DUCTILE DESIGN OF BEAM COLUMN JOINT

Abstract

The beam column joints in reinforced concrete frame building is the most critical part of the structure as the time when seismic forces act on the building, A large amount of forces attracted at beam column joints. Mostly, failure of structure is shear failure at joint and it is brittle nature. This type of failure not required as earthquake resistance design. For avoiding shear failure of joints IS Codes and different countries codes also, gives recommendation of beam and column joints in ductile frames that the joints must have adequate shear strength and ductility to facilitate the development of large inelastic reversible rotation in the event at the time of severe earthquake by providing this special confining reinforcement (hoops). This confining reinforcement near the column end should be extended in the join as well. Development length requirement for flexural reinforcement within the joint is also required. It is desirable to use high strength concrete mix in the joint region and shall achieve good compaction of concrete. The main problem at beam column joints is diagonal cracking and crushing of concrete. In the joint resign concrete may controlled by two means by providing large column sizes and closely spaced steel ties around column bar in the joint region. Ties are to hold the joint together and also resist the shear forces thereby reducing the cracking and crushing of concrete. We study Corner (knee) joint with the help of SAP and Staad model as finite Element Member and note the failure load, moments and deflection for two conditions, opening joint and closing joint. In another model we increased the area of concrete by providing 45 degree angle in the concrete fillet and provide nominal reinforcement. It is found that the moment, axial force and deflection are reduced. In third model, we increased concrete area by providing two fillet surfaces and again found moment, axial force and deflection are reduced. Fourth specimen same as third specimen, but we have provided extra reinforcement at tension side of opening joints. We have also verified experimentally by making four types of specimen and tested in the lab and found same results.