Simulation of damage observed on buildings in aggregate after the 2016-2017 Central Italy earthquake accounting for site effects and soil-structure interaction

The paper investigates the influence of site effects and soil-structure interaction on the response of buildings in aggregate in the historical centre of Visso, located in an alluvial valley in the Central Italy. The town was severely stricken by the Central Italy 2016/2017 seismic sequence and the subsequent inspections allowed the reconnaissance of damage suffered by the case study at hand. A monitoring system installed just out of the historical centre recorded the ground motion at Visso during the seismic sequence. Based on these records, the bedrock motion was then calculated through their deconvolution along the well characterized soil profile below the record station. The resulting signals were applied as input motions in linear equivalent site response analyses (i) of the 1D soil stratigraphy below the buildings in aggregate and (ii) of the whole 2D valley. In both cases, the subsoil model was inferred from the data gathered during the seismic microzonation study of the Visso village. The amplification of ground motion resulting from the 1D site response analysis is higher than that predicted by the 2D analysis along the same vertical. The whole aggregate was modelled in the Tremuri software through the equivalent frame approach and specific modelling strategies were adopted to account for the interaction among adjacent structural units. The model base was either completely restrained, to simulate the fixed-base conditions as typically assumed in the structural analysis, or endowed with springs, to simulate the effect of the soil compliance to the structural motion. Non-linear dynamic analyses were then performed on the fixed and complaint base models under the free-field motion obtained from the 1D and 2D site response analyses. The resulting damage patterns were compared to that detected on site. The comparison is satisfying only when the motion obtained from 2D site response is adopted as input motion and slightly improved when the compliant base conditions are considered.