Strain rate dependent component based connection modelling for use in non-linear dynamic progressive collapse analysis

Abstract

This paper introduces the use of rate dependent springs to component-based joint models. This allows strain rate hardening as well as strain rate induced reductions in ductility to be included in component spring models for inclusion in non-linear dynamic analysis. Experimental tests of fin-plate connections are carried out under static and dynamic conditions with loading time as low as 32ms to failure. The joints were tested under the combined effects of tensile load and rotation in order to simulate the complex conditions experienced by joints during catenary action. The strain rate modifications to the component models of the joint were observed to be able to accurately model strain rate induced hardening, as well as reductions in failure rotation which occur in joints under dynamic conditions.The rate dependent component models were subsequently incorporated directly into sub-frame models to simulate catenary action developed due to the loss of support to a column. The individual failure criteria of the joint components provide for an accurate simulation of the progressive fracture of joints during collapse. The results are compared with the conventional approach in which joints are modelled using axial and rotational springs. The comparison reveals that, for the scenario investigated, the conventional method leads to a 20% overestimation of load capacity, due to the lack of inclusion of dynamic material property effects and moment capacity reductions resulting from prying action and catenary action axial forces. Thus the approach goes some way to developing a more realistic approximation of moment–tension–rotation response through to fracture of joints in whole frame progressive collapse computer simulations.