Structural reliability analysis of unreinforced masonry party walls subjected to lateral earth pressure acting at the lower courses

Abstract

The Maltese Islands have a high population density of circa 1,380 people per sq.km, leading to buildings being constructed adjacent to each other with shared or unshared party walls. Party walls are walls setting the property boundaries and shared party walls are co-owned and loaded by the buildings owned both neighbouring parties. Their building material is typically unreinforced masonry (either Globigerina limestone or hollow concrete blockwork) due to the local availability of masonry blocks, their low building cost and the satisfactory compressive strength exhibited by the masonry units, making masonry one of the most popular building construction materials. The primary concern of these masonry party walls is their limited lateral resistance, specifically when these multi-storey walls are exposed to lateral loading. Sometimes, this situation is created by unbalanced lateral earth pressure at the bottom courses of such walls, as a result of excavation taking place on one side only. This situation has recently led to a number of building collapses locally, calling for more technical knowledge and investigation in this regard. This research study builds upon existing research on the determination of earth lateral pressures acting at the lower level of these party walls. Level 2 FORM (First Order Reliability Method) and SORM (Second Order Reliability Method) Structural Reliability Analyses were carried out to understand the uncertainties associated with the available structural design methods and to find the probability of these masonry walls losing their structural integrity as well as the major contributing variables affecting structural behaviour. The results from this parametric study were compared to Level 1 design code results and recommendations were outlined, based on the results obtained. This dissertation concluded that the dominant mode of failure for masonry walls is the out of plane failure mode, for which level 2 analysis gave a more realistic outlook of the probability of failure. This is true especially in the case of cohesive fills, where level 1 deterministic analysis using partial safety factors gave a false sense of security, which was eliminated by comparison to level 2 results.