Behavior factor estimation for seismic design of unreinforced masonry buildings

The use of new geo-sourced construction materials in seismic areas requires the assessment of the structure ductility in order to properly design the building. This research aims to propose a procedure for behavior factor estimation in case of using a new construction material. In particular, in this paper, the proposed methodology is applied to an unreinforced masonry building in an average-risk seismic zone. Before application for seismic design, the reliability of the selected equivalent frame modeling approach is validated by comparison of dynamic features obtained from both numerical and operational modal analysis. An existing stone masonry building is selected as case study to validate the modeling approach. A measurement campaign provides the structural response to ambient vibrations and structural damping. After validating the model in elastic conditions, the building ductility capacity is estimated using a numerical pushover analysis, for different load combinations and distributions, according to the European design code, under the assumption of perfect plasticity. The proposed procedure provides a behavior factor obtained specifically for the analyzed building, using a relationship between ductility demand and behavior factor deduced from dynamic analysis. The average ductility demand is estimated numerically, for a set of synthetic acceleration signals compatible with the Eurocode elastic response spectrum and a given behavior factor. Finally, it is suggested to verify the near collapse limit state of the building structure not only in terms of target to capacity displacement ratio but also in terms of load ratio, since it can be more restrictive in some instances.