proceedings of World Conference on Timber Engineering 2000, Whistler Resort, BC, Canada, Jul 31 Aug 3, 2000.

6. Williams, C.C. (2006): Timber Rivets, Structure magazine, NCSEA / CASE / SEI, Copper Creek

publishers, Reedsburg, WI, 13(3):26-27.

7. Madsen, B. (2000): Behaviour of Timber Connections, Timber Engineering Ltd., North Vancouver, BC, ISBN 1-55056-738-1. 430 p.

8. Karacabeyli, E., Foschi, R.O. (1987): Glulam rivet connections under eccentric loading, Canadian

Journal of Civil Engineering, NRCC, 14( ):621-630.

9. Karacabeyli, E.; Fraser, H. (1990): Short-term strength of glulam rivet connections made with spruce and Douglas-fir glulam and Douglas-fir solid timber. Canadian. Journal of Civil Engineering, 17(2):166-172.


10. Karacabeyli, E.; Fraser, H.; Deacon, W. (1998): Lateral and Withdrawal Load Resistance of Glulam Rivet Connections Made with Sawn Timber, Canadian Journal of Civil Engineering, (25):128-138.

11. McGowan, W.M. & Madsen, B. (1965): A Rigid Field Joint for Glued-Laminated Construction,

Cooperative Study Report by the Forest Products Laboratory, Vancouver, and Research Committee of the Canadian Institute of Timber Construction, Vancouver: Forest Products Laboratory.

12. Foschi, R.O., Folz, B.R., Yao, F.Z. (1989): Reliability-based Design of Wood Structures, Structural

Research Series, Report No. 34, Department of Civil Engineering, University of British Columbia, 282 p.

13. Wolfe, R. W.; Begel, M.; Craig, B. (2004): Timber Rivets in Structural Composite Lumber, General Technical. Report FPL-GTR-153, U.S. Department of Agriculture, Forest Service, Forest Products Laboratory, Madison, WI, 9 p.

14. Hampson, J.A.; Prion, H.G.L.; Lam, F. (2003) : The Effect of End Distance on the Moment Resistance of

Timber Rivet Connections, Canadian Journal of Civil Engineering, NRCC, (30):945-948.

15. Popovski, M.; Prion, H.G.L.; Karacabeyli, E. (2002): Seismic Performance of Connections in Heavy Timber Construction, Canadian Journal of Civil Engineering, 29(2002): 289-399.

16. Popovski, M.; Karacabeyli, E. (2004): Seismic Performance of Riveted Connections in Heavy Timber

Construction, Paper No. 3356, Proceedings 13th World Conference on Earthquake Engineering, Vancouver, BC, August 1-6, 2004.

17. AISC (1989): ASD Manual of Steel Construction, 9th Edition, American Institute of Steel Construction,

Inc., Chicago, IL.

18. AISC (1998): LRFD Manual of Steel Construction, 2nd Edition, American Institute of Steel Construction, Inc., Chicago, IL.

19. http://www.timsys.com/html/pricing.html Canadian and US primary source of timber rivets.


Determine: Rivet Grain Capacity (13.2-2) Qr = 160 p0.32 nR nC

Determine: Wood Grain Capacity (13.2-3) Qw = qw p0.8 C Table 13.2.2A qw Table 13.2.2B C

Determine: Lowest Governing Capacity in each direction Min (Pw, Qw) and Min (Pr, Qr)

Apply: Strength Adjustment Factors for Site Conditions to Min (Pw, Qw, Pr, Qr) to get P and Q Table 10.3.1 Footnotes 4, 5, 6 (10.3.2); Table 2.3.2; Appendix B CD Table 10.3.3 CM Table 10.3.4 Ct Table 13.2.3 Cst (10.3.7; N.3.1); Table N1 KF (10.3.8; N.3.2); Table N2 z (10.3.9; N.3.3); Table N3 Number of Plates nP

Adjust as needed: Plate Thickness ts Rivet Length (calc penetration 13.2.1) p Rivet Spacing || Grain sp Row Spacing Grain sq Number of Rivets in Each Row nC Number of Rows nR

Determine: Demand / Capacity Ratio N / N

Demand / Capacity 1.0

Stop

N

Y

Load Perpendicular to

Wood Grain Q

Y

N

Start

Determine: Demand Loads; resolve to || and grain directions (13.2-4) N, P, Q

Determine: Minimum Edge / End Distances Table 13.3.2 ap, aq, ep, eq

Choose: Plate Thickness ts Rivet Length (calc penetration 13.2.1) p Rivet Spacing || Grain sp Row Spacing Grain sq Number of Rivets in Each Row nC Number of Rows nR

