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Thesis defences

PhD Oral Exam - Ali Naghshineh, Civil Engineering

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

DATE & TIME
Monday, November 29, 2021 (all day)
COST

This event is free

ORGANIZATION

School of Graduate Studies

CONTACT

Dolly Grewal

WHERE

Online

When studying for a doctoral degree (PhD), candidates submit a thesis that provides a critical review of the current state of knowledge of the thesis subject as well as the student’s own contributions to the subject. The distinguishing criterion of doctoral graduate research is a significant and original contribution to knowledge.

Once accepted, the candidate presents the thesis orally. This oral exam is open to the public.

Abstract

The primary purpose of passive energy dissipation devices is to decrease structural damage by minimizing the demand for main structural elements. Advanced structural dissipation systems can be classified into three major groups including seismic isolation, passive energy dissipations, semi-active and active control. Passive energy dissipation devices may be divided into six groups as Metallic Dampers, Friction Dampers, Viscoelastic Dampers, Viscous Fluid Dampers, Tuned Mass Dampers, and Tuned Liquid Dampers. While all these technologies play an important role in structural design, the focus of this report is on Friction dampers, particularly, in the form of Inline Friction Dampers (IFDs) or bracing, which could be categorized as Yielding Restrained Bracing YRB). Friction dampers dissipate energy through the 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. To extract kinetic energy from a moving body the friction brake is widely used. When a major earthquake occurs, conventional braces buckle which leads to unsymmetrical hysteresis behavior 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.

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 (Galindo, et al. 2019), and because the system can be tested at Maximum Credible Earthquake (MCE) ground motion forces and displacement in contrast to the equivalent systems that cannot avoid uncertainty in their actual behavior.

The objectives of the present research are to (i) investigate the 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.

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