Seismic Vulnerability of Borbone Masonry Reinforced with Timber Frames

Abstract

After the 1783 earthquake, under the Borbone kingdom, new building regulations were introduced in the Calabria region (Italy) with the main scope of reducing the seismic vulnerability of the building asset in these highly seismic areas. The Borbone system consisted of masonry walls reinforced with timber frames and prescribed a symmetrical development in plan and elevation as well as height limitations. These measures aimed at increasing the seismic resistance of buildings and hence, in general, at reducing the socio-economic impact of future seismic events. In order to maintain, repair or retrofit these buildings, it is indispensable not only to understand their qualitative performance under an earthquake loading, but also to gain quantitative information on stiffness, load bearing and energy dissipation capacity and failure modes. This paper presents first investigations on the seismic vulnerability of simple Borbone structures where modelling assumptions such regularity in plan and elevation hold and only one shear wall system was used. Re-built shear wall specimens mirroring as exactly as possible a wall of the Palazzo Vescovile in Mileto (Italy), built according to the Borbone Istruzioni after the 1783 earthquake, were tested under quasi-static cyclic in-plane loading. By means of these tests, lateral properties and damage patterns of Borbone shear walls under horizontal loading were assessed and, even if limited to a single panel, earthquake behaviour patterns were evaluated. The test results on the shear walls in terms of hysteretic loops were used to develop a non-linear dynamic lumped mass model of a case study Borbone building which was subjected to various earthquake accelerograms. The single earthquake’s peak ground acceleration (PGA) values were increased until a previously defined near-collapse state in terms of maximum interstorey drift of the modelled building was reached. The thus obtained ultimate values for the PGA represent the sustainable level of seismic action of the investigated Borbone structure and ranged from 0.25g (North American earthquake) up to 1.52g. The effectivity of Borbone building regulations could be shown.