Load Parallel to Wood Grain

P

Determine: Rivet || Grain Capacity (13.2-1) Pr = 280 p0.32 nR nC

Determine: Wood || Grain Capacity Table 13.2.1A-F Pw

Y

N

Determine: Capacity Loads; resolve from || and grain directions (13.2-4) N, P, Q

Figure 2: Timber Rivet Design Process Flowchart (referenced to 2005 NDS) Timber Rivet Connections - The Design Process Revealed 8

CM 0.8:= Wet service (Table 10.3.3)Ct 1.0:= Less than 100 deg F (Table 10.3.4)Cst 0.90:= 3/16" steel plate (Table 13.2.3)

C = N/A (Table 13.2.2B and Table 10.3.1 Footnote 6)

Demand ASD LRFDD 4400lbf:=S 13200lbf:=

T D S+:= Tf 1.2 D 1.6 S+:=T 17600 lbf= Tf 26400 lbf=

Figure 3Example 1: Timber Rivets - ASD & LRFDDetermine the number of rivets required for the wet service tension splice shown below. The glulam members are 3"x9" Southern Pine. The tensile force is due to dead plus snow load. Use 1-1/2" rivets and 3/16" steel side plates, and the 2005 NDS provisions. Note that the designer must also check member capacity and rivet plate capacity.

Wood: b 3in:= Rivet/Plate: lr 1.5in:=d 9in:= tp 0.1875in:=

hp9in32

:= Hole diameter

np 2:= Number of platesModification factors (Table 10.3.1):

CD 1.15:= Load Duration / Time Effect(ASD - Table 2.3.2, LRFD - Table N3)Snow Load

0.8:=z 0.65:=

KF2.16z

:= KF 3.323=


p 1.187=nR 8=nc 10:=Pr 280 p

0.32 nR nc lbf:= Pr 23666.322 lbf= 2005 NDS (13.2-1)Take the minimum of wood or rivet capacity:

P min Pw Pr,( ):= P 21390 lbf= Wood controlsAdjust to conditions with wood capacity governing:

np 2= number of plates

P' P np CM Ct:= 2005 NDS (13.2.1) + Table 10.3.1

ASD LRFD

CD P' 39357.6 lbf= z KF P' 59139.072 lbf= OK

Capacity

Locate connection area - check end and edge distances from 13.3.2

ap 3in:= End distanceep 1in:= Rivet-to-wood edge distanceeps 0.5in:= Rivet-to-steel edge distance (Appendix M)

Determine the maximum number of rows with spacing: sq 1in:=nR

d 2 epsq

1+:= nR 8=

Try 8 rows of 10 rivets each side, spaced at 1" parallel to grain.

Wood - From Table 13.2.1A (Table Pw values are "per plate" each side; will need to double table value for total capacity of the connection - do it after determining which capacity controls):

sp 1in:=

b 3 in= member thicknessPw 21390lbf:=

Rivet - Equation 13.2-1 (Pr is "per plate", also will need to double table value for total capacity of the connection - do it after determining which capacity controls)

penetration = rivet length - plate thickness - 1/8"

plr tp 0.125in( )

in:=


< 1.0 OKTfPr

0.543=ftFt

0.543=

Ft 21.6ksi=Ft 0.6 Fy:=

Pr 48.6kips=Pr Fy Ag:=ft 11.733 ksi=ft TAg:=

LRFD (D1-1)ASDASD (D1)

Ag 1.5 in2=Ag tp bp:=

Gross Area Check - Yielding

v 0.75:= 0.9:=LRFDASDbp 8in:=Plate width:Fu 60ksi:=Fy 36ksi:=Plate material - Steel:

Plate - check plate for yield in tension in the various modes. We will use AISC's Manual of Steel Construction provisions to do this (ASD 9th Edition; LRFD 2nd Edition).

