抗震设计中的平扭耦联问题

偏心率、周期比(结构扭转为主的第1自振周期与平动为主的第1自振周期之比)和位移比(楼层最大水平位移(层间位移)与该楼层两端水平位移(层间位移)平均值之比)是平扭耦联问题中的三个关键参数。中美两国规范都把位移比大于1.2定义成平面不规则中的扭转不规则。但是,两国规范控制扭转效应的侧重点有所不同。美国规范不控制周期比,它对每层的动扭矩作了放大,以考虑扭转不规则对构件内力的影响,强调结构的地震反应和构件的内力;我国规范提出周期比不大于0.85~0.90的限值要求,强调结构的自振特性。本文详细地叙述了结构工程师关心的刚心和质心的定义和计算机求解方法,综合结构的自振特性和地震反应,以周期比、第1振型中的扭平分量比和位移比为控制指标,提出了结构动力规则性概念。明确指出结构的扭转不仅仅是几何规则性问题,本质上它更是一个动力规则性问题。结构可以是几何不规则的,但结构工程师要努力做到结构的动力特性是规则的。文中还列出了实现结构动力规则性的9

Seismic design of tortionally coupled buildings

With regard to the design of torsionally coupled buildings,the three key parameters are eccentricity,ratio of the uncoupled torsional period to the uncoupled lateral period and ratio of the maximum story drift to the average of the story drifts.Both American and Chinese codes define that the torsional irregularity shall be considered to exist when the maximum story drift is more than 1.2 times the average of the story drifts at the two ends of a building structure.However,there exists a difference between the codes when dealing with design and analysis of a torsionally irregular building.In IBC a torsional amplification factor,A_(x),is required to account for the effects of torsional irregularity in calculating internal forces of the elements.In GB 50011—2001,however,the ratio of periods is required to be no more than 0.85-0.90 in modal analysis.This paper explains in detail the definition of mass center and rigidity center,and how to evaluate them by computer.It proposes a concept of dynamic regularity of a building structure in terms of the ratio of periods,the ratio of the maximum story drift to the average of the story drifts and the torsional content in the fundamental modal shape.The characteristics of torsional regularity of a structure are to be expressed not only in geometrical terms,but also in essence of dynamic.A structure could be irregular in geometry.The structural engineers,however,shall design the building to be dynamically regular.Several ways are presented in the paper on how to design and propotion a structure dynamically regular.The author also suggests that new provisions regarding structural dynamic regularity would be included in the current design code.