Seismic vulnerability assessment of the Inquisitor’s Palace at Vittoriosa in Malta

Abstract

The Inquisitor’s Palace is one of the few remaining heritage buildings of its kind within the Maltese Islands, the rest having been lost to time or the French Revolution. It is a monumental structure which has undergone several changes over the years and comprises a veritable anthology of building styles and construction techniques. The building fabric is a showcase of artistic and architectural masterpieces. One of the major threats to any structure is an earthquake event. Malta is located in a low-tomoderate seismic hazard zone. The strongest recorded earthquake on the Islands is that of 1693. With a magnitude of 7.4 on the Richter scale, it caused severe damage to buildings in Valletta, Gozo and the Three Cities. Records of past earthquakes, coupled with the active seismicity of the Sicily Channel, suggest that it would be irresponsible to ignore the potential hazard of future seismic events. Unreinforced masonry (URM) buildings, which are inherently suited for compressive forces, do not generally perform well under seismic (and, predominantly lateral) loads. Heritage buildings, which have inherited added characteristics of age, piecemeal alterations and lack of seismic engineering considerations in the building design, are inherently even more vulnerable to such seismic risks. This research study is intended to determine the present seismic vulnerability of the Inquisitor’s Palace at Vittoriosa. It starts with a research study that maps out the successive structural changes and accretions, effected on the building fabric over the past 490 years. The next step involves the construction of a numerical building model. Using the software ‘3D Macro’, a series of non-linear static (pushover) seismic analyses are carried out to obtain the capacity curves of the structure as it is today. The findings of this research study clearly indicate that, while there is no danger of significant damage to the building under a seismic scenario, some building elements would still suffer deformations, which would irreversibly damage the integrity and cultural value of its features, namely the Grand staircase designed by Romano Carapecchia and the multitude of frieze frescos spread over the building fabric. The study thus concludes that there is a need for retrofitting/strengthening measures to increase the sway stiffness of the building. Thereby safeguarding the integrity and heritage value of the Inquisitor’s Palace if subjected to an earthquake event.