Development and Performance Evaluation of the Steel Moment-resisting Knee-braced Frame System Under Seismic and Wind Loads
Creators: Mokhtari, Mahdi
Publisher: name: University of Alberta Library
Year: 2024

<p>The primary goal of this Ph.D. project is to develop an innovative steel lateral load-resisting system (LLRS), referred to as the Moment-resisting Knee-braced Frame (MKF), to resist wind and earthquake loads. This system is proposed as an alternative to conventional steel LLRSs for applications in multi-storey buildings. Specifically, this research aims to develop analysis and design procedures for the MKF, using numerical simulations, and provide insight into collapse performance under seismic and wind loads, as well as earthquake-induced economic losses.<br>
In the first phase of the research, a design method following the performance-based plastic design procedure is proposed to analyse MKFs and size the structural members. A prototype frame part of an office building is selected to demonstrate the performance of the proposed system and the design method. The MKF is also designed using the conventional elastic approach in accordance with the National Building Code (NBC) of Canada. The seismic design is performed in the framework of the Canadian steel design standard, CSA S16-19, assuming the formation of plastic hinges at the ends of moment-connected beams and the base of the columns. The seismic and collapse performances of the frames are examined using nonlinear static analysis, nonlinear response history analysis (NLRHA), and incremental dynamic analysis (IDA). Fragility curves are developed and used to study the collapse probability of the system. <br>
The second phase of this study involves the development and verification of the seismic design parameters, including the overstrength-related force modification factor, ductility-related force modification factor, deflection amplification factor, and design period relationship for the MKF system. A set of 14 prototype frames is designed as per the 2015 NBC of Canada. Nonlinear static analyses are then carried out to determine the preliminary seismic design parameters. Six new MKFs (assessment frames) are designed using the proposed seismic design parameters, and their seismic and collapse performances are examined. The results confirm that the MKF shall be designed as a moderately ductile LLRS using overstrength and ductility factors of 1.60 and 3.0, respectively, with a height limit of 40 meters in high seismic regions of Canada.<br>
In the third phase of this Ph.D. project, the earthquake-induced economic loss performance of multi-storey buildings equipped with the steel MKF system was assessed and quantified using a probabilistic storey-based loss estimation procedure. The expected economic losses and the expected annual loss values are then computed and interrogated for six prototype buildings to further our understanding of the structural performance of the MKF. The results indicate that the MKF buildings offer promising seismic loss metrics and that the economic loss of the MKF buildings is governed by non-structural repair costs under frequently occurring seismic events, while collapse and demolition dominate building losses in the case of larger seismic intensities.<br>
The last phase addresses the performance of the MKF system under wind. A 12-storey prototype building equipped with the steel MKF system located in a low seismic region is designed under lateral wind loads per 2020 NBC of Canada. Wind pressure histories consistent with the building aspect ratios scaled to multiple hazard levels are then used to perform NLRHA and IDA to evaluate the response of the MKF at both system and component levels. The results show that the MKF system can meet the serviceability and strength requirements set by the NBC of Canada and ASCE 2019 Prestandard for Performance-Based Wind Design. Furthermore, the MKF system exhibits an acceptable collapse performance with a significant reserve capacity, which can potentially be leveraged for a more balanced wind design with limited inelastic response.</p>