Damage assessment of unreinforced masonry buildings incorporating damage accumulation

Recent earthquakes have shown susceptibility of unreinforced masonry (URM) buildings to damage accumulation in seismic sequences or long duration ground motions. Current structural modelling approaches commonly disregard the damage accumulation in URM buildings or they are unable to accurately capture this phenomenon unless sophisticated FEM models are employed. Such models are not feasible in risk-based applications given the required large number of dynamic analyses needed to develop robust fragility and vulnerability curves. On the other hand, the common displacement-based engineering demand parameters (EDP), such as inter-story drift ratio, fail to capture the impact of damage accumulation in simpler, more manageable models. An alternative is to use advanced damage indices that are capable of monitoring the monotonic accumulation of damages. This study proposes a displacement- and energy-based damage index that uses, as the basis, the Park and Ang damage index, modified and calibrated through experimental data of individual URM elements. Our calibration procedure maps the physical observed damage states to the hysteretic response of the elements. Consequently, damage on the individual elements is aggregated to define a global damage state at building level. Validation is carried out based on an equivalent frame model of a building tested on a shake table. Additionally, the model is subjected to multiple ground motions of seismic sequences and to long-duration ground motions to evaluate the performance of the proposed damage index. In comparison with displacement-based damage measures, the proposed damage index shows a superior ability to capture cumulative damage, even when simplified models are employed.