Global Analysis of Tall Buildings with Tubed Mega Frame Structures

Abstract: Today, tall buildings are generally built with a central core that transfers the loads down to the ground. The central core takes up a large part of the floor space and there is less room for the actual purpose of the building, such as offices and apartments. The consequence of this is also less rental profit. At a certain height of the building, the central core will not alone manage to keep the building stable. Therefore it needs to be connected with outriggers to withstand the horizontal forces. The Tubed Mega Frame system developed by Tyréns is designed without the central core and the purpose is to transfer all the loads to the ground via the perimeter of building, making the structure more stable since the lever arm between the loads is maximized. The system has not yet been used in reality. This thesis aimed at testing the efficiency of the Tubed Mega Frame system against conventional systems for tall buildings. Two different types of the Tubed Mega Frame system were evaluated; TMF Perimeter frame and TMF Mega columns. To begin with, a pre-study was carried out with the purpose of comparing wind deflections and eigenmodes of several conventional systems and Tubed Mega Frame systems. The buildings were modeled in the finite element software ETABS. The Core, outrigger and perimeter frame system performed best compared to the other conventional systems and was therefore chosen as the conventional system to be tested in the main study. A comparison of the Core, outrigger and perimeter frame system and eight different configurations of Tubed Mega Frame systems was carried out for several different building heights as a main study, based on the tall building 432 Park Avenue, New York. The deformations due to wind and seismic loading and eigenmodes were compared. Furthermore, the models were controlled for tension at the base and Pdelta convergence. Overall the TMF Perimeter frame systems had the smallest deflections as the building height was increased and could be increased the most without reaching tension at the base. As the top story height of the buildings was increased, the Tubed Mega Frame systems outperformed the conventional system. For the TMF Perimeter frame system it could be seen that belt walls were more efficient than cross walls, and for the TMF Mega columns the smaller the distance between the belt or cross wall levels was, the less deflection was achieved. The Core, outrigger and perimeter frame system could be increased to 859 m in height before collapse and the Tubed Mega Frame system that performed best – TMF: Perimeter frame single story belt walls – was increased to 1024 m in height until divergence was achieved.