Seismic Assessment of a Complex Timber-Masonry Structure: Ica Cathedral (Peru)

Abstract eng:
This paper discusses the structural performance and addresses the seismic assessment of Ica Cathedral, which is one of the four buildings involved in the ongoing Getty Seismic Retrofitting Project, under the auspices of the Getty Conservation Institute (GCI). The aim of this work is the evaluation of the dominant mode shapes of the structure as predicted by the model, and also the comparison with the dynamic identification performed during the on-site visit conducted during MayJune 2015, by a team from the University of Minho, the reproduction of the existing structural damage using advanced numerical analysis and the safety assessment of the structure in its current condition. These tasks are challenging due to the complexity of this historical building and to the numerous unknowns on the morphology and material properties. In fact, the Cathedral is composed by two sub-structures: an external (mostly) earth envelope and an inner timber frame. The characteristics of the timber substructure have shaped the adopted procedure for its analysis. This substructure is composed by a vast number of main elements usually connected by some additional bracing elements. Another factor adding complexity to the model is the definition of the connections between the elements. This is one of the most challenging aspect to be evaluated in historical timber structures as the characteristics of the joints depends on the region, period of time and carpenters’ know-how. For all these reasons, initially, just a single representative bay has been studied. Analysis under vertical loading and parametric analysis under mass proportional lateral loading have been performed using the SAP 2000 software. The structural analysis of the masonry envelope involving a finite element representation is based on geometric and inspection surveys performed. Nonlinear static under gravity loading, eigenvalue, pushover and time history analyses will be addressed. The analysis adopted a macro-modeling approach of the adobe structural parts and base course stone foundation, with a total rotating strain crack model, allowing to consider specified compressive and tensile softening behaviour, based on fracture energy concepts. Finally, the analysis of the entire structure of Ica Cathedral will be presented, with appropriate considerations on the connection between the two sub-structures. While keeping valid the considerations made on the masonry envelope and timber frame, the structure will be studied in terms of nonlinear static under gravity loading, eigenvalue, pushover and time history analyses.

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