A PROGRESSIVE COLLAPSE ANALYTICAL MODEL OF RC FRAME STRUCTURES BASED ON COROTATIONAL FORMULATION FOR FORCE-BASED FIBER ELEMENTS

Previous studies have shown that the catenary mechanism can bring RC frame structures additional load-bearing capacity to resist progressive collapse, and is essential to the progressive collapse resisting capacity of structures. The catenary mechanism occurs under the state of large geometric deformation and the material is in the nonlinear descent stage. Therefore, it is necessary to consider both material nonlinearity and geometric nonlinearity, which requires a more complicated numerical model. To co-process the material nonlinearity and geometric nonlinearity using fiber elements, a force interpolation fiber element based on co-rotational procedure is proposed in this paper. The element separates the deformable body from the rigid body in the formation. For the deformable body in the local coordinate system, the material nonlinearity is considered, and then the rigid body displacement is added. To consider the geometric nonlinearity in the transition from the local coordinate system to the global coordinate system, the co-rotational procedure is used. The formation principle of two-dimensional elements and the nonlinear solving process are given in the context. The example results show that the force interpolation fiber element based on the co-rotational procedure can accurately simulate the progressive collapse of RC frame structures. In the stage of beam mechanism, the material nonlinearity plays the key role, while whereas in the stage of catenary mechanism, the geometric nonlinear plays the key role.