Using the macro-element method to seismically assess complex URM buildings

Abstract

Existing unreinforced masonry (URM) buildings are often composed of traditional construction techniques, with poor connections between walls and diaphragms that results in poor performance when subjected to seismic actions. In these cases the application of the common equivalent static procedure is not applicable because it is not possible to assure “box like” behaviour of the structure. In such conditions the ultimate strength of the structure relies on the behaviour of the macroelements that compose the deformation mechanisms of the whole structure. These macroelements are a single or combination of structural elements of the structure which are bonded one to each other. Building damage that arose from the Canterbury earthquake sequence was taken as a reference to estimate the most commonly occurring collapse mechanisms found in New Zealand URM buildings in order to define the most appropriate macroelements. When the macro-elements and their connections are defined, the next step is to impose equilibrium conditions and find the collapse mechanism most likely to be formed, via determination of the activation threshold (alpha = a/g). The classification of a building into macroelements and collapse mechanisms allows the definition of analytical methods to assess the seismic vulnerability. In addition to definition of the assessment process, the reported case study serves as an example for professionals around New Zealand. The level of considered earthquake shaking is consistent with New Zealand loading standards and is described in terms of the elastic site hazard spectrum C(T).