Keywords: masonry, historical building, seismic analysis, numerical modelling, discrete block.

The paper addresses the problem of modelling the behaviour of historical masonry structures under seismic actions. A case study is presented of an eighteenth century building located in the downtown area of Lisbon which was rebuilt after the 1755 earthquake. This characteristic type of construction employed thick masonry walls, coupled to an internal wooden structure. Previous studies have pointed to some good seismic features provided by this type of structure [1].

The numerical modelling was based on a discrete block technique. These models are increasingly being applied to masonry structures, given their ability to represent their observed modes of collapse [2]. In this study, the simplest type of block model was used, which assumes that the blocks are rigid and all the non-linear behaviour is located at the joints, which are assigned the strength of the masonry material.

Discrete block models are primarily intended to analyze structural failure. However, to be of practical interest, they have to be capable of simulating correctly the complete structural response, including the early predominantly elastic range. Comparisons with elastic solutions have shown that rigid block models may provide an acceptable performance of the dynamic behaviour of pillars and walls in that range, namely the out-of-plane bending behaviour. Natural frequencies of the historical building were calculated, assuming elastic behaviour of joints, and they fall within the range of observed values for these structures.

A time domain dynamic analysis was performed, applying the regulatory seismic records for the region. The model with non-linear behaviour of the joints between the block was used, providing an assessment of damage, which is essentially reflected by the level of permanent displacements produced. The structure withstood the seismic action, but substantial damage is to be expected in the masonry walls. A trial run of a similar building with thinner walls ended in detachment and a fall of blocks. The influence of the internal wooden structure was also examined, showing that connection between opposite walls has a beneficial effect on the seismic performance.

The study presented shows the capabilities of discrete block models in the structural analysis of historical masonry buildings, namely for the simulation of the response to seismic actions. Advanced stages of deformation and failure processes may be approached by means of these techniques. Further developments are, however, still required for masonry analysis, particularly in the representation of the internal wooden structures and reinforcement techniques.

1

V. Cóias e Silva, P.B. Lourenço, L.F. Ramos, C.G. Mesquita, "Accounting for the 'block effect' in structural interventions in Lisbon's old 'Pombaline' downtown buildings", in "Historical Constructions", P.B. Lourenço, P. Roca (Eds.), Guimarães, 943-952, 2001.

2

J.V. Lemos, "Modeling of historical masonry with discrete elements", in III European Conf. on Computational Mechanics Solids, Structures and Coupled Problems in Engineering, Lisbon, Portugal, C.A. Mota Soares, J.A.C. Martins, H.C. Rodrigues, J.A.C. Ambrósio (Eds.), 375-392, 2006. doi:10.1007/1-4020-5370-3_23

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