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Int. J. Struct. & Civil Engg. Res. 2013 xxxxxxxxxxxxxxxxxxxxx, 2013
SHEAR STRENGTH AND COLUMN DEPTH F0R RCBEAM COLUMN JOINT COMPARISION OF DRAFT
CODE WITH EURO CODE AND NZS CODE
Falak Parikh1* and Vimlesh Agarawal1
The behavior of reinforced concrete moment resisting frame structures in recent earthquakesall over the world has highlighted the consequences of poor performance of beam columnjoints. Large amount of research carried out to understand the complex mechanisms and safebehavior of beam column joints has gone into code recommendations. This paper presentscritical review of recommendations of well established codes regarding design column depthand shear strength aspects of beam column joints. The codes of practice considered are Draftcode IS13920-1993, NZS 3101: Part 1:1995 and the Euro code 8 of EN 1998-1:2003.
Keywords: Beam column joint; Code comparison; Reinforced concrete frame; Shear strength;Column depth; Nominal shear stress
1 SVIT, Vasad, Civil Engineering Department, xxxxxxxxxxxxxxxxxxxxxx.
*Corresponding Author: Falak Parikh,parikh40@gmail.com
ISSN 2319 – 6009 www.ijscer.comVol. 2, No. 3, August 2013
© 2013 IJSCER. All Rights Reserved
Int. J. Struct. & Civil Engg. Res. 2013
Research Paper
INTRODUCTIONBeam column joints in a reinforced concretemoment resisting frame are crucial zones fortransfer of loads effectively between theconnecting elements (i.e., beams andcolumns) in the structure. In normal designpractice for gravity loads, the design check forjoints is not critical and hence not warranted.But, the failure of reinforced concrete framesduring many earthquakes has demonstratedheavy distress due to shear in the joints thatculminated in the collapse of the structure.Detailed studies of joints for buildings inseismic regions have been undertaken only in
the past three to four decades. It is worthmentioning that the relevant researchoutcomes on beam column joints from differentcountries have led to conflicts in certainaspects of design. Coordinated programswere conducted by researchers from variouscountries to identify these conflicting issuesand resolve them. Nevertheless, it isimperative and informative to bring out thecritical aspects with respect to design ofseismic joints adopted by various internationalcodes of practice.
This paper presents a comprehensivereview of the design requirements of interior
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Int. J. Struct. & Civil Engg. Res. 2013 xxxxxxxxxxxxxxxxxxxxx, 2013
and exterior joints of special moment resistingreinforced concrete frames, with reference tothree codes of practices: American ConcreteInstitute (ACI 318M-02), New ZealandStandards (NZS 3101:1995) and Euro code8 (EN 1998-1:2003).
Member Sizes
In seismic conditions involving reversed cyclicloading, anchorage requirements assumegreat importance in deciding the sizes of themembers. This is because the limiting bondstress around the longitudinal bar is to besatisfied by the development length availablewithin the member.
Depth of Member for Interior Joint
In an interior joint, the force in a bar passingcontinuously through the joint changes fromcompression to tension. This causes push-pulleffect with distribution of bond stress as shownin Figure 1. The severe demand on bondstrength necessi tates that adequatedevelopment length for the bar to be madeavailable within the depth of the member. Inother words, for the longitudinal bar of thebeam the development length should beprovided by the column depth and vice versa.In recognition of this, the codes limit the ratiobetween the bar diameter and the member
Figure 1: Bond Conditionin an Interior Joint
depth. By adopting smaller diameter barswhich require reduced development length, thesizes of the members can be controlled.
NZS 3101:1995 gives the followingexpression relating the bar diameter and themember depth. The expression explicitlyinvolves the parameters that affect the bondperformance such as axial load, condition ofconcreting done near the bar and materialstrengths. The code suggests an expressionin the form of bar diameter to column depthratio as
0
'6 t p cb
fc s y
fd
h f
EN 1998-1: 2003 recommends anexpression similar to that in the NZS code byconsidering the effect of axial load, materialstrength and ratio of compression to tensionreinforcement. Anchorage of longitudinal barsfor interior beam column joints high ductilityclass (DCH) must satisfy the followingexpression:
'
max
7.5 1 0.8
1 0.75
b ctm d
c Rd ydd
d f v
h fk
And Draft code IS 19320-1993 columndepth value are require data for building.
Depth of Member for Exterior Joint
In exterior joints the beam longitudinalreinforcement that frames into the columnterminates within the joint core. Figure 2 showsthe typical anchoring of beam bars and thebond deterioration in an exterior joint. Theanchorage and development length of the barswithin the joint is usually defined with respect
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Int. J. Struct. & Civil Engg. Res. 2013 xxxxxxxxxxxxxxxxxxxxx, 2013
to a critical section located at a distance fromthe column face where the bars enter into thejoint. The critical section refers to the sectionfrom where the development length would beconsidered effective and not affected by yieldpenetration and deterioration of bond.
