Realistic seismic assessment of RC buildings with masonry infills using 3D high-fidelity simulations

This paper presents a high fidelity nonlinear modelling strategy for accurate response predictions of reinforced concrete (RC) framed buildings subjected to earthquakes. The proposed numerical approach is employed to investigate the seismic performance of a 10-storey building, which is representative of many existing RC structures designed with no consideration of earthquake loading by following design strategies typically used in Italy before the introduction of the first seismic regulations. The seismic response of the representative building is investigated through detailed nonlinear dynamic simulations using ADAPTIC, an advanced finite element code for nonlinear analysis of structures under extreme loading. The analysed structure is described by 3D models, where beam-column and shell elements, both allowing for geometric and material nonlinearity, are employed to represent RC beams, columns and floor slabs respectively. Furthermore, in order to model the influence of non-structural components interacting with the main frame elements, masonry infill panels are described using a novel 2D discrete macro-element representation, which has been purposely developed within a FE framework and implemented in ADAPTIC. The nonlinear dynamic simulations are performed considering sets of natural accelerograms acting simultaneously along the two main horizontal and the vertical directions and compatible with the design spectrum for the Near Collapse Limit State (NCLS). To improve computational efficiency, which is critical when investigating the nonlinear dynamic response of large structures, a partitioning approach, previously developed at Imperial College, has been adopted. The numerical results, obtained from the accurate 3D nonlinear dynamic simulations, have shown an extremely poor seismic performance of the building, for which collapse is predicted for seismic events characterized by lower magnitude compared to the expected more catastrophic earthquake. The comparison of the results obtained for the bare frame building or allowing for non-structural infills contribution shows significant variation in the dynamic responses. This confirms the need to consider the influence of masonry infill panels for a realistic description of existing RC building structures not designed to resist earthquakes.