Dependence of the dynamic coefficient on rigidity of trusses in case of versatile local failures

Abstract

Introduction. To ensure the safety of buildings and structures in case of emergency, structures and individual structural elements must maintain their bearing capacity in the event of local damage. The purpose of the article is to study the effect of rigidity of a steel truss on the dynamic coefficient in the process of analyzing resistance to progressive collapse. A solution to this problem is a stage in the development of a practical method for analyzing steel trusses in cases of local failures of elements. Materials and methods. Within the framework of the study, several numerical and analytical computations of steel trusses, having spans of 24, 48, 72, 108 and 144 m, were performed. Steel trusses were subjected to different local failures of elements in top and bottom chords. Results. The effect of rigidity of trusses on the dynamic coefficient is studied for cases of withdrawal of individual elements from the analytical model. Values of dynamic coefficients, obtained by means of analytical and numerical calculations, demonstrated good convergence (the discrepancy did not exceed 15 %). The dynamic numerical calculation of the 3D roofing skeleton with a standard pattern of horizontal ties was performed, taking into account the local failure of a truss element. The distribution of the dynamic coefficient within a damaged truss and the nearest trusses was obtained. Conclusions. Analytical and numerical studies showed that an increase in the rigidity of a truss caused a reduction in the value of the dynamic coefficient. Analytical dependences can be used as the bearing capacity reserve when making analytical calculations. Numerical analysis showed that if a damaged truss resisted loading, being part of the 3D framework of an industrial building, the load, acting on the damaged truss, was redistributed to neighboring trusses, and dynamic forces in it were smaller than those in an independent load-bearing truss. The damage of the compressed chord was a worse case; the value of the dynamic coefficients exceeded the values for the case of stretched chords by an average of 26 %, and the truss resisted loads nearly independently from neighboring trusses, behaving as a flat element.