Seismic performance of typical hybrid buildings in the urban centre of Barcelona

Abstract

Unreinforced existing masonry buildings, located in many historical urban centres, present specific construction characteristics that can have a significant impact on their seismic performance. As these structures are often designed considering only gravity loads before the introduction of seismic codes, they are commonly found to be particularly vulnerable to seismic actions. This work investigates the seismic performance of representative existing masonry buildings located in the Eixample district of Barcelona, Spain. These buildings are characterised by several common structural features, allowing grouping them into building typologies characterised by a similar structural response. The results of a building taxonomy of the specific district manifest the existence of two structural typologies related with the load-bearing system: one with load-bearing slender masonry walls throughout the whole height and a second hybrid one with steel beams and cast-iron columns on the ground floor and unreinforced masonry walls in the upper ones. The second typology is very common because it allows for large open space at the ground floor level, commonly used for commercial or administrative facilities. The drawback of this hybrid structural system is its reduced seismic performance, as the slender piers at the ground floor facilitate the development of a soft-storey mechanism. The main objective of this paper is to evaluate the seismic vulnerability of a typical hybrid building system composed by steel frames on the ground floor and unreinforced masonry at the upper floors. The seismic assessment and the identification of the collapse mechanism of this building typology have been carried out using the Finite Element Method. Seismic loading has been simulated through non-linear static (pushover) analyses in two main directions (parallel and perpendicular to the façades). The results of the numerical analysis allow a better understanding of the seismic performance of hybrid steel-masonry building typologies. This work is part of an ongoing research devoted to a large-scale seismic vulnerability assessment of the most representative building typologies of the Eixample district.