NZS 3101:1995 gives the expression ofhorizontal development length as
1 2 '0.24 y b
dh b
c
f dL
f
EN 1998-1:2003 expression for anchoragerequirements in the case of exterior joint is inthe form of beam bar diameter to column depthratio. It considers the effect of axial load onthe column. The following expression givesdirectly the required depth of column, hcinstead of horizontal development length, Ldh.
7.5(1 0.8 )b ctm
dc Rd yd
d fv
h f
Figure 2: Details of Exterior Joint
And Draft code IS 19320-1993 columndepth value are require data for building.
Nominal Shear Stress and Strengthof the Joint
The level of shear stress, as expressed bynominal shear stress, is an important factoraffecting both strength and stiffness of the joint.The codes restrict the nominal shear stress tobe less than a fraction of compressive strengthof concrete. All three codes evaluate thenominal shear capacity based on strutmechanism and express it as a function ofconcrete strength irrespective of the amountof shear reinforcement. However, the nominalshear capacity is influenced by theconfinement provided by the adjoiningmembers. A beam member that frames into a
face is considered to provide confinement tothe joint if at least the framing member covers
three quarters of the joint.
The NZS 3101:1995 has developed
recommendations considering contributions
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Int. J. Struct. & Civil Engg. Res. 2013 xxxxxxxxxxxxxxxxxxxxx, 2013
from strut and truss mechanisms and hassuggested a limiting value of 0.2 f
c’ , with
respect to strut mechanism irrespective of theconfinement offered by the framing members.And shear strength equation.
0.2 'c jf A
EN 1998-1:2003 also has limited the
nominal shear stress and shear strength, vjh
within interior beam column joint to be less thanthe stress value given by the expression
1 djh cd
vV f
And 1 d
jh cd j
vV f A
Draft code IS 13920-1993 nominal shearstress and shear strength equation
Building Details
STAAD – Pro-Model Rendered View
please chktable nosandheadingsand theyare notmentionedin the text
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Int. J. Struct. & Civil Engg. Res. 2013 xxxxxxxxxxxxxxxxxxxxx, 2013
1.2 'cf and 1.2 'c jf A
Data of Building
WallsOuter periphery walls thickness = 230 mm
Inner wall thickness = 115mm
Beams230 mm X 300 mm size at the level 3 to 5
230 mm X 570 mm size at level – 2
ColumnColumn CA = 380mmX380mm
Column CB = 460mmX300mm
Column Cc = 300mmX460mm
Slab
All Slabs 120 mm thick
Live Load
4 kN/mm2 at typical floors.
2 kN/mm2 at roof level.
1 kN/mm2 floor finish.
Yield Strength of steel= 415 N/mm2
Interior Joint Column Depth
Comparison of column depth along differentdiameter
(here M 20 Grade use)
Diameter IS:13920 NZS EN
12 300 522.897 544.911
16 300 697.196 726.548
20 300 871.495 908.184
25 300 1089.368 1135.231
32 300 1394.391 1453.095
Note: All dimension in mm.
Figure 3: Bar Dia Vs. Column Depth
fck IS 13920 NZS EN
20 300 1089.368 1135.231
25 300 974.361 979.761
30 300 889.465 868.474
40 300 770.300 717.772
50 300 688.977 618.994
Note: All dimension in mm.
Comparison of Column DepthAlong Different Concrete Strength
(here 25 diameter use)
Figure 4: Concrete StrengthVs Column Depth
EXTERIOR JOINT COLUMNDEPTHComparison of Column DepthAlong Different Diameter
(here M 20 Grade use)
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Int. J. Struct. & Civil Engg. Res. 2013 xxxxxxxxxxxxxxxxxxxxx, 2013
Diameter IS:13920 NZS EN
12 380 227.167 355.779
16 380 302.889 474.371
20 380 378.611 592.964
25 380 473.264 741.205
32 380 605.778 948.743
Note: All dimension in mm.
