Seismic performance and fragility curves of historical residential buildings in Lisbon downtown affected by settlements

Abstract

The construction of underground structures in Lisbon’s downtown, alongside with the fluctuation of the ground water level, generates settlement-induced damages to old heritage Pombalino masonry buildings. Assessing the potential damage caused by soil settlements to masonry structures is essential for adequate evaluation of their seismic performance and the definition of retrofit solutions. The seismic assessment procedures need to take into account the settlement induced damage and the non-linear behaviour of the masonry materials. This paper seizes a rare opportunity to join, in the same analysis, real settlement profiles imposed to well-characterized historical building typology, known as Pombalino, with the evaluation of their seismic performance simulated with advanced numerical models. Lisbon’s downtown settlements were measured for seven years. From these settlement measures, two settlements’ profiles and two settlements’ rate were identified. This paper presents the results of a study developed on a representative Pombalino building where these settlement profiles were applied to assess their impact on the initial damage and on the seismic performance of the building. The expected level of damage for a given ground motion intensity was estimated through the employment of numerical modelling and nonlinear static analysis, which has shown that damages induced by settlements can reduce significantly the global seismic performance of the building. The level of damage of the building at a global level and local level was studied. For the latter, the damage on structural elements is defined by the mean of the drift parameter, while for the former, the damages levels are defined directly in the pushover curve. This study assessed quantitatively the effect of the differential settlement on the seismic performance of Pombalino buildings and their fragility curves. The results showed the seismic action intensity needed to reach the collapse of the structure is roughly half for longitudinal configuration with the curved profile and nearly 1/5 for transversal shape with the linear profile, when compared to the building without differential settlements.