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Steel multi-tiered concentrically braced frames (MT-CBFs) represent a bracing configuration where two or more concentric bracing panels are stacked between the ground and roof levels in tall single-storey buildings. A large proportion of MT-CBFs in Canada are located in low-to-moderate seismic regions (seismic category 0–3) where limited ductility CBFs are often preferred in design. Nevertheless, brace tensile yielding may not occur in all tiers of such frames. Additionally, the analysis and design procedure adopted by the 2019 Canadian steel design standard (CSA S16-19) can become tedious in tall frames with multiple panels. In this paper, the seismic behaviour of limited ductility MT-CBFs in moderate seismic regions of Canada is examined to propose a simplified design method. A set of 16 prototype MT-CBFs is designed in accordance with CSA S16-19, excluding the design requirements prescribed for MT-CBF columns. Nonlinear dynamic analyses are then performed to examine their seismic response. Finally, an efficient design method is proposed in the framework of CSA S16-19. [ABSTRACT FROM AUTHOR]

This paper introduces and assesses the seismic and collapse behavior of a new lateral load-resisting system referred to as steel Moment-Resisting Knee Braced Frame (MKF). A design method following the Performance Based Plastic Design (PBPD) procedure is proposed to analyze the structure and size the structural members. A prototype frame part of an office building located in Vancouver, British Columbia, Canada is then selected to demonstrate the design method and evaluate the performance of the proposed system. The prototype MKF is also designed using the conventional elastic approach in accordance with the National Building Code (NBC) of Canada. The seismic performance and collapse response of the proposed system are examined using the nonlinear static analysis, nonlinear response history analysis (NLRHA) and incremental dynamic analysis (IDA) performed on the prototype five-story MKF under potential sources of seismicity in the west coast of Canada including shallow crustal, subduction interface and subduction intraslab events. Fragility curves are finally developed using results of the IDA to obtain the collapse probability of the system. The results of the analyses are compared to those obtained from a steel Moment-Resisting Frame (MRF) counterpart designed in accordance with the PBPD and elastic approaches. Findings of the study show that the proposed steel MKF can efficiently satisfy the code-specified story drift limit and manifest the yielding mechanism assumed in design. The MKF designed according to the PBPD approach offers the lightest structure among all frames studied and yields a collapse probability lower than that of the MKF designed as per the elastic design method. The proposed system can be used in seismic design of steel multi-story buildings as an alternative to conventional steel MRFs. • A new steel lateral load-resisting system referred to as Moment-Resisting Knee Braced Frame (MKF) is introduced. • A Performance-Based Plastic Design method is proposed to design the system. • The seismic performance of proposed MKFs are evaluated and compared to conventional steel MRFs. • Compared to steel MRFs, the proposed MKF offers similar lateral stiffness and collapse behavior with reduced steel tonnage. • MKF can be considered as a viable alternative to conventional steel MRFs in multi-story buildings. [ABSTRACT FROM AUTHOR]

Single-storey braced steel frame buildings (SSBSFs) are currently the most widely used commercial structures, which include strip malls, power centres, warehouses, small and medium-sized industrial plants. The lateral seismic or wind forces acting on such low-rise structures are usually transferred from a metal roof-deck diaphragm to a system of vertical bracing members. Because these flexible roof diaphragms have a considerable effect on the dynamic response of SSBSFs during an earthquake, they also play an important role in the evaluation of the fundamental vibration period, a key parameter in determining the magnitude of the design seismic forces. It is therefore of utmost importance to reliably predict the fundamental period of SSBSFs. This paper presents the results of a four-year field measurement research project on the dynamic behaviour of SSBSFs. The goal of the project was to create a reliable database for the dynamic characteristics of SSBSFs (periods, mode shapes, and damping) and to find a relationship between them and the geometric parameters (height and plan dimensions). The field tests are described, along with the selected buildings and experimental setup. The measured fundamental periods are then compared to the National building code of Canada (NBCC) empirical equations. A statistical analysis of the data, based on different regression models, yielded new proposed building geometric parameters to be used in simple equations for the prediction of the fundamental period of SSBSFs. [ABSTRACT FROM AUTHOR]