< 1.0 OKTf

z KF P'( ) 0.446=T

CD P'( ) 0.447=Demand - Capacity Ratios


Additional check to do:- member tension capacity

< 1.0 OKTfPr

0.573=TFt

0.573=

Pr 46.09 kips=Ft 30.727 kips=Pr v 0.6 Fu Anv v Fu Ant+:=Ft 0.3 Fu Anv 0.5 Fu Ant+:=

LRFD (J4-3a)ASDASD (J4)

Ant 0.943 in2=Ant tp bp 2 eps( ) nR 1( ) hp :=

Anv 0.135 in2=Anv 2 tp eps 0.5 hp( ):=

Net Section Check 1 - Tension Fracture

Ae tp bp hp nR( ):= Ae 1.078 in2=ASD (J4)ASD LRFD (D1-2)

ftTAe

:= ft 16.325 ksi= Pr v Fu Ae:= Pr 48.516 kips=

Ft 0.5 Fu:= Ft 30 ksi=

ftFt

0.544= TfPr

0.544= < 1.0 OK

Net Section Check 2 - Block Shear Fracture


Figure 4Example 2: Timber Rivets - ASD & LRFDDesign the beam hanger connection shown using timber rivets. The glulam beam and girder are untreated Douglas Fir glulam. The factored beam reaction is due to dead plus snow loads, and service conditions are wet. Use 2-1/2 inch rivets and 1/4" plate, and 2005 NDS provisions. Note that the designer must also confirm the bearing area for the roof beam support, and consider possible uplift conditions in the design of this connection.


R D S+:= Rf 1.2D 1.6S+:=R 5995 lbf= Rf 8992 lbf=

Capacity

Assume two rows in each plate, each side of hanger: sp 1in:=nR 2:=

Trial 1 - Try 8 rivets each row, spaced at 1" perpendicular to grain.

sq 1in:=nc 8:=

Wood - From Table 13.2.2A (load on wood is perpendicular to grain):

qw 1173lbf:=Locate connection and check end and edge distances from Table 13.3.2

nR 2= ap 3in:= End distance parallel to grainaq 2in:= End distance perp to grainep 1in:= Rivet-to-unloaded wood edge distanceeps 0.5in:= Rivet-to-steel edge distance (Appendix M)eq 2in:= Rivet-to-loaded wood edge distance

Wood: bbeam 5.125in:= Rivet/Plate: lr 2.5in:=dbeam 13.5in:= tp 0.25in:=

np 2:= (treat hanger face as two plates, separated by carried beam)

Modification factors (Table 10.3.1):

CD 1.15:= Load Duration / Time Effect (ASD - Table 10.3.2, LRFD - Table N3)Snow Load

0.8:=z 0.65:=

KF2.16z

:= KF 3.323=CM 0.8:= Wet service (Table 10.3.3)Ct 1.0:= Less than 100 deg F (Table 10.3.4)Cst 1.0:= 0.25" steel plate (Table 13.2.3)

Demand ASD LRFDD 1500lbf:=S 4495lbf:=


Q 2829.822 lbf= Wood controlsAdjust to conditions with wood capacity governing (Table 10.3.1, Footnotes 4 and 6):

np 2= number of platesQ' Q np CM Ct:=

ASD LRFD

Q' CD 5206.872 lbf= z KF Q' 7823.891 lbf=

Demand - Capacity Ratios (Trial 1)R

Q' CD( ) 1.151=Rf

z KF Q'( ) 1.149= > 1.0 NG

Try again - increase to 10 rivets per row


sq 1in:=nc 10:=

We choose to locate the rivet group into the girder near the center of the girder face, thus:

ep dbeam eps sq nc 1( ):= ep 6 in=ep

nc 1( ) sq 0.857=C 1.32:= (Table 13.2.2B interpolated)


plr tp 0.125in( )

in:= p 2.125=

Qw qw p0.8 C:= Qw 2829.822 lbf= 2005 NDS (13.2-3)

Rivet - from Equation 13.2-2

Qr 160 p0.32 nR nc lbf:= Qr 3258.328 lbf= 2005 NDS (13.2-2)

Take the minimum of wood or rivet capacity:

Q min Qw Qr,( ):=


z KF Q' 11260.782 lbf=Q' 6516.656 lbf=LRFDASD

Q' Q np CM Ct Cst:=number of platesnp 2=

Adjust to conditions with rivet capacity governing (Table 10.3.1, Footnotes 4 and 5). Note that CD drops out of the ASD capacity when rivet yield controls (Footnote 4), yet remains on the LRFD side. For LRFD, the time effect factor, , applies to Pr and Qr since the format conversion factor, KF, for connections adjusts from a 10-year to a 10-minute load basis. CD does not apply for ASD values of Pr and Qr (Footnote 4) because "rivet bending capacity" was treated as a steel limit state in early research and implementation. The early assumption was that rivet bending capacity is unaffected by load duration. Load duration effects were specifically considered in checks of wood strength limit states, not steel strength limit states.

