Reinforced concrete (RC) walls have been widely used in tall building construction to resist lateral loads. However, RC walls behave low ductility and limited deformation capacity under high axial force ratio. Due to the brittle behaviour of high-strength concrete, it was seldom used in RC walls though it has a vast of merits compared with normal-strength concrete. To further push up the limit of concrete strength, i.e., beyond 80 MPa in practical wall construction and to figure out a possible alternative of river sand due to the sustainability and environmental friendly requirement, an innovative wall, namely ring-stirrup concrete-filled-steel-tube (CFST) composite wall with high-strength manufactured sand concrete is proposed. The proposed composite wall consists of two CFST columns embedded at each boundary element and several stirrups in the form of continuous ring along the entire section. A series of quasi-static tests based on orthogonal experimental design method (Taguchi method) are conducted to investigate the seismic behaviour of the composite walls. The experimental parameters are axial force ratio, steel ratio in CFST columns and volume ring-stirrup ratio. From the experimental tests, it is concluded that the proposed confining schemes are highly effective in improving the seismic behaviour of the walls. Moreover, the effects of these three parameters on the peak strength, ductility and energy dissipation capacity of the walls have been investigated. Finally, a design approach considering the confinement effect of CFST columns is proposed and verified to evaluate the lateral load-carrying capacity of the proposed walls.

Introduction

Traditionally, reinforced concrete (RC) walls have been adopted in tall building construction thanks to their high lateral stiffness and strength. Research studies [1–۴] have revealed that RC walls behave low ductility and limited deformation capacity under high axial force ratio, which is defined as compressive axial force acting on the wall to the load-carrying capacity (concrete compressive strength multiply the gross section area of wall) ratio when subjected to lateral cyclic loads. Mainly two types of approaches have been adopted to solve these problems formerly. The first one is to limit the axial force ratio, which is commonly adopted in current seismic design code [5–۷]. As an example, Chinese Code for seismic design of buildings [7] suggests that the design axial force ratio should be smaller than 0.5 for tall buildings in severe seismic zones. One of the consequences by adopting this method is the increase in the size of the wall, especially in the lower floor of tall buildings, which occupies the usable floor area and is undesirable for engineers and architects. The second one is to change the configuration and reinforcement details of the wall, especially in the wall boundary, as suggested by design codes [5–۷]. This can be achieved by providing transverse reinforcement (or stirrup) at close spacing to confine the concrete core in this special area. However, due to the arching action [8], the concrete core cannot be fully confined.