A Multi-Objective Displacement-Based Design Procedure of Viscous and Hysteretic Damped Braces for the Seismic Protection of Rc Buildings

Abstract

The use of hysteretic damped braces (HYDBs) is an effective and low-cost solution for the seismic retrofitting of reinforced concrete (RC) framed structures. However, notable damage to nonstructural elements can be observed at the serviceability design earthquake (SDE), when too high activation forces of the HYDBs are designed in order to attain structural safety (SS) performance level at the basic (BDE) and/or maximum considered (MCE) earthquakes. On the other hand, HYDBs designed at the immediate occupancy (IO) performance level prevent nonstructural damage of MIs under SDE but may collapse and/or induce structural damage for high intensity seismic loads, due to their early activation which renders them unable to develop large energy dissipation. Aim of this work is the proposal of a multiobjective displacement-based design procedure, where viscous damped braces (VDBs) and HYDBs calculated for IO at the SDE are combined with HYDBs ensuring SS at the MCE. A six-storey RC framed structure, representative of the residential building stock in Italy prior to the 2008-2018 code changes, is to be retrofitted in a high risk-seismic region supposing that is preliminarily designed in L'Aquila (Italy) for moderate seismic loads. The OpenSEES platform is considered for the nonlinear dynamic analysis of the original and retrofitted structures. RC frame members are modelled with lumped plasticity elements while the shear behaviour of the beam-column joints is modelled by means of a scissor model. Masonry infills uniformly distributed in elevation are modelled with a simplified diagonal pin-jointed strut model taking into account the in-plane failure modes. HYDBs are modelled with truss elements characterized by a bilinear force-displacement law, without considering the flexibility of the supports, while nonlinear force-velocity law is considered for VDBs. Nonlinear dynamic analysis is carried out considering three stripes of real records, corresponding to the SDE, BDE and MCE seismic levels assumed in the current Italian code. COMPDYN 2021 8 th ECCOMAS Thematic Conference on Computational Methods in Structural Dynamics and Earthquake Engineering M. Papadrakakis, M. Fragiadakis (eds.