Abstract
The primary focus of this investigation was to analyze sequentially coupled nonlinear thermal stress, using a three-dimensional model. It was meant to shed light on the behavior of Buckling Restraint Brace (BRB) elements with circular cross section, at elevated temperature. Such bracing systems were comprised of a cylindrical steel core encased in a strong concrete-filled steel hollow casing. A debonding agent was rubbed on the core's surface to avoid shear stress transition to the restraining system. The numerical model was verified by the analytical solutions developed by the other researchers. Performance of BRB system under seismic loading at ambient temperature has been well documented. However, its performance in case of fire has yet to be explored. This study showed that the failure of brace may be attributed to material strength reduction and high compressive forces, both due to temperature rise. Furthermore, limiting temperatures in the linear behavior of steel casing and concrete in BRB element for both numerical and analytical simulations were about 196°C and 225°C, respectively. Finally it is concluded that the performance of BRB at elevated temperatures was the same as that seen at room temperature; that is, the steel core yields prior to the restraining system.
Highlights
The strength of buildings in hazardous loading conditions such as earthquake or fire is one of the main concerns for structural engineers
The use of Buckling Restrained Brace systems (BRBs) has expanded in recent decades owing to their supreme structural behavior in earthquakes
A part of the brace whose strength is lower than the other parts, yields first due to a big compression force formed in the BRB components at elevated temperature
Summary
The strength of buildings in hazardous loading conditions such as earthquake or fire is one of the main concerns for structural engineers. The main role of horizontal bracing systems is to sustain wind and earthquake loads on the structures. The use of Buckling Restrained Brace systems (BRBs) has expanded in recent decades owing to their supreme structural behavior in earthquakes. About 60%–70% of the entire length of the core is restrained by the casing [4] In these bracing systems, compression stresses are mainly sustained by the restrained portion of the core. A three-dimensional nonlinear finite element model was developed to investigate the behavior of BRBs at elevated temperature. The thermal responses of brace are shown which include the temperaturetime history on the surfaces and different locations within the cross-section, as well as the structural response such as stress and strain histories of the specimen.
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