shear strength and column depth f0r rc beam column …€¦ · · 2015-04-29shear strength and...

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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,[email protected]

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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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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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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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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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


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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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


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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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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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.

shear strength and column depth f0r rc beam column …€¦ · · 2015-04-29shear strength and...

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