Study On Torsion Design For Horizontal Irregular Buildings Under Effect Of Earthquake

Modern high-rise buildings usually occurred with different irregular structure due to the special requirement of function and facade effect. Hereinto, the problem of irregular torsion is especially outstanding and common. The extensibility of these buildings is not very good, so the structural torsional destroy is usually outburst without premonition and lead to grave destroy once earthquake occurred, then we must control the torsion effect of structure during the course of design. JGJ3-2002 controls the structural torsion effect with torsion period ratio and torsion displacement ratio these two indexes. How to satisfy the two control indexes with certain measures during the structural design is inevitable to all structural designers and a hard problem to deal with, so it is quite necessary to implement the research.This paper probes into the effect factors of structural torsion first, and then summarizes research status about torsional problems in and outside of China, as well as expounds the current relative regulations for structural torsion control its defects. Then designs several structural example of different eccentricity, and finds out the change law of structural displacement ratio, story drift ratio, story max displacement, story average displacement, inter-story displacement angle and interlayer plane torsion angleθaccording to the floor. Finally, deduces out the relationship between displacement ratio and plane torsion angle as well as the relationship during the torsion indexes under the effect of horizontal earthquake.The results coming from the analysis and research above are as follows:①The displacement ratio can usually not satisfy the regulations in the lower floors of high-rise building structure which is plane and irregular, while the torsion effect is not very outstanding. The reason is torsion ratio is a relative index, the average displacement will reach zero much faster than the max displacement if plane max displacement and average displacement are both small, the displacement ratio maybe very large and more than the limit value under this condition, lead to lose the meaning of torsion control.②This paper deems that the plane torsion of structure relates to interlayer plane torsion angleθdirectly, and interlayer plane torsion angleθis a absolute index, it is a torsion angle between the top and the bottom of same floor. We will see form the chapter 3, the displacement ratio of lower floors is overrun, while the interlayer torsion angle, interlayer max displacement, interlayer average displacement and max interlayer displacement angle are all not big, in contrary; the torsion angle of intermediate layer is bigger, while the displacement ratio is small.③The provided period ratio of JGJ3-2002 are wrong in most of time, if the value of T1 is high, the Tt must be high too; if the value of T1 is low, the Tt must be lower. While the literature indicates that there is certain relation between the period ratio and displacement ratio. As to torsion, the scope of structural plane torsion will be reflected directly by structural interlayer angleθ. This paper suggests that the provision about period ratio can be canceled.