大内跨小边跨框架结构预应力筋优化布置方法

Optimizing profile arrangement of prestressing tendons in frames with interior large-span neighboring two exterior small-spans

预应力筋的优化布置是大内跨小边跨的多跨预应力混凝土框架结构合理设计计算的关键.为满足控制截面承载力最大的需要,以往常将大跨所需预应力筋布置为连续曲线,并按水平直线延伸通过其相邻的两小跨,按这种布置方式仅使大跨内产生竖向向上的预应力等效荷载,可较好平衡大跨的竖向外荷载;而若将大跨及相邻的两小跨统一考虑,预应力筋按连续曲线布置,张拉产生的预应力等效荷载不但可有效平衡大跨的竖向外荷载而且也可平衡小跨的竖向外荷载,可以使荷载平衡得到优化实现.以一典型工程为例,分析了在相同条件下两种预应力筋布置过程中张拉引起的综合弯矩、主弯矩和次弯矩的分布和量值上差异,比较了两类布筋形式对正截面承载力计算结果的影响,验证了对大内跨小边跨框架结构统一考虑后整体上按三段连续正反抛物线预应力筋布置的合理性.

Optimizing arrangement of prestressing tendons is a crucial aspect for calculation and design of frames with interior large-span neighboring two exterior small-spans.To maximize the capacity of critical section, prestressing tendons required in interior large-span are often arranged as continuous curve and extended as horizontal straight line to the side columns in two neighboring small-spans.This arrangement generates only upward prestress equivalent load in interior large-span, which could balance the vertical load in interior large-span effectively.While both of interior large-span and two neighboring exterior small-spans were concerned together as a single flexural member, and prestressing tendons were arranged as continuous curves, thus the equivalent load due to tensioning tendons would effectively balance the vertical loads both in interior large-span and two exterior small-spans.This arrangement can optimally realize the concept of load balancing.For a typical project, the differences in distribution and amplitudes of combination moment, major moment and second moment between two types of prestressing tendon profiles under the same conditions were analyzed.The influences on flexural capacity of normal section of two profiles were compared, and the rationality of continuous multi-curvature parabola profile in frames with interior large-span and neighboring exterior small-spans was validated.