The residual structural strength of steel moment-resisting frame buildings subjected to seismic loading

Abstract

This research study was aimed at investigating the difference in the structural strength of a steel frame building between the Significant Damage Requirement and the Near Collapse Requirement limit states as defined by Eurocode 8 and, therefore, the residual strength of a steel frame building subjected to seismic loading corresponding to the design earthquake for the Maltese Islands. The dissertation investigated the strength of a number of standard steel structures beyond severe damage up until the point of structural collapse of the building. Throughout the research study, a number of basic concepts relating to the determination of the design seismic forces and good seismic engineering practice were discussed. The concepts outlined took into consideration the ground type considered which, in this case, was assumed to be rock. The aim of the dissertation was to investigate the significance of the effect of building plan length to-building plan width aspect ratios and building vertical height-to-building plan width aspect ratios on the design of steel frame buildings subjected to seismic loading. In particular, this research study assessed how different building aspect ratios lead to a number of different seismic vulnerabilities, where the narrower a building is on plan the worse are the associated torsional effects, while the taller a building the more susceptible it becomes to overturning about its base foundation. The research methodology adopted in this dissertation made use of a non-linear static pushover analysis. Furthermore, proprietary numerical software based on the Finite Element Method (FEM) was used in order to simulate numerically the structural performance of steel frame buildings under seismic loading. The results obtained were then represented through a number of pushover curves. These pushover curves were then used to carry out a comparative analysis of the structural performance and residual strength of the various steel frame buildings analysed. The research study gave a clear picture regarding the seismic risk of steel frame buildings depending upon their heights and plan aspect ratios, showing which of these buildings are at greater risk of structural collapse due to seismic action. The results obtained show that low-to moderate height buildings exhibit gradual unloading in the post-ultimate strength regime with decreasing post-ultimate residual strength as the building height increases. On the other hand, taller buildings are characterised by steep unloading post-ultimate strength curves with very little post-ultimate residual strength. The dissertation also made a number of suggestions for future research work in this field of study.