# Influence of Multiple Openings on Reinforced Concrete Outrigger Walls in a Tall Building
## 1 Introduction  
With the development of tall building structures, the outrigger system has become one of the most popular structural systems that control the lateral displacement of such buildings. Several researchers and engineers have been studying and developing the outrigger system because it performs well in controlling the lateral displacement at the top of a tall building by reducing the overturning moment [1]. For example, the Shanghai Tower, Hong Kong IFC2, and Taipei 101 are successful applications of the system in tall buildings [2]. Most of the previous research studies focused on the optimum location of outriggers and lateral stiffness of the whole structure. [PERSON] [3] assumed a rigid outrigger beam for single-outrigger structures, and proposed that the optimum location of an outrigger is 0.455 of the total height from the top. [PERSON] and [PERSON] [4] proposed that the optimum locations for two outriggers are 0.312 and 0.685 of the total height from the top based on [PERSON]'s research. [PERSON] and [PERSON] [5] presented generalized results for optimum locations in multi-outrigger structures by assuming rigid outriggers in flexure. [PERSON] and [PERSON] [6] proposed equations for the optimum locations of outriggers by considering their flexibility. [PERSON] and [PERSON] [7] considered the bending and racking shear stiffness of the outrigger truss to determine the optimum location of the outrigger. The research studies on outrigger-braceed structures have been summarized and some further studies have been attempted by [PERSON] and [PERSON] [8]. Recently, [PERSON] et al. [9] proposed a dual-purpose outrigger system to reduce the lateral displacement and differential column shortening. Even though some researchers assumed equivalent beams for the outriggers to derive equations for the optimum locations, most of the outriggers built were made of steel trusses. Although there are a few applications of reinforced concrete outrigger walls, such as Chong Qing Raffles City [10], discussing the walls is not enough. Furthermore, too little attention has been paid to the reinforced concrete outrigger walls with openings. In theory, the deeper the outrigger, the stiffer the structure [11]. It means that a deep outrigger, such as an outrigger wall, can provide more effective lateral load-resistance for high-rise structures. At the same time, reinforced concrete outrigger walls can be cost-effective systems because of the same construction procedure as reinforced concrete core walls. However, as large concrete structures, the reinforced concrete outrigger walls are heavy and space consuming. As a result, it is necessary to solve the problems associated with making better use of the space occupied by outrigger walls. In this study, a model for arranging multiple openings on reinforced concrete outrigger walls, as shown in Figure 1, is proposed. Moreover, the study investigates the influence of multiple openings on the stiffness and strength of the outrigger walls and whole tall building structure. Given the aspect ratio of the outrigger walls, they can be designed as deep beams with openings. [PERSON] and [PERSON] [12] proposed a shear strength equation for deep reinforced concrete beams with web openings. [PERSON] et al. [13] have predicted the capacity of deep beams with openings using the strut-and-tie model. [PERSON] and [PERSON] [14] paid more attention in the evaluation of the ultimate shear strength of deep beams, but there was only an opening in every shear region while the opening is  
Figure 1: A typical tall building structure with reinforced concrete outriggers walls with multiple openings. placed in the critical load path. Although several studies have been performed on deep beams with web openings, there are still difficulties in predicting the structural behavior of deep beams with multiple openings. In this study, analytic equations used to predict the internal shear forces on outrigger walls due to the lateral loads are derived and the results are verified through numerical examples.