SHEAR STRENGTH AND COLUMN DEPTH F0R RC BEAM COLUMN JOINT COMPARISION OF DRAFT CODE WITH EURO CODE AND NZS CODE

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1 Int. J. Struct. & Civil Engg. Res xxxxxxxxxxxxxxxxxxxxx, 2013 Research Paper ISSN Vol. 2, No. 3, August IJSCER. All Rights Reserve SHEAR STRENGTH AND COLUMN DEPTH F0R RC BEAM COLUMN JOINT COMPARISION OF DRAFT CODE WITH EURO CODE AND NZS CODE Falak Parikh 1 * an Vimlesh Agarawal 1 *Corresponing Author: Falak Parikh, parikh40@gmail.com The behavior o reinorce concrete moment resisting rame structures in recent earthquakes all over the worl has highlighte the consequences o poor perormance o beam column joints. Large amount o research carrie out to unerstan the complex mechanisms an sae behavior o beam column joints has gone into coe recommenations. This paper presents critical review o recommenations o well establishe coes regaring esign column epth an shear strength aspects o beam column joints. The coes o practice consiere are Drat coe IS , NZS 3101: Part 1:1995 an the Euro coe 8 o EN :2003. Keywors: Beam column joint; Coe comparison; Reinorce concrete rame; Shear strength; Column epth; Nominal shear stress INTRODUCTION Beam column joints in a reinorce concrete moment resisting rame are crucial zones or transer o loas eectively between the connecting elements (i.e., beams an columns) in the structure. In normal esign practice or gravity loas, the esign check or joints is not critical an hence not warrante. But, the ailure o reinorce concrete rames uring many earthquakes has emonstrate heavy istress ue to shear in the joints that culminate in the collapse o the structure. Detaile stuies o joints or builings in seismic regions have been unertaken only in the past three to our ecaes. It is worth mentioning that the relevant research outcomes on beam column joints rom ierent countries have le to conlicts in certain aspects o esign. Coorinate programs were conucte by researchers rom various countries to ientiy these conlicting issues an resolve them. Nevertheless, it is imperative an inormative to bring out the critical aspects with respect to esign o seismic joints aopte by various international coes o practice. This paper presents a comprehensive review o the esign requirements o interior 1 SVIT, Vasa, Civil Engineering Department, xxxxxxxxxxxxxxxxxxxxxx. 14

2 an exterior joints o special moment resisting reinorce concrete rames, with reerence to three coes o practices: American Concrete Institute (ACI 318M-02), New Zealan Stanars (NZS 3101:1995) an Euro coe 8 (EN :2003). Member Sizes In seismic conitions involving reverse cyclic loaing, anchorage requirements assume great importance in eciing the sizes o the members. This is because the limiting bon stress aroun the longituinal bar is to be satisie by the evelopment length available within the member. Depth o Member or Interior Joint In an interior joint, the orce in a bar passing continuously through the joint changes rom compression to tension. This causes push-pull eect with istribution o bon stress as shown in Figure 1. The severe eman on bon strength necessitates that aequate evelopment length or the bar to be mae available within the epth o the member. In other wors, or the longituinal bar o the beam the evelopment length shoul be provie by the column epth an vice versa. In recognition o this, the coes limit the ratio between the bar iameter an the member Figure 1: Bon Conition in an Interior Joint epth. By aopting smaller iameter bars which require reuce evelopment length, the sizes o the members can be controlle. NZS 3101:1995 gives the ollowing expression relating the bar iameter an the member epth. The expression explicitly involves the parameters that aect the bon perormance such as axial loa, conition o concreting one near the bar an material strengths. The coe suggests an expression in the orm o bar iameter to column epth ratio as h 6 b t p c c s 0 y EN : 2003 recommens an expression similar to that in the NZS coe by consiering the eect o axial loa, material strength an ratio o compression to tension reinorcement. Anchorage o longituinal bars or interior beam column joints high uctility class (DCH) must satisy the ollowing expression: b 7.5 ctm 1 0.8v ' hc R y k ' max An Drat coe IS column epth value are require ata or builing. Depth o Member or Exterior Joint In exterior joints the beam longituinal reinorcement that rames into the column terminates within the joint core. Figure 2 shows the typical anchoring o beam bars an the bon eterioration in an exterior joint. The anchorage an evelopment length o the bars within the joint is usually eine with respect 15

3 to a critical section locate at a istance rom the column ace where the bars enter into the joint. The critical section reers to the section rom where the evelopment length woul be consiere eective an not aecte by yiel penetration an eterioration o bon. NZS 3101:1995 gives the expression o horizontal evelopment length as L h y 0.24 b1 2 b ' c EN :2003 expression or anchorage requirements in the case o exterior joint is in the orm o beam bar iameter to column epth ratio. It consiers the eect o axial loa on the column. The ollowing expression gives irectly the require epth o column, hc instea o horizontal evelopment length, Lh. h b 7.5 ctm c R y (1 0.8 v ) An Drat coe IS column epth value are require ata or builing. Nominal Shear Stress an Strength o the Joint The level o shear stress, as expresse by nominal shear stress, is an important actor aecting both strength an stiness o the joint. The coes restrict the nominal shear stress to be less than a raction o compressive strength o concrete. All three coes evaluate the nominal shear capacity base on strut mechanism an express it as a unction o concrete strength irrespective o the amount o shear reinorcement. However, the nominal shear capacity is inluence by the coninement provie by the ajoining members. A beam member that rames into a ace is consiere to provie coninement to the joint i at least the raming member covers three quarters o the joint. The NZS 3101:1995 has evelope recommenations consiering contributions Figure 2: Details o Exterior Joint 16

