Seismic resilience and performance design approach for concrete moment resisting frame buildings equipped with yielding restrained braces

Advanced structural dissipation devices can be classified into three major groups including passive, semi-active and active control energy dissipations. While all of these technologies play an important role in structural design, passive energy dissipation devices are the most common types of control systems which can be classified into six types including Metallic Dampers, Friction Dampers, Viscoelastic Dampers, Viscous Fluid Dampers, Tuned Mass Dampers, and Tuned Liquid Dampers. The primary purpose of this research is to decrease structural damage by minimizing the demand for main structural elements through the use of passive energy dissipation devices, particularly, in the form of Yielding Restrained Braces (YRBs) or Inline Friction Dampers (IFDs). Friction dampers dissipate energy through friction and emerge due to the sliding of two solid elements relative to one another. For instance, solid friction can control earthquake-induced vibration, another example on a smaller scale is automotive brakes which dissipate the kinetic energy of motion. The friction damper (brake) is commonly used to extract kinetic energy from a moving body, when a major earthquake occurs, conventional braces buckle which leads to unsymmetrical hysteretic behaviour and loss of stiffness, while the friction damper slips at a predetermined load before yielding occurs in members of a frame, which dissipate a major part of energy. It saves the initial cost of a new construction or retrofitting of an existing building, where the dampers provide a very high energy dissipation. 
\nEven though damping devices can provide supplemental damping to mitigate vibration in buildings due to wind or earthquake effects, integrating them in the design is not often straightforward. For example, building design with inline friction dampers is not directly provided in the Canadian code. The NBCC 2015 contains recommendations for supplemental energy dissipation in general, but no specific provisions are available for friction dampers. In the National Building Code of Canada (2015), the minimum earthquake lateral force in a Seismic Force Resisting System(s) (SFRS) is divided by a reduction factor. This factor, known as the response modification factor, can be calculated by multiplying the overstrength factor (Ro) and the ductility-related force modification factor (Rd). As the 2015 NBCC does not provide the overstrength factor (Ro) and the ductility factor (Rd) for friction-damped systems, engineers usually work with the factor for the closest equivalent system, ductile buckling-restrained braced (BRB) frames (Rd=4, Ro=1.2). This practice is already conservative in nature mainly because the non-damage-based modification factor for a Yielding Restrained Braced (YRB) system has been found to be substantially higher, and because the system can be tested at Maximum Considered Earthquake (MCE) ground motion forces and displacement in contrast to the equivalent systems that cannot avoid uncertainty in their actual behavior. 
\nThe objectives of the present research are to (i) investigate the life safety performance of different concrete moment resisting frames (CMRFs) considering supplemental damping to estimate seismic response factors, (ii) evaluate seismic design parameters of concrete moment resisting frames (CMRFs) equipped with different energy dissipation systems to understand the relative performance of YRBs, (iii) collaborate experimental work with simulation to investigate dynamic performance and reliability of YRBs under real earthquakes, (iv) develop a set of guidelines for the use of yielding restrained braces in concrete frame buildings.
\nIn order to achieve the above goals, a set of buildings with concrete moment resisting frames have been considered. These frames were designed for high seismic locations in Canada and the equivalent locations in the US. The design YRB systems for these frames have been adapted from ASCE/FEMA guidelines and contextualized for Canada. The results show that such an approach could be beneficial for designing buildings with inline friction dampers and could provide not only cost savings but also, enhanced seismic safety and maintainability.

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