Analytical Procedure for Seismic Assessment of Masonry Buildings With Historical Value

Abstract eng:
Today, about 60 years after the proliferation of reinforced concrete in urban construction, structures that are classified as heritage buildings carrying a significant value from the past belong mostly to the class of unreinforced load-bearing masonry construction (URM), dating back to the 19th and early 20th Century. Extending current practices for seismic assessment to these buildings is not straightforward, as, in contrast with conventional frame structures, they are characterised by distributed stiffness and mass and poor diaphragm action. Interventions are often restricted by international treaties for non-invasiveness and reversibility of the intervention - given the practical requirements for the buildings’ intended reuse. Poor understanding of the mechanics of masonry and the inherent brittleness of the material further compounds the uncertainties in analytical methods used for assessment and rehabilitation. Simplified procedures that produce dependable results for estimating seismic demand for this class of structures are a primary objective of this paper. In a displacementbased context, requirements are determined from the spectral acceleration and displacement at the end of the constant acceleration range, Tc, in light of the fact that these structures seldom exceed two storeys in height above ground. Displacement demand at the reference point is then distributed through the structure following a simplified estimate of the fundamental mode of vibration; this is calculated in each of the two principal directions of the building in plan, by applying a lateral load distribution analogous to its mass distribution. The intensity of local demand and likelihood of damage are estimated as relative drift ratios, in plan and in height, of the masonry piers of the structure. A case study of two neoclassical buildings damaged in the 1978 earthquake in Thessaloniki are used as a point of reference for illustration of concepts - results are correlated based on their ability to reproduce the patterns of damage observed during post-earthquake reconnaissance evaluations of the building.

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