Rivet controlsQ 4072.91 lbf=Q min Qw Qr,( ):=Take the minimum of wood or rivet capacity:

2005 NDS (13.2-2)Qr 4072.91 lbf=Qr 160 p0.32 nR nc lbf:=

Rivet - Equation 13.2-2

2005 NDS (13.2-3)Qw 8792.157 lbf=Qw qw p0.8 C:=

p 2.125=p lr tp 0.125in( )in

:=


(Table 13.2.2B interpolated)C 3.65:=

epnc 1( ) sq 0.444=

ep 4 in=ep dbeam eps sq nc 1( ):=Rivet to steel edge distanceeps 0.5in:=

qw 1318lbf:=

Wood - From Table 13.2.2A:


Demand - Capacity Ratios (Trial 2)RQ'( )

0.92= Rf z KF Q'( ) 0.799= < 1.0 OKTentative Solution

Refinement

To reduce tension perpendicular stresses from connectors placed in the middle of the side of the girder, just as for larger fasteners, it is good practice to "hang" the load from the top of the girder. This has additional benefits in terms of the number of rivets required, and ductility. We proceed with relocating the girder rivets closer to the top of the girder as shown below.


Rf 8992 lbf=R 5995 lbf=Rf 1.2D 1.6S+:=R D S+:=

S 4495lbf:=D 1500lbf:=

LRFDASDDemand

0.25" steel plate (Table 13.2.3)Cst 1.0:=Less than 100 deg F (Table 10.3.4)Ct 1.0:=Wet service (Table 10.3.3)CM 0.8:=

KF 3.323=KF 2.16z:=

z 0.65:= 0.8:=Load Duration / Time Effect

(ASD - Table 10.3.2, LRFD - Table N3)Snow Load

CD 1.15:=Modification factors (Table 10.3.1):

(treat hanger face as two plates, separated by carried beam)

np 2:=tp 0.25in:=dbeam 13.5in:=lr 2.5in:=Rivet/Plate:bbeam 5.125in:=Wood:


eq 2in:= Rivet-to-loaded wood edge distance

epnc 1( ) sq 0.111=

C 5.48:= (Table 13.2.2B interpolated)


plr tp 0.125in( )

in:= p 2.125=

Qw qw p0.8 C:= Qw 11748.048 lbf= 2005 NDS (13.2-3)

Rivet - from Equation 13.2-2

Qr 160 p0.32 nR nc lbf:= Qr 4072.91 lbf= 2005 NDS (13.2-2)


Q min Qw Qr,( ):= Q 4072.91 lbf= Rivet controls

Capacity

Assume two rows in each plate, each side of hanger: sp 1in:=nR 2:=


sq 1in:=nc 10:=

Wood - From Table 13.2.2A (load on wood is perpendicular to grain):

qw 1173lbf:=

Locate connection and check end and edge distances from Table 13.3.2

nR 2= ap 3in:= End distance parallel to grainaq 2in:= End distance perp to grainep 1in:= Rivet-to-unloaded wood edge distanceeps 0.5in:= Rivet-to-steel edge distance (Appendix M)


Adjust to conditions with rivet capacity governing (Table 10.3.1, Footnotes 4 and 6), remembering to drop the CD out of the ASD capacity when rivet yield controls (Footnote 4):

np 2= number of platesQ' Q np CM Ct:=

ASD LRFD

Q' 6516.656 lbf= z KF Q' 11260.782 lbf=Demand - Capacity Ratios (Trial 3)

RQ'

0.92= Rf z KF Q'( ) 0.799= < 1.0 OK

Solution


D 1.2:=Cst 1.0:= 3/8" steel plate (Table 13.2.3) W 1.6:=

Demand ASD LRFD

MD 100kip ft:= D MD 120 kip ft=MW 300kip ft:= W MW 480 kip ft=

DMD

dbeam:= D 17.143 kip=

WMWdbeam

:= W 51.429 kip=

T D W+:= Tf DD WW+:=T 68.571 kip= Tf 102.857kip=

Figure 5Example 3: Moment Connection with Timber Rivets - ASD & LRFDA three-pinned arch spanning 300 feet is built using 12-1/4" x 70" 24F-V8 Douglas Fir glulam. Each half-arch is to be spliced at the mid-point for shipping. Design the splice to resist a 400 k-ft moment due to wind 300 k-ft) and dead (100 k-ft) loading. Ignore axial and shear loads. Use 2005 NDS provisions.

