In a core-wall structure with buckling restrained braces (BRB) outrigger, locations of the plastic hinges are influenced by the outrigger action. Therefore, the designer should consider the issue and use suitable details in the plastic hinge area. The essential questions that arise here are the plastic hinge location and the design moment demand used for design of this kind of structure. In this paper, responses of the core-wall buildings with BRB outrigger designed by using the traditional response spectrum analysis procedure are assessed by implementing the nonlinear time history analysis. The result demonstrates that the plasticity can extend over anywhere within the core-walls specially, at the base and above or below the outrigger levels. Formation of three plastic hinges in the core-wall is recognized suitable for the system. To control the plasticity extension in the core-wall, it is recommended that a new modal combination method be applied to calculate the moment strength of the three plastic hinges over the height. A capacity design concept is used to design other regions of the core-wall where the plasticity does not extend to. The proposed procedure improves behavior of the system by restricting the plasticity extension to the predefined plastic hinge regions. levels in the first case. Therefore, placement of the outrigger at 0.5H is not recommended according to the displacement demand.
CAPACITY DESIGN APPROACHThe philosophy of capacity design in structural seismic engineering ensures that during an earthquake, the structure responds in a favorable ductile manner. This is achieved by pre-selecting an appropriate plastic mechanism and then providing special detailing to the plastic hinge regions. Providing enough ductility in these regions leads to energy dissipation under severe earthquakes (Park and Paulay, 1975;Paulay and Priestley, 1992). Capacity design approach can keep the large portion of the core-walls elastic and facilitate the detailing of the reinforcement there. The ease of detailing and reduction in Figure 11. Average of the (a) curvature ductility, (b) moment, (c) shear, (d) inter-story drift ratio and (e) lateral displacement envelop, in 40-story core-wall.
SUMMARYNear-fault (NF) ground motion having forward directivity and far-fault (FF) earthquakes can generate different responses on tall reinforced concrete cantilever walls. In this paper, the behavior of the core wall buildings were examined by performing nonlinear time history analyses on 20-story, 30-story and 40-story fiber element models. The concept of one, two, three and extended plastic hinge in the core walls subjected to the NF motions having forward directivity (pulse-like) and FF motion was studied by carrying out inelastic dynamic analysis. At the upper levels of the walls, NF pulse-like ground motions can produce considerably larger curvature ductility, inter-story drift and displacement demands as compared with the FF motions. A new approach was proposed to obtain the moment demand and reinforcement required to balance the curvature ductility demand along the height of a core wall.
Abstract. In this study, the responses of reinforced concrete core-wall structures connected to the outside columns by Buckling-Restrained Brace (BRB) outriggers in tall buildings were investigated. The buildings were subjected to forward directivity Near-Fault (NF) and ordinary Far-Fault (FF) ground motions. According to the current codes for the DBE level, the response spectrum analysis procedure was applied to analyze and design the structures. The nonlinear ber element approach was used to simulate the reinforced concrete core-walls. Nonlinear time history analysis was implemented using 14 NF as well as 14 FF records at MCE level. In the core-wall, the results showed that the mean moment demand envelope and the mean shear demand envelope obtained from the NF records were approximately similar to the corresponding demand envelopes from FF records. The reason had to do with extending plasticity all over the RC core-wall, which was subjected to both sets of records. The overall responses of the reinforced concrete core-wall with BRB outrigger system were in acceptable range both for NF and FF earthquakes. In this study, the largest curvature ductility demand in the reinforced concrete core-wall took place at levels just above the outriggers.
In this study, different energy components in the tall reinforced concrete core-wall buildings with numerous plastic hinges over the height are investigated using nonlinear time history analysis. The effect of near-fault and far-fault earthquakes is compared. The idea of one-plastic, two-plastic, three-plastic and whole-plastic hinge approaches along the core wall is examined. The input energy, inelastic, damping, kinetic and elastic strain energy during the earthquakes are studied. The results show that a large energy quantity transfers to the structure at the arrival time of the near-fault motion pulse. Inelastic energy distribution over the height shows a considerable amount of inelastic energy dissipation occurring at the base and above the mid-height of the walls.The 20-story, 30-story and 40-story core-wall structures with fixed bases and with a typical story height of 3.5 m are considered here in this research. For the design purpose, a three-dimensional linear 802 H. BEIRAGHI, A. KHEYRODDIN AND M. A. KAFI
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