Aftershock fragility assessment of Italian cast-in-place RC industrial structures with precast vaults

Through a fragility analysis carried out with different probabilistic methods, the vulnerability of an Italian cast-in-place RC industrial structure with precast reinforced hollow brick light-weight vaults is evaluated via nonlinear analyses. After a brief description of the vault construction system, a typical case study built in the 1960s is considered and the influence of FE numerical modelling through three different representations of the vault system is assessed. Fragility curves are calculated by Incremental Dynamic Analysis (IDA), with three damage limit threshold values corresponding to local limit conditions regarding bending or shear that first occur in a few elements, as determined through pushover analyses. A comparison of fragility curves in the two horizontal directions (X-Y) for the three models is reported. Concerning the model with the greatest probability of collapse, seismic sequence effects on structural damage with the same ground motions for mainshock and aftershock are taken into account. Double Incremental Dynamic Analysis (D-IDA), with the mainshock represented by several fixed percentages of Near Collapse PGAs previously evaluated in X-Y directions and scaled aftershocks, is performed and compared to the IDA results. Aftershock fragility curves created with only the damage limit threshold value of Near Collapse are likened to the case that analyses a single seismic event (undamaged structure). Furthermore, ductility damage indices are calculated for maximum displacements obtained by each nonlinear dynamic analysis of IDA and D-IDA.