Damage-free self-centring links for eccentrically braced frames: development and numerical study

Many recent research studies focused on the development of innovative seismic-resilient structures, chasing the objectives of minimising both seismic damage and repair time, hence allowing the definition of structures able to go back to the undamaged, fully functional condition in a short time. Steel seismic-resilient structures have been widely investigated in the past few years while considering solutions based on moment-resisting and concentrically braced frames. While the first category may be characterised by low stiffness, the second category is often characterised by low ductility. Conversely, eccentrically braced frames (EBFs) represent a compromise between the two and allow both strength and stiffness to be optimised while providing 'good' ductility capacity. The present study investigates a solution for damage-free self-centring EBFs relying on damage-free self-centring devices as seismic links (SC-links). The SC-links are based on post-tensioned high-strength steel bars with disk springs to provide the self-centring behaviour, and friction dampers to dissipate the seismic energy. Analytical equations governing the global behaviour of the connection are developed. A four-storey EBF complying with Eurocode 8 provisions is designed with conventional seismic links and upgraded with the proposed SC-link. The third storey of the structure is extracted to develop refined 3-D finite element (FE) models in ABAQUS. The results of the FE simulations are used to investigate the local behaviour of the seismic device and validate the accuracy of the analytical predictions. Moreover, a simplified 2-D FE model is developed in OpenSees to carry out Incremental Dynamic Analysis providing information on the global response of the structure. Residual and peak interstorey drifts and link rotations are monitored as Engineering Demand Parameters, and the seismic performances of the frames are compared.