Innovative Steel Braced Frame Systems for Enhanced Seismic Performance

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Steel braced frames are among the most popular structural systems used to resist wind and earthquake lateral loads imposed to building structures. The system is very effective when responding in the elastic range as is the case under wind and small earthquakes. However, the system has been shown to exhibit poor performance under strong earthquakes such as large plastic deformations and significant permanent deformations. Higher seismic design loads, stringent height limits and other requirements have been implemented in codes to achieve minimum safety to the public. These have increased construction costs and limited the range of application of the system and building owners are likely to face long downtime periods as well as major repair/reconstruction costs after a major seismic event, which will result in major losses for the Canadian economy.*******This research aims at developing new steel braced frame systems exhibiting superior performance with no or limited damage after an extreme earthquakes such that operations can be resumed rapidly and repair costs are minimized. Three systems will be studied: rocking frames with base shear fuses for low-rise applications; modular spine systems for medium-rise buildings and multi-tiered braced frames for tall single-storey applications. These three applications cover nearly the entire range of steel building structures that are built in Canada. The rocking frame will be developed to accommodate seismic imposed displacements through rocking and self-centering shear fuse acting in series such that the demand on each mechanism is limited and the structure sustain no structural damage. The modular spine concept eliminates soft-storey response, allowing steel braced frames to be used in buildings more than 2 times the height limit currently specified in the Canadian code. The system is designed such that inelastic seismic deformations only develop in dedicated elements that can be easily replaced after an earthquake. Hence, the structure sustain no damage, even in very severe earthquakes. Multi-tiered braced frames must now be constructed with much heavier columns to resist the seismic induced flexural demand and prevent buckling failure. Alternative bracing configurations are proposed that require smaller columns while reducing the structure displacements.*******The applicant has originally proposed the three systems and the proposed research aims at completing ongoing development work. For all three systems, the research consists in developing effective structural arrangements, examining their response under strong ground motions using advanced nonlinear seismic analysis, developing design strategies to optimise their response and performing large scale physical testing to demonstrate their performance.******