Performance of the CFST column to composite beam connection under static and impact loads

Abstract

A progressive collapse of structures is usually triggered by extreme incidents, especially explosions and impacts, resulting in a dynamic response that differs from the conventional column removal scenario. However, the design solutions in the criteria may not be applicable for evaluating the progressive collapse resistance of structures under the impact load. To ascertain the influence of the high strain rate effect, a finite element (FE) study is conducted on the CFST column to composite beam connection under impact and static loads. The failure modes and resistance mechanisms for two types of composite connections under the two loads are compared. Moreover, the effects of different impact energies on the impact load, vertical deflection, vertical force, and energy dissipation are discussed by varying the impact mass and velocity. Finally, the dynamic increase factors (DIFs) based on force, deflection, and energy with various impact energies are investigated. It is found that the impact load is chiefly contributed by the inertia effect (IE) at initial loading stage and by the flexural action (FA) at large deformation stage. Interestingly, the vertical force for the connection under an impact loading is negative before the approximate plastic chord rotation (θy). Although the peak impact force, maximum vertical deflection, and energy absorption ratio all increase with the impact energy raised, the former is more sensitive to impact velocity, and the latter two are more sensitive to impact mass. Moreover, a series of findings from the study demonstrate that the DIFs based on force, deflection, and energy under the impact load are significantly different from the conventional dynamic load.