4 p t a h a a m i Int. J. Struct. & Civil Engg. Res xxxxxxxxxxxxxxxxxxxxx, 2013 rom strut an truss mechanisms an has suggeste a limiting value o 0.2 c, with respect to strut mechanism irrespective o the coninement oere by the raming members. An shear strength equation. 0.2 ' A c j EN :2003 also has limite the nominal shear stress an shear strength, v jh within interior beam column joint to be less than the stress value given by the expression V v v V A jh c 1 An jh c 1 j Drat coe IS nominal shear stress an shear strength equation Builing Details STAAD Pro-Moel Renere View 17

5 1.2 c ' an 1.2 c ' A j Figure 3: Bar Dia Vs. Column Depth Data o Builing Walls Outer periphery walls thickness = 230 mm Inner wall thickness = 115mm Beams 230 mm X 300 mm size at the level 3 to mm X 570 mm size at level 2 Column Column CA = 380mmX380mm Column CB = 460mmX300mm Column Cc = 300mmX460mm Slab All Slabs 120 mm thick Live Loa 4 kn/mm 2 at typical loors. 2 kn/mm 2 at roo level. 1 kn/mm 2 loor inish. Yiel Strength o steel= 415 N/mm 2 Interior Joint Column Depth Comparison o column epth along ierent iameter Comparison o Column Depth Along Dierent Concrete Strength (here 25 iameter use) ck IS NZS EN Note: All imension in mm. Figure 4: Concrete Strength Vs Column Depth (here M 20 Grae use) Diameter IS:13920 NZS EN Note: All imension in mm. EXTERIOR JOINT COLUMN DEPTH Comparison o Column Depth Along Dierent Diameter (here M 20 Grae use) 18

6 Diameter IS:13920 NZS EN Figure 6: Concrete Strength Vs. Nominal Shear Stress Note: All imension in mm. Figure 5: Concrete Strength Vs. Column Depth c' IS:13920 NZS EN NOMINAL SHEAR STRESS OF JOINT Interior Joint Nominal Shear Stress Eect o Concrete Strength o Nominal Shear Stress Exterior joint Nominal Shear Stress Eect o concrete strength o Nominal shear stress Figure 7: Concrete Strength Vs. Nominal Shear Stress c' IS:13920 NZS EN NOMINAL SHEAR STRENGTH Nominal Shear Strength o interior joint Eect o Concrete Strength o Nominal shear strength 19

7 c' IS:13920 NZS EN Figure 8: Concrete Strength Vs. Nominal Shear Strength Nominal Shear Strength o exterior joint: Eect o Concrete Strength o Nominal Shear Strength c' IS:13920 NZS EN Figure 10: Concrete Strength Vs. Nominal Shear Strength SUMMARY AND CONCLUSION The behavior an expecte perormance o lexural members o reinorce concrete moment resisting rames can be realize only when the joints are strong enough to sustain the severe orces set up uner lateral loas. Hence, the esign an etailing o joints is critical, especially in seismic conitions. A comprehensive iscussion o the issues an recommene proceures to be consiere in the esign o joints has been presente. The esign aspects covere by Drat coe , NZS 3101:1995 an EN :2003 international coes o practice are appraise an compare. Drat coe requires smaller column epth as compare to the other two coes or satisying the anchorage conitions or interior an exterior joints. The eect o higher concrete grae in reucing the column epth has been inclue in EN :2003 an NZS 3101:1995. The requirement on the epth o column in interior joint is more compare to that in exterior joint. The criteria or minimum lexural strength o columns require to avoi sot storey mechanism is very stringent as per NZS 3101:1995 while the other two coes recommenations are comparable. REFERENCES 1. A book Design O Concrete Structur II 2. Chang-Ming Lin an Jose I.Restrepo (2000), Evolution o The Shear Strength o Beam Column Joints o Reinorce 20

8 Concrete Frames Subjecte To The Earthquake Loaing. 3. Cheng-Ming Lin an Jose I Restrepo (2002), Seismic Behaviour An Design o Reinorce Concrete Interior Beam Column Joint Bulletin o The New Zealan Society For Earthquake Engineering, Vol. 35, No Uma S R an Suhir K Jain, Seismic Behavior O Beam Column Joints In Reinorce Concrete Moment Resisting Frame A Review O Coe, IITK- GSDMA-EQ32-V Uma S R an Meher Prasa A, Seismic Behavior O Beam Column Joints In Reinorce Concrete Moment Resisting Frame, IITK-GSDMA-EQ31-V Hitoshi Shiohara (2004), Quaruple Flexural Resistance in R/C Beam Column Joints, 13 th Worl Conerence on Earthquake Engineering, Vancouver, BC Canaa, August, Paper No Ibrahim G. Shaaban an Maher A. Aam (2008), Seismic Behavior o Beam Column Connection In High Strength Builing Concrete Frame. 8. Kazuhiro Kitayama, Shunsuke Otani an Hiroyuki Aoyama (1987), Earthquake Resistance Design Criteria For Reinorce Concrete Interior Beam Column Joint, This paper was publishe in the Proceeings, Paciic Conerence on Earthquake Engineering, Wairakei, New Zealan, August 5-8, Vol. 1, pp Kuzuhiro Kityamaha, Shunsuke Otani, Hiroyuki Aoyama (1991), Development or Design Criteria or RC Interior Beam Column Joint. 10. Subramanian N an Prakash Rao D S (2003), Design o Joints in RC Structures With Particular Reerence to Seismic Conitions, The Inian Concrete General, February. 11. Patil Yogesh.D, Patil H S, Raju M N K A, Eect o Key Parameters On The Seismic Design O Reinorce Concrete Frame Joint, November. 21