Strain‐centric approach for design of confined core concrete in the columns of short and regular RC frames under cyclic tests

The cyclic testing of two full scale regular and short column irregular frames has been carried out under large deformations. The load‐deformation hysteresis behavior of the frames has been obtained along‐with strain‐deformation profile of the core concrete at the plasticized sections of the columns of the frames. The strain values of the core concrete are one of the direct criteria to the damage levels for plastic hinges of structural member as compared to stress or rotation. A strain based damage relationship is quantitatively defined on the basis of developed strain profile and plastic strain resisting capacity of confined core concrete. The developed strain profiles have been monitored and measured by the use of digital image correlation (DIC) technique. The plastic strain resisting capacity of confined core concrete has been determined separately under axial compression of cylindrical and square prismatic specimens with varying amount of volumetric ratio of transverse reinforcement. The strain based severity parameters, that is, strain hysteresis loop (principal strain versus displacement), permanent strain, strain resistance capacity and finally, character of strain angles have been compared to define the damages in the plastic hinged region of the frames.