Analysis of Tripod shaped high rise building using Tubed Mega Frame structures

Sammanfattning: Most of the tall buildings that are built today have a straight and vertical shape, because vertical buildings are more stable and easily built than slanted ones. In the case of vertical building, bending moments in the base only exists from horizontal loads such as wind and seismic loads, but in slanted buildings there will also be bending moments from dead and live loads. In addition, transportation inside the building is also a challenge when it comes to slanted buildings. However, a new elevator system that ThyssenKrupp has developed will solve that problem. This new elevator has an ability to move in all direction both vertically and horizontally. The new structural system, Tube Mega Frame (TMF), has been studied and proved to have better efficiency than the central core with outriggers. Moving the bearing structure to the perimeter of the building, gives smaller overturning moment and better stability due to longer lever arm from the center. This thesis focuses on applying the Tube Mega Frame system to a slanted building which has a tripod structure. Different types of TMFs were used to compare the efficiency of the buildings performance. The TMF contains perimeter frame and mega columns with different binding systems such as belt walls and bracings. A pre-study has been carried out in order to see the overall behavior of the tripod shape. Different heights and inclinations have been analyzed with stick models. The analysis has been performed in the finite element software SAP2000 and deflections due to dead load was compared. The buildings with least deflection considering maximum height and maximum inclination was chosen for further model analysis in finite element software ETABS. Furthermore, a short study of different bracings system has been performed for the lateral loads and it concluded that X-bracing have better performance. The main study of this thesis focused on the two building models of 450 m with 7° inclination and 270 and 15° inclination. For each model, five different TMF systems were applied and analyzed. The TMF includes perimeter frame, perimeter frame with belt wall, mega columns, mega columns with belt wall and mega columns with bracings. Deformations due to wind load, seismic load and modal vibration has been compared. It concluded that the least deformation is achieved by the TMF mega columns with bracings for both models with two different heights. The periods of the building are comparatively lower than other systems. The deflection from TMF mega columns with belt walls did not differ much from the TMF mega columns with bracings. For the 270 m high building, the top story displacement was remarkably small because of the three legs, making it stiffer and stable. Even with the p delta effect, there were only millimeters of difference in top story displacement. TMF perimeter frame had a lower deflection than with belt wall, which should have been exact opposite. The reason was while making the total volume of buildings equal, the addition of belt walls led to thinner columns in the perimeter and lower stiffness.