Keywords: masonry, historical building, seismic analysis, wooden structure, discrete block.

The paper addresses the problem of modelling the behaviour of historical masonry structures under seismic actions, with particular emphasis on the influence of the internal wooden structures. The building analyzed is a structure typical of the historical centre of Lisbon. This characteristic type of construction employed thick masonry walls, coupled to an internal wooden structure. Previous studies have stressed the good seismic features of this type of construction [1].

A discrete block model of a four-storey building is employed for time domain non-linear analysis. 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. In a previous study [2], this type of model was applied to a similar building, and a comparison of various types of internal wooden structures and pavement options was analyzed. The assumption of an elastic connection between pavement and external walls was then made.

In the present study, the wooden pavement beams are modelled using structural elements, which are linked to the masonry walls by connections with non-linear behaviour. The beam-wall connection may slide and fail, allowing an estimation of the influence of these construction details on seismic behaviour.

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 blocks 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. Several values of strength of the beam-wall connections were considered, which led to different types of behaviour, ranging from a response close to the elastic connection model, to another approaching the model with only external walls.

The study presented shows that discrete block models are an interesting tool for the seismic analysis of historical masonry buildings, as they are capable of simulating advanced stages of structural deformation and failure. Internal wooden structures may be easily included in the analysis, so that the influence of their stiffness and strength on the structural response and the safety may be evaluated.

The numerical results show that the effect of traditional wood pavements on the seismic behaviour is very much dependent on the soundness of the connections between them and the masonry walls. Failure of connections or sliding of beam supports renders them rapidly ineffective. Therefore, numerical models need to be capable of simulating this type of non-linear behaviour, as the common assumption of an elastic link is obviously unsafe.

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

A.J. Morais, J.V. Lemos, "Seismic Analysis of a Historical Masonry Building", in Proceedings of the Eleventh International Conference on Civil, Structural and Environmental Engineering Computing, B.H.V. Topping, (Editor), Civil-Comp Press, Stirlingshire, United Kingdom, paper 224, 2007. doi:10.4203/ccp.86.224

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