Force Analysis About Frame-core Tube Structure With Middle Truss Strengthened Stories

With the rapid economic growth and the fast technological development,high-rising buildings are playing an important role in the construction industry.As the diversity of the structure multiplies,new structural forms,such as tube-in-tube structure and frame-core tube structure,have provided firm support to the demand of high-rising buildings.When the height or the stories of a building increase,the seismic effect is no longer negligible.To satisfy loading requirements and the safetyof high-rising buildings under earthquakes,thestrengthened stories are proposed.Strengthened stories effectively bound the displacement of stories of high-rising buildings under external horizontal loadings and carrypart of bending moments once exerted on the core-columns.But the arrangements of the strengthened stories result in abrupt changes of vertical stiffness of the structure,and thus may cause weak stories in the structure.As the strengthened stories have pros and cons,the types of strengthened stories and their layouts shall be studied in multiple aspects.To determine the optimal layout of the middle truss strengthened stories,following works are carried out in this study:Brief introduction of relatedstudies on building construction withmiddle truss strengthened stories,developments of this technique,and concepts and types of the strengthened stories.Brief report on a real-world construction project in Panyu District,Guangzhou,Guangdong.The building in this case adopts frame-core tube structure with 66 stories on the ground and has a height of 271.4 meters which surpasses the standard height limit.The construction in this case is modeled and computed with YJk,meanwhile the ETABS is adopted to re-examine the models.Four models are built,the first model as the baseline which has no strengthened stories,the second with only one at the 1/2 height of the structure,the third with two respectively at the 1/2 height and the 2/3 height,and the fourth with three strengthened stories.The three models with strengthened stories and the baseline model are analyzed using mode-superposition response spectrum method to determine their performances under horizontal seismic loadings.Vibration periods,story drifts,angles between the stories and shearing forces on the bases are compared so as to determine the optimal number and layout of the middle truss strengthened stories.On the optimal arrangement from the comparison,the elastic and plastic time-history analyses are performed under frequent and rare earthquakes,respectively,both using an artificial seismic wave and two natural seismic waves.The relationship between the displacement angles in elastic-plastic and elastic time-history analyses under rare earthquakes is fitted based on the theoretical ground of the relationship between displacements in the two analyses described in Code for seismic design of buildings.In summary,the thesis studies the structural performance of the frame-core tube structure with middle truss strengthened stories,comes to the conclusion for the aforementioned construction project that the optimal configuration is two reinforcing stories at 1/2 height and 2/3 height of the structure,respectively,reveals that the relationship between the displacement angles in elastic-plastic and elastic time-history analyses under rare earthquakes is positively proportional,and finally provides practical and theoretical reference to designs of frame-core tube structure.