Bond slip in reinforced concrete beam-column joints- a semi-empirical implicit modeling and possible influence of design standard compliance

Abstract

Bond slip in RC beam-column joints may affect the seismic response or performance assessment of structures considerably. Explicit macroscopic models that satisfy the joint kinematics can be incorporated within a frame model to numerically account for the effect of bond slip. Seismic performance assessment of buildings generally rules out the explicit modeling owing to the associated computational cost. Simplified implicit models are instead preferred owing to the ease of implementation in a commercial finite element (FE) provided the model parameters are calibrated experimentally. Extrapolation of the calibration is generally not valid in other cases with different geometry, sizes and even loading protocols. Most commercial software do not offer the features to explicitly modeling the bond slip. Numerical modeling of bond slip is proposed in this paper that can be conveniently implemented in a commercial software such as Seismostruct. Unlike the prior art, the slip parameter can be extracted using a semiempirical approach preceded by the generation of a numerical database. The proposed framework is also validated against the experimental results of one exterior and one interior beam-column joints. Sample illustration on an example building designed against the same seismic hazard level but following the recommendations per IS 13920, ACI 318 and EC8 is considered for monotonic (without bond slip) and cyclic (with bond slip) pushover analyses. Consideration of bond slip initiates early yielding and results in reduction of secant stiffness at the onset of yielding. The extent of influence depends on the compliance of design standards. For example, relatively higher percentage of reinforcement when designed per IS 13920 (as compared to ACI 318 and EC8) leads to a somewhat lower slip parameter resulting in lesser yield displacement and reduction of secant stiffness at the onset of yielding.