Towards the Development of a Seismic Assessment Code for Urm Structures

Abstract eng:
Load-bearing unreinforced masonry (URM) structures present several special characteristics that set them apart from common engineered construction, such as weak diaphragm action, spatial distribution of mass (massive load-bearing walls), and inherent brittleness and negligible tensile strength. For this type of structures, a complete methodology is developed intended to enable seismic protection through assessment and retrofit particularly aimed at historical and heritage structures. The methodology includes the attributes of a performance-based prenormative framework, including systematic procedures for setting assessment response indices and acceptance criteria based on deformation demand and supply measures. The required methods of analysis and allowable simplifications and confidence limits are detailed, along with acceptable interventions that are compatible with the material physical characteristics and retrofit conventions when the URM structure also carries some cultural significance as is frequent the case. The proposal presented concerns prenormative provisions for management of the seismic risk posed by URM structures, including illustration of methods and handling of uncertainty in all steps of the process. Performance of URM structures in past earthquakes that motivate the need for better understanding certain response aspects, particularly out of plane rocking and ways to limit that through timber lacing and other methods are discussed in order to highlight the vulnerabilities of this class of structures in severe seismic events and quick ways to eliminate critical pathologies against out-of-plane action.

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