Elastic Stability Of High-Rise Structural Systems

As more and more high-rise structures were built in the past decades, researchers had done lots of studies on high-rise structural systems, and the theories are comparatively perfect. However, understanding the overall stability of a structure is not an easy task. Fortunately, current designers have computer software to analyze it. Based on reasonable simplification, this thesis analyzed the overall stability of several different high-rise structure systems, accurate or approximate buckling load expressions are obtained, the stability behaviors of these structures are illustrated.The second chapter analyze a simplified model of double-outrigger-braced structure, a model composed of independent rotational spring and relative rotational spring is proposed for the outrigger-column systems. The critical buckling equation is presented where the axial force of the core and the exterior columns may be varied. By analyzing a specific example, the second chapter reveals the total buckling load of each mega-story is independent of the load distribution among the core and the exterior columns. The analysis reveals also the strong inter-story interaction of the double-outrigger braced structures. By comparing the buckling of the normal frame and the double-outrigger-braced structures, and also by using the approximate buckling analysis based on the negative stiffness concept of gravity loads, which is very successful in normal frame buckling analysis, it is concluded that the double-outrigger braced mega-structure is closer to a normal frame in its buckling behavior, although it has a stronger inter-storey interaction than normal frames.Using the continuum model, the third chapter made a study on buckling of coupled shear walls. A closed form solution and an explicit formula for the buckling load are obtained. The form of the formula implies that the coupled shear wall is a kind of dual structural system, and the interaction between two structural components may be elucidated by a series-parallel circuit. Based on this circuit, an explicit expression for the lateral stiffness of coupled shear wall is found and compared with exact solution. Amplification factors of drift, bending moments and axial forces in walls and bending moments in the link beams due to the second order effect are studied and a simple formula for the amplification factor is also provided.Based on the study of coupled shear walls in the third chapter, the forth chapter studies the stability problem on coupled shear walls with cross section and axial force varies uniformly through the height. Using energy method, shear and flexural deformation curve are assumed to simulate the real buckling deflection curve. It is proved that coupled wall structure behaviors more complicated than a single shear or flexural system. Then a fitted buckling load expression is given, which has a fine accuracy.The fifth chapter pays attention on studies of mega frame structure. Several model are established to analyze and illustrate the nature of stability of mega frame structure. Mega frame structures with single and double storey are presented. The interaction behavior between mega stories are explained. Then a simplified method of solving buckling load of mega frame structure is proposed, which could be a estimation for design work.The sixth chapter analyze at first the buckling of frames with one suspended storey, closed form solution was obtained. Mega-frames with multiple suspended storeys were then studied using the continuum method, equilibrium differential equation for buckling was established. It was found that the stability of suspension mega frames is the same as the frames supporting the gravity loads at the same level at the mega columns. Using the energy method, an approximate expression for the buckling load of columns rotationally restrained at two ends is presented, its accuracy was verified by EFM. For suspension frames with two mega storeys, an elementary algebra method is proposed to solve for the buckling loads an the interaction between two storeys, its accuracy is also verified using numerical analysis.