Determination of Reduction Factor for Reinforced Concrete Structures with Coupling Core Wall and Coupling Beams and Comparing with Reinforced Structures with Shear Wall

A coupling beam is a type of beam for connecting two adjacent shear walls, with a functioning similar to that of eccentrically braced steel frames (EBF). Seismic characteristics of various types of coupled beams such as diagonally reinforced concrete coupling beam (DBCB), steel coupling beam (SCB), composite steel/concrete beam utilising a vertical web shear plate with headed shear (SPCB), and steel beam with a steel fuse link located at mid span of the beam (FCB) are studied (Fig. 1). Pushover analysis has been performed for chosen frames of up to 20 storeys in order to determine reduction factor as a function of overstrength factor, ductility factor and indeterminacy reduction factor. In this research, novel relations have been proposed for calculating reduction factor, which include the effect of the type of soil and height of the structure. Four 5-, 10-, 15- and 20-storey frames with 3 m-high storeys and five spans have been analysed. There are four concrete bending frame spans, each 5 m long, and a 4 m-long span with two coupling core wall, each 1.4 m long, and a 1.2 m-long coupling beam. ETABS code [1] has been used for the design of structural members, pushover analysis, and the determination of overstrength factor, ductility factor and indeterminacy reduction factor by which reduction factor can be calculated. The effect of four different types of soil has been considered. Effect of variable parameters on reduction factor In order to investigate the effect of variable parameters on reduction factor, two types of frames, i.e. intermediate and special bending frames, four numbers of storeys, i.e. 5, 10, 15 and 20 storeys, and four different types of soil, i.e. types I, II, III and IV [2], have been considered. The sequence of member stiffness increase is from coupling beams towards beams, columns and shear walls and it is more pronounced for lower frames. By increasing the height of the frame, the reduction factor calculated by the proposed equations is decreased until it coincides with the value proposed by the Iranian Earthquake Code [2]. For points higher than the coincidence point, reduction factor is on the safe side. For looser soils, the value of reduction factor increases slightly for points lower than the coincidence point and it decreases slightly for points higher than the coincidence point.