STUDY ON THE IMPACT RESISTANCE OF DOUBLE-COLUMN CONCRETE-FILLED STEEL TUBULAR BRIDGE PIERS CONSIDERING THE SUPERSTRUCTURE MASS

Concrete-filled steel tubular (CFST) members combine the advantages of steel tube and core concrete, which has been gradually employed in bridge piers, and the impact resistance is a key issue to promote its application. For this purpose, a total of 56 finite element (FE) models of double-column CFST piers subjected to vehicle collision were established using LS-DYNA software, and mechanism analysis as well as parameter studies of impact resistance were performed. The FE models were verified by comparing with the data of the drop-hammer impact and the actual vehicle-impact test. The impact force, the plastic strain development, internal force distribution and energy conversion of typical CFST piers were investigated. The effects of steel ratio, axial-load ratio, cargo stiffness, vehicle mass and speed on the impact force and lateral-displacement distribution were analyzed. The equivalent static force method was used to calculate the 25 ms equivalent vehicle impact force (ESF₂₅), and then the recommended value of AASHTO code was evaluated. The equation for the impact force of CFST piers was proposed. The results showed that steel tubes and concrete can work together well under vehicle impact, and steel tubes are the main energy-absorbing component. Due to the existence of the upper mass and the inertial force, the internal force distribution of the piers corresponding to different impact phases is significantly different. Parametric studies indicated that the vehicle mass and speed have significant influences on the evolution of impact force, while the effects of steel ratio and axial load ratio are marginal. In addition, the Young’s modulus of cargo has an obvious effect when it varies within 2000 MPa. The proposed equation could well predict the impact force of CFST piers considering the influence of the upper mass.