IntroductionIn the past three decades, the steel plate shear wall (SPSW) configuration has been widely used as a lateral load resisting system in the regions of high seismicity. A typical SPSW consists of infill steel plates connected to the beams, known as the horizontal boundary elements (HBE); and to the columns, as the vertical boundary elements (VBE). All HBE-VBE connections are of moment resisting type.Many numerical researches have been and are being carried out to study the behavior of SPSW systems via the four available methods of analysis. Two methods are linear, known as Linear Static Procedure (LSP) and Linear Dynamic Procedure (LDP); and two methods are nonlinear, known as Nonlinear Static Procedure (NSP) and Nonlinear Dynamic Procedure (NDP). The linear procedures are appropriate when the expected level of nonlinearity is low. In the SPSW system, the material nonlinearity is considerable as infill plates yield extensively. Therefore, nonlinear methods are proper tools to study the seismic behavior of such system. The nonlinear dynamic procedure, also known as the nonlinear time history analysis, is deemed to be the most accurate method; but it is complex, expensive and time consuming, especially when there are a large number of elements involved. On the other hand, the nonlinear static procedure, known as the pushover analysis, is a more convenient available method to the structural engineers; and is favored by practicing engineers. The nonlinear pushover analysis accounts for both geometric and material nonlinearities in buildings subjected to seismic loads. It also allows the tracing of the sequence of yielding and failure of members, as well as the progress of overall capacity of structures. On the other hand, prior to a cyclic test or analysis, pushover analyses are performed to predict the maximum strength and deformations of structures in order to develop a suitable loading history, evaluate the needs for instrumentation, establish the range of load and deformation measurements, and reduce the risk of unexpected behavior during experiments [1].In addition to the above mentioned applications, the pushover analysis has two further use in SPSW structures. According to the specifications of AISC-341 [2], Comm. F5., 3. Analysis,
The use of capacity design method (CDM) in steel plate shear wall (SPSW) structures results in large vertical boundary elements (VBEs). One way to reduce the force demands on VBEs is to employ outrigger beams in the adjacent spans of SPSW. In this paper, twelve dual SPSW-moment resisting frames are designed and analyzed by FE method to investigate the effects of outrigger system on the behavior of SPSW structures. Results show that outrigger beams can transfer considerable amount of axial force and bending moment from VBEs to the outer spans columns; resulting in smaller sections for VBEs. In addition, the most effective stories to employ outrigger beams are shown to be the stories which undergo larger drifts. Outrigger system also results in a more uniform distribution of structural stiffness along the height of SPSW frames. Furthermore, a design procedure based on the direct analysis method is proposed for the design of SPSW-Outrigger system. The procedure eliminates the excessive capacities in CDM, while satisfying all CDM requirements.
Double-I sections are widely used as columns in moment-resisting frames. The conventional welded moment connection between I-beam and double-I built-up column behaves in a partially restrained manner and does not provide the strength and ductility required in special moment frames. In this paper, a modification method is proposed to improve the behavioural characteristics of conventional moment connections. The modification involves replacing the continuous cover plate with two alternative plates having increased width and thickness at the location of the beam flange-plates. The behaviour of the proposed connection was investigated in detail both experimentally, by means of two full-scale specimens, and analytically, by means of eight finite element models. Based on the results obtained, in beams with a modified connection most of the plasticity develops remote from the column cover plate, and the panel zone remains in an elastic state. Accordingly, the deformation of the modified connection is reduced significantly and its stiffness is increased to the level required for a fully restrained connection. The hysteresis curves of the modified connection are also stable during large inelastic deformations with no substantial pinching. The modified connection provides the strength and ductility required in special moment frames.
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