Experimental research on the progressive collapse resistance of concrete beam-column sub-assemblages reinforced with steel-FRP composite bar

Abstract

The progressive collapse behavior of conventional reinforced concrete frame structures caused by the loss of columns has been widely investigated over the past years. However, few papers on the improvement of the structural progressive collapse resistance accounting for the mechanical properties of the reinforcement material are reported. As a kind of reinforcement material of reinforced concrete frames, steel-FRP composite bar (SFCB) has the typical feature of controllable post-yield stiffness. This paper explored and compared the progressive collapse characteristics of concrete frames reinforced with SFCBs, steel bars and hybrid reinforcements including both steel bars and FRP bars. Scaled pushdown experiments based on the alternate load path method were conducted to study the effect of post-yield stiffness on the progressive collapse resistance of beam-column sub-assemblages. The experimental results demonstrated that the SFCB specimens experienced three mechanical actions: flexural action, post-yield stiffness plus compressive arch action (PYSCAA) and catenary action. The feature of the PYSCAA differed significantly from the second action of the specimen reinforced with steel bars. Due to the effect of the post-yield stiffness, not only was the load capacity of SFCB specimens significantly enhanced, but also the transition displacements from the PYSCAA to the catenary action were delayed. Meanwhile, the finite element method was employed to simulate the whole progressive collapse process of the specimens, and the simulation results agreed well with the experimental ones. Parametric analyses based on numerical simulations proved that the application of SFCBs was beneficial to reduce the vulnerability of progressive collapse for concrete frames. The ratio of post-yield modulus to initial elastic modulus of SFCBs was found to be the key factor affecting the characteristics of the progressive collapse resistance, and the optimal ratio of 0.30 is recommended.