Investigation of bolted joint behaviour in dynamic progressive collapse analysis of steel frames

Abstract

This research focuses on developing an efficient numerical model for dynamic analysis of steel framed structures subjected to sudden column removal scenario in order to assess the potential resistance of progressive collapse of the structures. As a basis of the whole research work, a finite element structural dynamic analysis program was developed based on Bernoulli-Euler beam theory and 2D co-rotational finite element formulation. Both material and geometric nonlinearities were considered. A comprehensive verification study of the finite element program was performed against analytical and numerical results of some well-established benchmark tests. Since the structural joints are the primary components to resist progressive collapse when extreme loads occur, it is important to model the joint behaviour accurately in the dynamic progressive collapse analysis. To achieve this aim, three series of tests were conducted to investigate the dynamic behaviour of some of the commonly used steel beam-column joints (including web cleat, flush end plate and top and seat with web angle joints) under sudden column removal scenario. In addition, detailed 3D finite element simulations were carried out to investigate the dynamic behaviour of the steel joints under such scenario. The Dynamic Increase Factors (DIFs) were also investigated. The test and simulation results showed that both the force-based DIF and displacement based DIF were dependent on the type of joint. For web cleat and top and seat with web angle joints, the values of the force-based DIF could be greater than 2.0. Finally, component-based steel beam-column joint models were proposed to model the dynamic behaviour of the three types of joints. The models were implemented as an assembly of defined joint elements in the developed finite element program. Parametric studies on different layout of steel framed structures were carried out to investigate their dynamic performances to progressive collapse. From the cases studies, it was shown that the resistances of steel frames were significantly affected by the axial restrains of the undamaged structural members adjacent to the damaged column. The resistances of unbraced frames may decrease with the increase of the storeys.