In this research, they found that negative shear lag will change with the different boundary conditions of displacement and external force applied to the girder. In the same year, Chang and Zheng tried to find out more about negative shear lag and its influential factors on a cantilever box girder. In 1969, Fazlur Khan proposed a chart named “structural systems for height” which has classified the different types of tubular systems with regard to their efficiency for high-rise buildings of different heights. Gravity loads are resisted partly by exterior frames and partly by interior columns.
Bending in columns and beams or rotation of the beam-column joint in the web section resists the shear force produced by lateral load. In a framed tube system, the tube form resists overturning produced by lateral load-a leading cause of compression and tension in columns. In a rigid frame the “strong” bending direction of columns is aligned perpendicular to the face, while this factor is typically aligned along the face of the building in a framed tube system. A case in point is that the material consumed in this kind of system is reduced by half in comparison with other systems. Among the most important specifications of tubular systems is their high economic efficiency. The whole system works as a giant vertical cantilever, and its high efficiency is due to the large distance between windward and leeward columns. This type of structural system is mainly comprises closely spaced circumferential columns, which are connected by deep spandrel beams. The framed tube idea is an effective framing system for high-rise buildings. In addition, shear lag in structures with the hexagon shaped plan was at the minimum. It is observed that all types of structures with various plan geometry subjected to the wind load had a greater amount of shear lag factor in comparison with structures subjected to the static and dynamic earthquake loads. Further work is carried out to compare the shear lag factor of these structures with distinct plan shapes against different types of lateral load. Three various plan shapes including rectangular, triangular and hexagon were modeled, analyzed, designed and subjected to the earthquake and wind load, separately. The above relation is not yet considered in previous literatures. In this paper, the possible relation between shear lag and the type of lateral load subjected to these systems is investigated. This anomaly is called “shear lag”, and it is a leading cause of the reduction in efficiency of the structure. When a cantilever tube is subjected to a lateral load, it is expected that the axial stress in each column located in the flange frame of the tube is the same, but because of the flexibility of peripheral beams, the axial stress in the corner columns and middle columns is distributed unequally.
The periphery of the building plan in a tubular system consists of closely spaced columns connected by circumferential deep spandrels. Tubular structures are extensively recognized as a high efficiency and economically reasonable structural system for the design and construction of skyscrapers.
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