Issues on the use of time-history analysis for the design and assessment of masonry structures

Abstract

Nonlinear dynamic analysis is widely recognized as the most accurate analysis technique for the design and assessment of structures. However, its use is still not common in the everyday engineering practice, mainly due to various issues concerning its performance and the interpretation of its results. A first issue includes the limited availability of computer programs that allow the performance of time history analysis, especially for the case of masonry structures, although some software are currently available to this aim. Another difficulty is related with the selection of appropriate input ground motion records to be used for the analysis. Real records are well known to be a preferable choice with respect to artificial or synthetic ground motions, but the limited availability of real records often requires scaling them, with all the concerns associated with this operation. Also, a proper selection of seismic input requires some level of expertise, which is not so common in the professional field. A third problem regards the difficulty in the interpretation of the results of nonlinear dynamic analysis in terms of performance limits. The definition of significant limit states in relation to the results of nonlinear dynamic analyses is still indeed a very open problem and it is related to the fact that the achievement of a local limit condition (e.g. failure of a pier element) would not adequately represent the overall damage state of the building. Therefore there is the need to find a definition of limit states describing the global building performance, i.e. taking into account not only the peak concentrated damage in a single element, but also the diffusion of damage through the different structural elements and the evolution of the global collapse mechanism. This would also allow for a rational implementation of the qualitative definition of damage states commonly adopted in performance-based earthquake engineering.