Seismic Performance Evaluation of Timber-framed Masonry Walls. Experimental Tests and Numerical Modelling

The Borbone constructive system used in Calabria at the end of the 1700s consisted of a particular composite structure realized by means of a timber frame suitably embedded inside masonry walls. This system used with similar purposes, although in different ways, in other places in the world (especially in seismic regions), can represent, with good reason, the synthesis of scientific knowledge in eighteenth century seismic engineering. The aim of the paper is to investigate and evaluate the seismic performance of the structure described above through a comparison between experimental tests, carried out by means of cyclic tests on 1:1 scale models, and the results obtained by the numerical modeling of the mechanical system that is capable of interpreting the actual contribution of the wooden structure, as well as that of the masonry, to the overall stiffness of the wall. In the numerical procedure, the masonry infill is modeled by rigid blocks connected by unilateral elastic contact constraints. A convenient way to define the contact device which links the blocks, through which a mortar joint or dry joint could be simulated, is to consider a set of elastic links, orthogonal to the contact surface between two adjacent blocks, and an additional link, parallel to the interface through which the shear forces can be transmitted. Reasonable hypotheses can be assumed for the link parallel to the contact surface in order to calibrate both the shear behaviour and the influence of the friction between the blocks. Furthermore the timber frame is modeled by using finite elements with elastic and bilateral behaviour. Unilateral contact constraints are again used in the contact interfaces between elements in wood and masonry blocks which take into account the actual contribution of friction. The mechanical parameters used in the numerical model were deduced from the experimental laboratory tests.