Global analysis of a tubed structural system for an inclined slender tall building

Sammanfattning: Building engineering is called upon to keep up with the pace and challenges of modern design, which aims not only to build higher and greener, but also to fulfill the demands of the growing population and simple human curiosity. The main purpose of this study was to examine the global behavior of a slender and inclined (V-shaped) 300 m high rise building with different structural systems applied. In order to properly evaluate them, four different parametric studies were conducted. These included determining the appropriate inclination angle and the geometry of a simple beam system and later comparing fourteen different structural systems, namely trusses, diagrids, Tubed Mega Frames and moment frames. Parallel to this, a further investigation was made on a shell and beam element model, in order to assess the simplifications made and to control the obtained results. This study was based on various simulations in Finite Element Analysis programs, primarily ETABS, but also SAP2000 and Autodesk Robot Structural Analysis. The modelling included the definition of geometry and applied loads and results in extracting the desirable forces and deformations. Additionally, the automatic design for structural members was used for the purpose of a comprehensive study of the chosen structural systems. The designed structures were subjected to static analysis (dead, live, wind, seismic load), dynamic analysis (response spectrum and time history function) and nonlinear P-delta effect. A buckling analysis was also performed to determine the modes and associated load factors for buckling. In the end, the structural response in terms of displacement and acceleration was compared. The inclination angle study set the defining angle at 10° from vertical, with respect to the serviceability limit deflection. Comparing alternative truss geometries in a 2D parametric study resulted in the choice of four different systems (X, N, K and W trusses). In the 3D analysis, the chosen truss systems, together with three variations of diagrid systems, and seven Tubed Mega Frames with two moment frame structures were further analyzed. In both groups, the mass and the material of the systems were kept similar and the comparison was basically based on the obtained maximum displacement and natural periods of the buildings. The shell and frame model comparison gave a difference in displacements between 0 and 12%. Finally, the comprehensive study of the Tubed Mega Frame, X truss and diagrid structures showed that these buildings were performing similarly to vertical buildings with a top story displacement within the suggested limits (less than 673 mm). Further investigation should be made concerning the acceleration under synthetic earthquake, which exceeded the suggested norms, as well as the connecting nodes between the trusses and the inclined columns. The outcome of this study implied the possibility of construction and usability of inclined, slender, tall buildings with respect to the Ultimate Limit State and the Service Limit State, as specified in the American standard, ASCE 7-10, and opened new possible issues for further research.