DUCTILITY FACTOR OF REINFORCED CONCRETE FRAME WITH WEAK BEAM-COLUMN JOINT

Abstract

Code requirements are usually fulfilled during the design of a building. On the other hand, reinforced concrete (RC) frames (particularly in the developing regions of the world) are found deficient due to unregulated constructions. Majority of such deficient structures lack shear reinforcement in beam-column joints. Collapse of these deficient buildings (as a result of limited ductility) triggered many socio-economic and human losses which is evident from recent earthquake disasters. This paper presents an experimental study which was conducted on a 1:4 reduced scale three-storey RC special moment resisting frame (SMRF) lacking shear reinforcement in the beam-column joints. The lack of confinement bars causes shear hinging of joints that reduces the displacement ductility of the frame. Shake-table tests were conducted on test model that was subjected to acceleration time history of 1994 Northridge earthquake, having a peak ground acceleration of 0.57g. The acceleration was linearly scaled to multiple levels and to sinusoidal base excitations of various frequencies and displacements. Moderate to severe damage at each storey level was observed in the joint panels due to the lack of lateral reinforcing ties in the joints. The data obtained from shake table tests were processed and analysed to develop a lateral force-deformation capacity curve, which was bi-linearized as an elasto-plastic curve to compute various response parameters of frame. The ductility factor (Rμ) of the tested model was found to be equal to 1.95, which is thirty-five percent less than the code recommended value of Rμ for RC SMRF structures.