Refined dynamic progressive collapse analysis of RC structures

Post-earthquake field investigation has revealed that if reinforced concrete (RC) structures in seismic regions were not designed to the level required by modern seismic design codes, they are vulnerable to severe damage or even progressive collapse when subjected to strong earthquakes. To gain insight into the mechanism and prevention of progressive collapse, it is imperative to develop an effective and efficient approach to capture the physical collapse of RC structures by numerical simulation. Finite element method (FEM)-based numerical simulation is one of the most widely used approaches for progressive collapse analysis, but some uncertainties still exist in its element removal algorithms. This paper refines FEM-based dynamic progressive collapse simulation for RC structures by introducing the concept of degree-of-freedom (DOF) release. With the concept, a RC beam-column element removal is a natural consequence of release of all DOFs of the element. This concept is implemented in an open-source finite element code of OpenSees. The test results of a RC beam with two ends fixed under a static load and a RC column with light transverse reinforcement under lateral pseudo-static load are first used to assess and demonstrate the advantages of the DOF release over the beam element removal. The refined progressive analysis method is then applied to a RC frame structure to demonstrate its dynamic progressive collapse with catenary effect included. Finally, a two-span continuous RC bridge with a two-column pier is taken as an example to demonstrate its flexure-shear-axial failure predicted by the proposed method.