GNGTS 2019 - Atti del 38° Convegno Nazionale

440 GNGTS 2019 S essione 2.2 Non-linear static and dynamic analyses. The first step for the seismic assessment is obtaining a proper model of the investigated structure. However, these buildings are complex geometry, which requires simplifications in order to obtain FE model able to reproduce the structural behavior realistically. In order to reduce the computational burden and obtain a convergent behavior of the solution in all ABAQUS simulations, a sensitivity analysis to set the correct mesh seed is also performed. In the latter, the mesh size is related to the natural frequencies and the participating mass for the three main modes. Moving on, the nonlinear Pushover Analysis (PA), according to the N2 method adopted by Structural Codes (Circolare, 2009, NTC, 2018), is carried out. Through this method, the seismic vulnerability is evaluated by the conversion of the multi-degree of freedom system (MDOF) into the equivalent system with a single degree of freedom (SDOF) by using the modal participation factor. The PA consists in applying the vertical action including gravity loads and then in considering the seismic forces, acting separately along the positive and negative geometric directions (X and Y) of the analyzed structure (Clementi et al. , 2016). In the simulations, a mass-proportional force distribution pattern is assumed, corresponding to a uniform horizontal acceleration pattern. As a matter of fact, the triangular shape of the building suggests to considerer three Boundary Control Points (BCPs) onto the three vertexes. Their selection plays a very important role in the evaluation of the seismic vulnerability because the three nodes, namely C1, C2, and C3, show different displacement values at the collapse time. In Fig. 1, the results of +Y PA are reported. In Table 1, the results of PAs are reported in terms of safety factors F S (ratio between displacement capacity d * C and seismic demand d * D of the SDOF system), behavior factor q * (ratio between the elastic forces and the yield ones of the SDOF system, which represents the ductility of the structure) and spectral acceleration (ratio between shear force F * and participating mass m * ) for the three BCPs. Subsequently, the validation of PA results has been performed by using the Response History Analysis (RHA) based on the application of an artificial accelerogram along the X or Y directions. In these analyses, the same model used in PAs is now subject to gravity loads, in the first phase, and, in the second phase, to an accelerogram applied to the base separately for each direction. With the aid of RHAs, the time histories of base shear, damage variables, and displacements of the control points might be assessed (Fortunato et al. , 2017). Fig. 2 shows the results of RHA in Y direction. Fig. 1 - Results of PA for +Y direction and BCPs localization.