Analysis On SRC Frame-RC Tube Structure With Outriggers Based On Sudden-variation Of Internal Force

In recent years, a large number of high-rise buildings as city’s landmarks haveemerged in our country. In order to fit the increasing of high-rise building’s height,traditional reinforced concrete structures have been gradually replaced by steel reinforcedconcrete structures with more excellent performance. In the frame-corewall structure,horizontal outrigger strengthened stories were often set to control its displacement. Butthis design will result in the sudden variety of structural stiffness and internal force, andis also bad for anti-seismic. Therefore, it has important engineering significance tooptimize the setting of strengthened stories in SRC frame-RC tube structure whenemphatically considering the factor of sudden variety of internal force.In this paper, a simplified model based on an actual SRC frame-RC tube structurewith strengthened stories which is at a height of36floors or140.4meters is builded bythe FEA software ETABS. The influences of the number, the position and the stiffness ofsteel truss outrigger strengthened stories on the following mechanical properties of SRCframe-RC tube structure are studied through a comparative analysis of18projects withdifferent variates:(1) natural vibration characteristics of the structure;(2) displacementunder lateral loads;(3) internal forces under7degree earthquake, etc. On this basis, thepreferred option is made between these projects by combining engineering practice, andthe following main conclusions are drawn.Setting the horizontal outriggers in place can effectively increase the lateral stiffnessand reduce the natural vibration period and the lateral displacement of the structure.When the strengthened story is set in the middle height of the structure, the largestsudden variety of internal force under earthquake appears. Multiple strengthened storiesare better for reducing the displacement and the sudden variety of internal force, but theywill cause more shear increases of the core tube and diseconomy. The displacementdecreases more, and the sudden variety of internal force will be more severe with the increase of the strengthened story’s stiffness. Setting a double-height strengthened storycan significantly reduce the sudden variety of internal force. For the example project,setting a strengthened story at0.8H is better for the displacement and the sudden varietyof internal force. In the actual projects, the following relevant conclusions are drawn.Thestiffness of the strengthened story should be smallest while the overall lateral stiffness ofthe structure can meet the demands. And in order to further reduce the sudden variety ofinternal force of the structure under earthquake, the strengthened story may be arrangedas two stories high.