The seismic resistance of unreinforced masonry (URM) building aggregates of high building unit plan slenderness with soft storey basements on rock subsoil

Abstract

This research study aims to investigate the seismic behaviour of URM building aggregates on Ground Type A (rock) subsoil, built with local Globigerina Limestone and class M2 mortar. The research aims to provide the maximum number of floors that a specific building aggregate typology can withstand when subjected to the design peak ground acceleration (PGA) applicable to the Maltese Islands. Furthermore, basic concepts related to earthquake engineering, especially on rock subsoil, and the seismic responses of URM building aggregates are outlined throughout the study. The methodology adopted in this study is a non-linear static pushover analysis. The 3D Macro numerical seismical analysis software is used to simulate the seismic performance of URM building aggregates and, through a computational process, the results obtained are presented in a series of graphs according to the type of pushover analysis carried out. Such representation of results allows direct comparison between various building aggregates and also the performance of a specific aggregate configuration with a different number of floors (seismic levels). Furthermore, three building aggregates were tested on Ground Type B (very stiff clay) and Ground Type C (stiff clay) subsoil to determine the variation of the seismic performance of the building aggregates for different geological ground conditions. Following the completion of the afore-mentioned seismic vulnerability assessments, it has been demonstrated that the peak seismic resistance of URM building aggregates on Ground Type A subsoil, is obtained for three individual building units within a building aggregate configuration. On the other hand, the capacity of the number of possible floors that can be safely carried by the building aggregate within an earthquake event is largely unaffected by the increase in the size of building aggregates consisting of four or more individual building units. While this research study focused on building aggregates, which were roughly square on plan, the study also highlighted the need to investigate other building aggregate plan configurations in order to determine whether the conclusion derived from this dissertation are also applicable to other non-square building aggregate configurations.