Self-Centering systems aim to eliminate or minimize residual drifts in structures leading to improved seismic performance and allowing immediate occupancy of structures during and post earthquakes, respectively. In this study a new compact Self-Centering Energy-Dissipative (SCED) brace is developed, designed, and experimentally tested. The new innovative compact high capacity ring spring SCED (RS-SCED) is a brace system that exhibits a nonlinear response with good energy dissipation and post-yield stiffness, while eliminating or minimizing residual drift after an earthquake.

Existing SCED braces typically rely on using prestressed tendons to achieve their self-centering capabilities. In conventional SCED braces, the tendon is required to be relatively long to achieve a large enough deformation capacity, resulting in SCED braces that are large in size. Similar SCED brace systems which do not rely on tendons to achieve their self-centering capability, tend to have a lower load capacity than conventional braces. Based on these constraints, the applicability of existing SCED braces is limited by size, as well as load and deformation capacity. The new high capacity compact ring spring SCED brace utilizes ring springs to provide a restoring force, while simultaneously dissipating energy through friction between ring spring units in the assembly. The new mechanism allows the brace to have a large deformation capacity without the need for a long tendon, resulting in a compact sized brace that can attain self centering behaviour during the earthquake response of a building for drift demands up to 4%, and potentially larger if necessary. The new RS-SCED brace has high load capacity with stable and repeatable hysteresis that makes them suitable for deployment in full scale building and bridge structures in high seismic regions.

Hybrid simulations are performed to evaluate the system level performance of the new brace in prototype structures. The hybrid simulation method allows for the realistic seismic assessment of critical structural components or subassemblies in a structure without the need to test the entire structure in a laboratory by combining experimental testing and numerical modelling together. In this study, a 4-storey building and a 3-span bridge with the new ring spring SCED brace are tested using hybrid simulations. The physical test substructure is the prototype compact high capacity ring spring SCED with a load capacity of 1400 kN and a deformation capacity of 160 mm. During the tests, the systems are subjected to a series of earthquake records with a wide range of frequency contents at different hazard levels.

In the new RS-SCED brace system, the seismic response of the structure can be improved through optimization of the brace design parameters, namely the brace pre- and post-activation stiffness, activation load, and deformation capacity. The optimization of these design parameters depends on the seismic demands on the structure, such as the storey drift and storey shear. Typical seismic design procedures rely on ductility and overstrength factors for simplified seismic analysis and design using an equivalent static force procedure. In this study, the FEMA P695 methodology is used to determine the ductility (𝑅), overstrength (𝛺0) and deflection amplification (𝐶𝑑) factors for seismic design of the proposed structural system. Two different levels of seismic hazard are examined for buildings with both short and long periods of vibration. To account for the variation in periods of vibration, the seismic responses of 2-, 4-, 8- and 12-storey steel framed buildings equipped with the new RS-SCED braces are examined. The combination of different building heights, bay sizes and seismicity levels led to the design of 12 different prototype building designs for the numerical analyses. Pushover analyses, as well as nonlinear dynamic time history analyses of the prototype buildings subjected to a suite of scaled ground motions are performed. The calibration of the seismic design factors for the RS-SCED braced frame buildings, is based on optimization of the seismic performance of buildings by considering the peak storey drifts, residual drift and floor accelerations.