Figure 5: Concrete Strength Vs.Column Depth
NOMINAL SHEAR STRESS OFJOINTInterior Joint Nominal Shear Stress
Effect of Concrete Strength ofNominal Shear Stress
Exterior joint Nominal Shear Stress
Effect of concrete strength ofNominal shear stress
fc' IS:13920 NZS EN
20 5.367 4.000 5.877
25 6.000 5.000 7.141
30 6.573 6.000 8.323
40 7.589 8.000 10.438
50 8.485 10.000 12.220
Figure 6: Concrete Strength Vs.Nominal Shear Stress
fc' IS:13920 NZS EN
20 4.472 4.000 4.702
25 5.000 5.000 5.713
30 5.477 6.000 6.658
40 6.325 8.000 8.350
50 7.071 10.000 9.776
Figure 7: Concrete Strength Vs.Nominal Shear Stress
NOMINAL SHEAR STRENGTHNominal Shear Strength of interiorjoint
Effect of Concrete Strength ofNominal shear strength
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Int. J. Struct. & Civil Engg. Res. 2013 xxxxxxxxxxxxxxxxxxxxx, 2013
fc' IS:13920 NZS EN
20 611.788 456.000 670.015
25 684.000 570.000 814.123
30 749.284 684.000 948.831
40 865.199 912.000 1189.942
50 967.322 1140.000 1393.103
Figure 8: Concrete Strength Vs.Nominal Shear Strength
Nominal Shear Strength of exteriorjoint:
Effect of Concrete Strength ofNominal Shear Strength
fc' IS:13920 NZS EN
20 645.776 577.600 678.948
25 722.000 722.000 824.978
30 790.911 866.400 961.482
40 913.266 1155.200 1205.807
50 1021.062 1444.000 1411.678
Figure 10: Concrete Strength Vs.Nominal Shear Strength
SUMMARY ANDCONCLUSION
The behavior and expected performance offlexural members of reinforced concretemoment resisting frames can be realizedonly when the joints are strong enough tosustain the severe forces set up underlateral loads. Hence, the design anddetailing of joints is critical, especially inseismic conditions. A comprehensivediscussion of the issues and recommendedprocedures to be considered in the designof joints has been presented. The designaspects covered by Draft code 13920-1993, NZS 3101:1995 and EN 1998-1:2003 international codes of practice areappraised and compared.
• Draft code 13920-1993 requires smallercolumn depth as compared to the other twocodes for satisfying the anchorageconditions for interior and exterior joints. Theeffect of higher concrete grade in reducingthe column depth has been included in EN1998-1:2003 and NZS 3101:1995. Therequirement on the depth of column ininterior joint is more compared to that inexterior joint.
• The criteria for minimum flexural strength ofcolumns required to avoid soft storeymechanism is very stringent as per NZS3101:1995 while the other two codesrecommendations are comparable.
REFERENCES1. A book “Design Of Concrete Structur II”
2. Chang-Ming Lin and Jose I .Restrepo(2000), “Evolution of The Shear Strengthof Beam Column Joints of Reinforced
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Int. J. Struct. & Civil Engg. Res. 2013 xxxxxxxxxxxxxxxxxxxxx, 2013
Concrete Frames Subjected To TheEarthquake Loading”.
3. Cheng-Ming Lin and Jose I Restrepo(2002), “Seismic Behaviour And Designof Reinforced Concrete Interior BeamColumn Joint” Bulletin of The NewZealand Society For EarthquakeEngineering”, Vol. 35, No. 2.
4.Uma S R and Sudhir K Jain, “SeismicBehavior Of Beam Column Joints InReinforced Concrete Moment ResistingFrame A Review Of Code”, IITK-GSDMA-EQ32-V 1.0.
5. Uma S R and Meher Prasad A, “SeismicBehavior Of Beam Column Joints InReinforced Concrete Moment ResistingFrame”, IITK-GSDMA-EQ31-V 1.0.
6. Hitoshi Shiohara (2004), ”QuadrupleFlexural Resistance in R/C Beam ColumnJoints”, 13th World Conference onEarthquake Engineering, Vancouver , BCCanada, August, Paper No. 491.
7. Ibrahim G. Shaaban and Maher A. Adam(2008), ”Seismic Behavior of Beam
Column Connection In High StrengthBuilding Concrete Frame”.
8. Kazuhiro Kitayama, Shunsuke Otani andHiroyuki Aoyama (1987), “EarthquakeResistance Design Cri teria ForReinforced Concrete Interior BeamColumn Joint”, This paper was publishedin the Proceedings, Pacific Conferenceon Earthquake Engineering, Wairakei,New Zealand, August 5 - 8, Vol. 1, pp.315-326.
9. Kuzuhiro Kityamaha, Shunsuke Otani,Hiroyuki Aoyama (1991), “Developmentfor Design Criteria for RC Interior BeamColumn Joint”.
10. Subramanian N and Prakash Rao D S(2003), “Design of Joints in RC StructuresWith Particular Reference to SeismicConditions”, The Indian ConcreteGeneral, February.
11. Patil Yogesh .D, Patil H S, Raju M N K A,“Effect of Key Parameters On TheSeismic Design Of Reinforced ConcreteFrame Joint”, November.
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