Wood: bbeam 12.25in:= Rivet/Plate: lr 3.5in:=dbeam 70in:= tp 0.375in:=

Modification factors (Table 10.3.1):

CD 1.6:= Load Duration / Time Effect Factor(ASD Table 2.3.2, LRFD Table N3)Wind Load

1.0:=z 0.65:=

KF2.16z

:= KF 3.323=CM 0.8:= Wet service (Table 10.3.3)Ct 1.0:= Less than 100 deg F (Table 10.3.4)


nR 10=nc 18:=

Pr 280 p0.32 nR nc lbf:= Pr 71632.373 lbf= 2005 NDS (13.2-1)


P min Pw Pr,( ):= P 35650 lbf= Wood controlsAdjust to conditions with wood capacity governing:

np 1= number of platesP' P np CM Ct Cst:= 2005 NDS 13.2.1 + Table 10.3.1

ASD LRFD

CD P' 45.632 kip= z KF P' 61.603 kip=Rtop CD P':= RFtop z KF P':=

STEP 1: Capacity - Top Plate np 1:=Assume 3/8" top plate with 3 1/2" rivets: sp 1in:=nRmax

bbeam 1in 1in( )1in

:= nRmax 10.25= Use nR 10:=

Trial 1 - Try 10 rows, 18 rivets each row, spaced at 1" perpendicular to grain.

sq 1in:=nc 18:=

Wood - From Table 13.2.1E (Pw values are needed for one plate on one side only - see table footnote):

2 dbeam 140 in= Member thickness per Table 13.2.1E footnotePw 35650lbf:= 2005 NDS Table 13.2.1E

Rivet - Equation 13.2-1 (Pr is "per plate")penetration = rivet length - plate thickness - 1/8"

plr tp 0.125in( )

in:= p 3=


e2 dbeam 2PlateWidth

2lr+ 1in+

:= e2 43 in=

ASD LRFD

TsideMD MW+ Rtop e1( )

e2:= Tfside

D MD W MW+ RFtop e1( )e2

:=Tside 37.343 kip= Tfside 67.158 kip=

Trial 1 - Try 4 rivets each of 16 rows, spaced at 1" perpendicular to grain.

sp 1in:=nRmax

PlateWidth 1in 1in( )1in

:= nRmax 16= Use: nR 16:=sq 1in:=nc 4:=np 2:= number of plates

Demand - Capacity Ratios

TRtop( ) 1.503=

TfRFtop( ) 1.67= > 1.0 NG - GET additional capacity

from plates on beam sides

Check end and edge distances from 13.3.2

nR 10= ap 4in:= End distanceep 1in:= Rivet to wood edge distanceeps 0.5in:= Rivet to steel edge distance (Appendix M)

STEP 2: Capacity - Beam Side Plates

Provide additonal capacity for remaining moment resistance using rivet groups on both sides of beam.

Assume 18"wide x 3/8"thick plates each side with 3 1/2" rivets:

PlateWidth 18in:=e1 dbeam:= e1 70 in=



P min Pw Pr,( ):= P 25469.288 lbf= Rivet controls

Adjust to conditions with wood capacity governing:

np 2= number of platesP' P np CM Ct Cst:= 2005 NDS 13.2.1 + Table 10.3.1

ASD LRFD

P' 40.751 kip= z KF P' 88.022 kip=Rsides P':= RFsides z KF P':=

Demand - Capacity Ratios

MD MW+Rtop e1 Rsides e2+( ) 0.97=

D MD W MW+RFtop e1 RFsides e2+( ) 0.889= < 1.0 OK

Wood - From Table 13.2.1E (Pw is "per plate"):

Member thickness bbeam 12.25 in=Table interpolation: thickness1 10.5in:= rivetCapacity1 39900lbf:=

thickness2 12.5in:= rivetCapacity2 43880lbf:=

Pw rivetCapacity1bbeam thickness1( )

thickness2 thickness1( )

rivetCapacity1 rivetCapacity2( ):=

Pw 43382.5 lbf= 2005 NDS Table 13.2.1E

Rivet - Equation 13.2-1 (Pr is "per plate")penetration = rivet length - plate thickness - 1/8"

plr tp 0.125in( )

in:= p 3=

nR 16=nc 4=Pr 280 p

0.32 nR nc lbf:= Pr 25469.288 lbf= 2005 NDS (13.2-1)


Check end and edge distances from 13.3.2

nR 16= ap 7in:= End distance - 8" provided, OK

ep 1in:= Rivet to wood edge distance - increased to allow for top rivets.

eps 1in:= Rivet to steel edge distance ( > 1/2" minimum, Appendix M)

SolutionAs a final thought, there is extra capacity in the side plate design, so one more iteration would be useful to optimize the number of rivets for perhaps a narrower side plate width.


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Text2:

Text1: continued

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