Experimental investigation and 3D cyclic finite element simulation of R/C exterior beam-column joints retrofitted with CFRP composite materials

Abstract

The research presented attempts to develop carbon fiber reinforced polymer (CFRP) retrofitting techniques for improving existing reinforced concrete (R/C) beam-column joints designed for gravity loads only including common pre-1970’s seismically deficient steel reinforcement details. Full-scale experimental as well as numerical investigations are conducted to achieve the objectives of the research. The experimental study consisted of testing of twelve T-shaped beam-column joints including as-built, CFRP retrofitted and repaired and then CFRP retrofitted under constant column axial load and cyclic lateral loading reversals simulating an earthquake motion. The numerical investigation involved 3-D finite element (FE) simulations of as-built and CFRP retrofitted reinforced concrete beam-column joints under the similar loading and boundary conditions using explicit dynamic software, LS-Dyna. Effects of concrete cracking, shear transfer due to aggregate interlocking, three axial state of stress, complex behavior due to orthotropic property of the CFRP, asymmetric stress-strain relationships for tensile and compressive deformations of concrete and CFRP materials, concrete crushing, and CFRP rapture are included in the FE analyses. In the experimental study, as-built beam-column joint specimens failed due to excessive shear damage at the joint core and/or slippage of the shortly embedded beam bottom longitudinal reinforcement. Accordingly, three different CFRP retrofitting schemes were developed. The damage at the joint core and the slippage of shortly embedded beam positive reinforcement was substantially controlled due to the developed CFRP retrofitting. Finite Element (FE) simulation results were verified with the experimental findings. This provided additional understanding on the behavior and also proved that the explicit FE could be used as a tool for predicting the response of 3-D R/C beam-column joints under cyclic loadings.