Modelling and nonlinear static analysis of reinforced concrete framed buildings irregular in plan

• Computer code for the nonlinear static analysis of r.c. framed buildings.
• Lumped plasticity model (LPM) to describe the inelastic behaviour of a r.c. frame member.
• Flat surface model (FSM) to describe the axial load–biaxial bending moment elastic domain of a r.c. cross-section.
• Capacity domains of a r.c. building with an L-shaped plan, to identify the in-plan seismic vulnerability directions.

Reinforced concrete (r.c.) existing structures with asymmetric plan may require the assessment of the seismic vulnerability directions in terms of displacement and strength. To this end, a computer code for the nonlinear static analysis of spatial framed structures is developed, adopting a path-following analysis based on the arc-length method to obtain the pushover curve for an assigned in-plan direction of the seismic loads. The seismic response of the r.c. frame members is simulated with a simplified lumped plasticity model, which includes a flat surface model of the bounding surface of the axial load–biaxial bending moment elastic domain, at the end sections of girders and columns where inelastic deformations generally occur. A case study of the existing town hall of Spilinga, a small town near Vibo Valentia (Italy), is investigated. The building, a two-storey r.c. structure with an L-shaped plan, was built at the beginning of 1960; in 2004, the Administration of Spilinga carried out a survey of the structure and its materials. To improve the knowledge level of the Spilinga building the present work uses, preliminarily, a simulated design with reference to the codes in force at the time of construction. Then, comparisons with a refined fibre model are made in order to: (a) verify the reliability of the flat surface model approximating the elastic domain of r.c. cross-sections; (b) calibrate the lumped plasticity model by means of nonlinear static analysis of the test structure. Finally, capacity domains in terms of top displacement and base shear are proposed, which allow an estimation of the in-plan directions of least seismic capacity at the serviceability (i.e. operational and immediate occupancy) and ultimate (i.e. life-safety and collapse prevention) limit states imposed by the Italian and European seismic codes.