Behaviors of outriggers in frame-tube structural system of concrete filled steel tube (CFST) tall buildings

The frame-tube structural system is always used in tall buildings and the outriggers are set up to increase the rigidity of buildings and decrease the displacements under lateral loads while they are used to increase the proportion of bending moment from frame columns in the whole structure. The changes in displacement, and inner forces of frame columns during set up of outriggers and rational location of outriggers are analyzed for Tianjin communication building, and Shenzhen SEG Plaza building. The main conclusions are: 1) the space model should be used because the calculation error is larger if the frame of outriggers is analysed using the plane model; 2) The number of outriggers is changed with the height of building, 3 to 4 outriggers are reasonable for building of about 200 m tall; and 4 to 5 outriggers are reasonably for building of about 300 m tall. The location of outriggers should be considered together with the location of technical equipment stories. 3) No outrigger should be located on the top story of building if the outrigger number is less than 1 or 2.