Abstract
AbstractPassive control systems, such as buckling‐restrained braces (BRBs), have emerged as efficient tools for seismic response control of new and existing structures by imparting strength and stiffness to buildings, while providing additional high and stable energy dissipation capacity. Systems equipped with BRBs have been widely investigated in literature; however, only a deterministic description of the BRBs’ properties is typically considered. These properties are provided by the manufacturer and are successively validated by qualification control tests according to code‐based tolerance limits. Therefore, the device properties introduced within the structure could differ from their nominal design estimates, potentially leading to an undesired seismic performance. This study proposes a probabilistic assessment framework to evaluate the influence of BRBs’ uncertainty on the seismic response of a retrofitted RC frame. For the case study, a benchmark three‐story RC moment‐resisting frame is considered where BRBs’ uncertainty is defined compatible to the standardized tolerance limits of devices’ quality control tests. This uncertainty is implemented through a two‐level factorial design strategy and Latin hypercube sampling technique. Cloud analysis and probabilistic seismic demand models are used to develop fragility functions for the bare and retrofitted frame for four damage states while also accounting for the uncertainty in the property of BRBs. Risk estimates are successively evaluated for three case study regions. The results show that, for the considered case study structure, these uncertainties could lead to an increase of fragility up to 21% and a variation in seismic risk estimates up to 56%.
Highlights
The damage experienced during historic and recent earthquakes worldwide has continued to highlight the substantial seismic vulnerability of existing reinforced concrete (RC) buildings designed before the introduction of modern seismic2488 wileyonlinelibrary.com/journal/eqeEarthquake Engng Struct Dyn. 2021;50:2488–2509.codes.[1,2,3] there is an urgent need for reliable retrofit strategies of such low-ductility RC structures to effectively increase their seismic safety and resilience.Among the several viable techniques, the use of dissipative braces has emerged to be an efficient retrofit strategy.[4]
buckling-restrained braces (BRBs) have emerged as efficient tools for improving the seismic performance of existing structures
This paper investigates the sensitivity of BRB device parameters and the influence of their uncertainty on the seismic response and fragility of building structures
Summary
The damage experienced during historic and recent earthquakes worldwide has continued to highlight the substantial seismic vulnerability of existing reinforced concrete (RC) buildings designed before the introduction of modern seismic. Among others, buckling-restrained braces (BRBs) are one type of yielding devices where a sleeve provides buckling resistance to an unbonded core that resists the axial stress.[5,6,7] As buckling is prevented, the BRB’s core can develop axial yielding in both tension as well as compression, ensuring an almost symmetric hysteretic behavior This property allows the development of large and stable hysteretic loops, providing significant energy dissipation capacity, and beneficial effects to the structure’s seismic performance. This study focuses on assessing the influence of device-to-device variation allowed by the codes when BRBs are used for seismic retrofitting of existing low-ductility RC MRFs. The present study is performed on a three-story three-bay RC MRF benchmark for which laboratory test data on structural performance under dynamic and cyclic loading for the bare (unretrofitted) frame exists in literature. Seismic risk estimates derived using the upper and lower fragility bounds help evaluate the variation in lifetime risk exceedance probabilities as a consequence of device uncertainty
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