Seismic upgrade of deficient RC frames using different configurations of eccentric steel braces
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ORIGINAL PAPER
Seismic upgrade of deficient RC frames using different configurations of eccentric steel braces Muhammad Shoaib Khan1 · Abdul Basit1 · Ubaidullah Khan2 Received: 14 September 2020 / Accepted: 2 November 2020 © Springer Nature Switzerland AG 2020
Abstract Deficient reinforced concrete frames in many developing countries need upgrade and effective retrofitting techniques to enhance the strength, stiffness and energy dissipation capacity of the system. This paper presents eccentric steel braces (ESB) retrofitting technique for deficient reinforced concrete moment-resisting frames. A hollow box steel brace was connected to the beam at different lengths from the beam-column joint that is at Lbeam/8, Lbeam/6 and Lbeam/4. A nonlinear static analysis was carried out on three-story deficient and ESB retrofitted frames and the force–deformation hysteretic response was noted. The ESB retrofitted frames considerably changed the lateral forces load transfer path and as a result increased the strength, stiffness and hysteretic damping of the frames as opposed to the deficient bare frame. Furthermore, a dynamic time history analysis was performed on five and seven-story ESB retrofitted frames and story drift demands were identified. ESB retrofitted frames significantly reduced story drift demands as compared to bare frames. Keywords Seismic strengthening · Deficient frames · Reinforced concrete · Eccentric steel braces · Static analysis · Dynamic analysis
Introduction Reinforced concrete moment resisting frames are used throughout the world, especially in developing countries because of the easy availability of the construction materials and low cost of construction associated. However, on the other hand, numerous construction defects exist in developing countries like Pakistan such as low strength concrete than the design strength, under-/over-sized reinforcing bars, providing of stirrups/ties at a larger spacing in beams/columns, no confinement reinforcement in the beam-column joints and provision of lap splices in the critical regions (Badrashi et al. 2016; Rizwan et al. 2018). Reinforced concrete structures, if not properly designed, detailed and constructed can lead to a catastrophic failure and subsequent human and economic losses upon subjection to earthquake
* Muhammad Shoaib Khan [email protected] 1
University of Engineering and Technology (UET), Peshawar, Pakistan
CECOS University of IT and Emerging Sciences, Peshawar, Pakistan
2
strong ground motions (Ates et al. 2013; Erdil 2011; RuizPinilla et al. 2016; Rossetto and Peiris 2009). In many existing buildings in the developing countries, the aforementioned construction defects exist and therefore need effective, efficient and economical retrofitting techniques to enhance the strength, stiffness and energy dissipation capacity of the system. In the past, researchers have proposed a variety of retrofitting techniques, however, the major techniques are; strengthening of the selective deficient structural elements for example through jack
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