Out-of-Plane fragility of In-Plane damaged unreinforced masonry infills in low rise reinforced concrete buildings

Unreinforced masonry (URM) is commonly used to make infill walls in reinforced concrete (RC) frame buildings. Such infill walls are highly vulnerable to out-of-plane (OOP) seismic loading and this can result in huge economic losses and human casualties. Therefore, fragility assessment of URM infill walls under seismic loads is important in view of performing large-scale risk analysis. In this paper, OOP fragility functions are provided based on a numerical investigation supported by a macro-element model. The fragility is calculated assuming the uncertainty in the geometric and mechanical properties of infills instead of the variability in the seismic input. Further, the effect of in-plane (IP) and out-of-plane (OOP) interaction is taken into account. Finally, the sensitivity of the results to the infill position in low rise buildings is discussed. Experimental data available in the literature are used for the validation of the output. Overall, the results indicated lower vulnerability in the OOP direction for infill walls without IP damage and high vulnerability in the OOP direction in the presence of previous IP damage. The vulnerability was found also increasingly proportional to the positioning of the panels at higher floors where the spectral acceleration of the structure is higher too. The proposed procedure can be extended to other types of infill walls depending on the construction technique of the site of interest, obtaining different and specific fragility curves for large-scale risk analysis.