体外预应力筋的极限应力:既有典型计算方法评述

ULTIMATE STRESS IN EXTERNAL TENDONS: COMMENTS ON THE EXISTING TYPICAL METHODS

该文分析和评述了确定体外预应力筋极限应力的三类计算方法,即:粘结折减系数法、基于截面配筋指标的回归方法和基于变形的方法。分析表明,基于变形的方法能够反映体外预应力混凝土梁所具有的构件截面强度与构件整体变形相耦合这一显著特征。在基于变形方法中的两个常用的等效塑性区长度模型中,与构件跨高比和外荷载作用形式相关联的模型过分夸大了荷载作用形式对体外预应力筋极限应力的影响。针对桥梁结构所承受的移动交通荷载,承载能力极限状态下,实际设计中很难判断和选择与荷载作用形式相关联的系数。而与构件失效时关键截面中性轴高度相关联的等效塑性区长度模型中的关键参数在不同试验中则具有较好的稳定性和一致性。该文的研究结果有助于建立简单而正确的体外预应力筋极限预应力计算方法。

Three methods for the determination of the ultimate stress in external tendons are introduced and commented. They are bonded reduction methods, regression formulas related to reinforcement index and deformation-based methods. It is shown that deformation-based methods can reflect the characteristic of the coupling between the flexural strength and the entire deformation in prestressed concrete members with external tendons. In the deformation-based methods, two commonly adopted models for computing the length of equivalent plastic region are critically investigated. It is found the model based on the span-depth ratio together with loading type places much emphasis on the effects of loading type on the ultimate stress increment in external tendons. In addition, for the ultimate limit state of a highway bridge with moving traffic loads, it is difficult for designers to judge the coefficient which is related to the load type and load arrangement. In contrast, the key parameter in the model based on the neutral axis depth for computing the length of equivalent plastic region, is stable and consistent and can be treated as a constant. The present study can contribute to establishing a simple formula for the estimation of the ultimate stress in external tendons.