Analytical model for progressive collapse of RC frame structures subjected to blast loadings

Abstract

An improved analytical model that enables tracing of the progressive collapse of RC frame structures under blast loading is introduced in this paper. The moment-curvature relation uniquely defined in an RC section is used for the simulation of the bending behavior, and then the constructed nonlinear moment-curvature relation is modified with the consideration of many factors such as the effects of bond-slip, axial force and catenary action, which dominantly affect the nonlinear response of RC structures. Upon the definition of the monotonic moment-curvature envelope, the hysteretic unloading and reloading paths are defined to trace the dynamic bending behavior of an RC section on the basis of the hysteretic curve of reinforcing steel. In advance, to describe the direct shear failure, the empirical direct shear stress-slip relation suggested by Krauthammer and Astarlioglu is considered in the solution procedure and implemented into the formulation with the use of non-dimensional spring element. Moreover, as was in the moment-curvature relation, the hysteretic rule in the shear stress-slip relation proposed by Krauthammer and being used in many previous researches is also adopted. Because the numerical approach based on the moment-curvature relation of RC sections will dramatically reduce the solution steps, this approach makes it possible to trace the collapse not only of RC members but also of RC structures that are comprised of many structural members and require enormous solution procedures. After verifying the reliability and accuracy of the introduced numerical model through correlation studies of the RC members and a simple frame, the collapse analyses of multi-bay and multi-story RC frames are performed to prove the possibility for the progressive collapse analysis of entire frame structures only with the use of beam elements.