Performance of FRP-strengthened reinforced concrete columns under impact loading

Abstract

The work presented herein focuses on studying experimentally and numerically the behaviour of RC columns under the combined action of axial and lateral static or impact loading, in particular when these members are strengthened with external sheets of Carbon Fiber Reinforced Polymers (CFRP). In total, twenty-five RC column specimens (un-strengthened and CFRP-strengthened) with identical dimensions have been tested. Each specimen was first axially loaded to a predefined level and then subject to a three point bending test during which a lateral concentrated load was applied at mid-span. The lateral load was applied either quasi-statically in the form of small increments up to the specimen’s failure or dynamically by dropping a steel mass from a predefined height. In the case of the un-strengthened specimens, the study mainly focused on examining the effect of axial loading on the behaviour of the RC columns under lateral impact. In the case of the strengthened specimens, the effect of different configurations of CFRP sheets used for strengthening on the response of RC columns under static and lateral impact loading was also investigated. The experimental results have shown that the CFRP wrapping provides confinement to the concrete which, in turn, reduces the sustained damage and increases the energy absorbed by the strengthened specimens. The ultimate and residual mid-span deflections decrease compared to those of the un-strengthened specimens indicating that the CFRP sheets increase the stiffness of RC columns. Furthermore, as a consequence of the smaller damage sustained by the strengthened specimens, the number of impact drops, which these specimens can sustain before failure, increases. In the numerical studies, a 3-dimensional finite element (FE) model has been developed using commercial software ABAQUS to simulate the static and impact behaviour of RC columns and validated using the experimental results. The Concrete Damage Plasticity (CDP) model has been adopted to describe the concrete properties. The numerical results have shown that the CDP model can predict reasonably well the response of RC columns, including the crack pattern, under static and impact loading.