A Strength Criterion for the Flexural Behaviour of Spandrels in Un-Reinforced Masonry Walls

Abstract eng:
With reference to the in-plane behaviour of masonry walls, it is possible to recognize basically two structural components: piers and spandrels. Piers are the main vertical resistant elements for both dead and seismic loads. Spandrels are usually classified as secondary elements: although hardly investigated at all in literature (unlike piers), they significantly affect the seismic capacity of the structure. Firstly, a considerable energy dissipation is related to their damage. Moreover, the coupling effectiveness associated with these elements significantly influences the boundary conditions of piers (i.e. fixed-fixed or cantilever) with remarkable repercussions on the global response of the structure. In the case of existing buildings, common practice (explained by the frequent lack of other tensile resistant elements coupled) is to neglect masonry spandrels in the model leading to a large number of historical buildings being assessed as “unsafe” according to current seismic codes. It is clearly evident that such a result is not plausible: the adopted hypothesis is too severe and masonry spandrels supply unknown resources to the structure. Thus reliable predictive models are needed. In the paper a resistance criterion finalized to interpretation of their flexural behaviour is proposed. It has basically been founded on the interlocking phenomena which can be originated at the interface between the end-sections of the spandrel and the contiguous masonry. A set of parametrical non linear analyses has been performed in order to validate the proposal. Finally some applications to complex masonry walls are presented in order to assess the effects on the global response.

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