The influence of structural retrofitting on the seismic behaviour of unreinforced masonry buildings

The research work investigated the influence of structural retrofitting on the seismic behaviour of unreinforced masonry (URM) buildings. The effect of various types of retrofitting was studied on the seismic behaviour of the masonry structures. The relevant seismic design codes do not clearly recommend the pertinent structural coefficients in the case of retrofitted masonry walls and buildings. The current study also identified and addressed the mentioned gap for the retrofitted masonry construction. The nonlinear micro simulation of the previously tested wall specimens was conducted using ABAQUS to verify the walls behaviour and the corresponding failure modes. The performance of URM and retrofitted buildings were assessed through the validated finite element models of wall specimens developed using the geometrical and material properties of the previous experimental study, which allowed implications to be made regarding the recommended seismic and structural factors. The parametric study of hypothetical one-storey and three-storey URM buildings using the characteristics of the tested wall specimens were performed. The studied parameters were the stiffness of floor diaphragms, the pier and spandrel aspect ratios, different types of openings and the pushover loading directions. Nonlinear static analysis was used to study the effect of each parameter on the performance of the models. Four methods of bilinear idealisation were introduced and employed to calculate the structural ductility factor and structural performance factor. Finally, a case study heritage masonry building was selected. The seismic performance of the building in both its original and retrofitted forms were investigated. The case study, Frederick Ash building, is located in Newcastle, Australia. The original (constructed in 1855) and the current retrofitted forms of the structure were considered. Linear static analysis, modal response analysis, nonlinear static analysis and nonlinear time history analysis were performed and reported on the mentioned four-storey building. The effects of retrofitting and changing the diaphragm flexibility of the structure on its seismic behaviour were investigated. The aim of the study was not only to investigate the failure modes and the displacement contours of the tested walls but also to extrapolate the assessment of the masonry walls to a bigger scale of unreinforced and retrofitted masonry buildings as well as investigate the effect of retrofitting on their ductility and performance. The ultimate aim was to suggest implications for seismic codes and standards regarding the structural factors of unreinforced and retrofitted masonry walls and buildings.