In Frame-wall structural system, the combination of the shear walls and flexural frames resists the lateral load. One of the drawbacks of this system is to reduce the effect of the wall in the upper floors and even its negative impact. One of the systems that is suitable for correcting this problem is the outrigger-braced system. This system increases the effective depth of the structure during cantilever bending, by increasing the axial force coupling in the columns. Outrigger is generally placed on the middle floor of the building. However, it is also possible to create it on the highest floor of the building. In this case, it is called a cap outrigger.
Since the use of an outrigger creates interruptions to the operation of the building, the use of cap outrigger will prevent this problem. But on the other hand, in high-rise buildings, the use of a cap outrigger alone will not be beneficial. Due to the fact that the frame-wall system is used in a wide range of high-rise buildings, this research has examined the effect of cap outrigger and outrigger combination on the behavior of a 40-story frame-wall system building.
The present study showed that when using the cap outrigger, the lateral displacement changed to 87% of the reference model. Using the outrigger on the 20th floor instead of the cap outrigger makes the displacement down to 69% of the reference model. And the combination of cap outrigger and outrigger reduces roof displacement by up to 60% of the displacement of the reference model. The use of a single cap outrigger, a single outrigger, and a combination of a cap outrigger and outrigger, can increase the wall shear by 26%, 39%, and 57%, respectively, than the reference model.