Abstract
Due to the low postyield stiffness of buckling-restrained braces (BRBs), multistory buckling-restrained braced frames (BRBFs) subjected to earthquakes are prone to lateral deformations and damage concentrations at certain stories, which is deemed a damage concentration effect (DCE). A series of nonlinear pushover analyses and response history analyses are conducted to investigate the key factors affecting the DCE of BRBFs. Two comparisons of the DCE are performed for different types of structures and different beam-to-column connections in the main frame (MF). These comparisons show that BRBFs equipped with BRBs as the main earthquake resistance system have a more serious DCE than the traditional moment-resisting frame or conventional braced frame and that the MF stiffness significantly affects the structural residual displacement and DCE. Then, parametric analyses are performed to investigate the influence of two stiffness distribution parameters (in the horizontal and vertical directions) on the DCE of a 6-story BRBF dual system designed according to the Chinese seismic code. The results show that increasing the MF stiffness and avoiding abrupt changes in the BRB stiffness between stories can effectively mitigate the DCE of BRBFs. Finally, the correlations between various damage performance indices are analyzed. A low statistical correlation between the peak and residual drift responses can be observed in BRBFs. Therefore, it is recommended that the DCE be considered in BRBF design.
Highlights
A summarized study [1] noted that a buckling-restrained brace (BRB) can prevent buckling under a random seismic force, resulting in excellent ductility and stable hysteretic performance and thereby overcoming the compression buckling shortcoming of conventional steel braces (CBs)
Fahnestock et al [12] performed a series of nonlinear response history analyses (NRHAs) and a hybrid test for a 4-story buckling-restrained braced frames (BRBFs) subjected to two sets of ground motions corresponding to moderate and major earthquakes. e large residual drifts observed indicated one potential drawback of the BRBF system, as these large residual drifts may present significant challenges when seeking to return the system to service after a major seismic event
As c1 increases, the structural initial stiffness increases because of the increased BRB area, while the structural postyield stiffness remains unchanged because of the constant main frame (MF) stiffness. erefore, the structural postyield stiffness ratio decreases as c1 increases, implying that the BRBF stiffness decreases significantly after the BRBs yield when the structure uses a BRB as the main seismic resistance system. c1 mainly measures the ratio of the postyield stiffness to the initial stiffness of the BRBFs
Summary
A summarized study [1] noted that a buckling-restrained brace (BRB) can prevent buckling under a random seismic force, resulting in excellent ductility and stable hysteretic performance and thereby overcoming the compression buckling shortcoming of conventional steel braces (CBs). The seismic performance of buckling-restrained braced frames (BRBFs) has been numerically analyzed and verified via experimentation, with the results showing that the added BRBs are effective in dissipating energy and controlling the interstory drift [2,3,4,5]. Tremblay [20] proposed a dual steel braced frame achieving a stable inelastic seismic response by replacing some CBs with BRBs in CBFs. Simpson and Mahin [21] investigated the seismic performance of several different strongback spine configurations with BRBs. e experimental results showed that spine systems can effectively reduce the concentration of deformations. A series of static nonlinear pushover analyses (NPAs) and NRHAs are conducted to evaluate the DCE
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