## 5 Conclusions  
In this study, the seismic performance of the ordinary RC shear wall system, which is widely adopted for high-rise residential apartment buildings in South Korea, was assessed and an adequate amplification factor to wall shear forces was investigated. Three analytical models composed of five ordinary RC shear walls taller than 60 m were designed for seismic design category D using a performance-based procedure to circumvent limitations on the seismic force-resisting system in KBC 2016. Seismic performance evaluation was performed in accordance with the procedure and criteria of FEMA P695 based on incremental dynamic analysis. A total of four engineering parameters were taken into account, including inter-story drift, plastic hinge rotation angle, concrete compressive strain at the boundary of wall section, and shear force. Based on the result of seismic fragility assessment for the three analytical models, the ordinary RC shear walls designed with a shear force amplification factor higher than or equal to 1.2 can meet the performance criteria on collapse probability and the collapse margin ratio. Implications obtained for limited conditions of this study are summarized as follows. Figure 17: Seismic fragility curve for individual engineering demand parameters (EDPs) and acceptance criteria (Model A). 1. The shear force of individual walls at each story is the primary engineering demand parameter contributing to the collapse probability most significantly when the shear force amplification factor 1.0 is applied to the design of individual walls. However, the collapse of analytical models designed with a shear force amplification factor higher than or equal to 1.2 is governed by flexural failure, determined by plastic hinge rotation angle. Therefore, the amplification factor 1.2 is recommended for the design shear force in the performance-based procedure to prevent brittle failure and the collapse of ordinary RC shear wall systems with regular configuration and rigid diaphragms. However, a 1.5 or higher amplification factor may be required for buildings with irregular configuration or flexible diaphragms due to contribution from higher modes. 2. Component walls with relatively high stiffness tend to fail in shear, given the collapse probability of individual component walls. Therefore, it is recommended that an amplified design shear force at the initial elastic design stage is used, considering the amplification expected in the nonlinear dynamic analysis in order to reduce the number of iterative nonlinear analyses. However, the amplification factor may be reduced for component walls with relatively low stiffness in which shear failure is anticipated to be insignificant. 3. Taller ordinary RC shear walls tend to be less sensitive to the shear force amplification factor than lower walls. In this case, increasing the shear force amplification factor has little impact on performance improvement. Therefore, the shear force amplification factor can be determined considering the primary failure mode. 4. In case of thin walls comprising the majority-part of residential buildings in Korea, it is very difficult to install hoops required for special RC shear walls, because the spacing is smaller than one third of the wall thickness. For buildings higher than 60 m and located at the area of seismic category D, the ordinary RC shear wall system with simple reinforcement details can be adopted as an alternative to the special RC shear wall and designed using a performance-based procedure with appropriate acceptance criteria satisfying required collapse margin as shown in this study. 5. The result of this study is limited to ordinary shear wall structures with regular configurations and rigid diaphragms, since there is a limited number of two-dimensional analytical models. This study can be utilized as a basis for further study, considering the effects of irregular configuration and flexible diaphragms that are present in actual building structures.