无黏结预应力连续梁次弯矩演化及弯矩调幅

完成4根无黏结预应力混凝土两跨连续梁受力全过程试验,对支座反力及控制截面弯矩重分布程度进行分析.运用非线性阶段的预应力次弯矩定义,将非线性阶段连续梁总弯矩分解成次弯矩和荷载弯矩.研究加载全过程次弯矩和荷载弯矩的演化规律,提出了对初始次弯矩和弹性荷载弯矩分别调幅的无黏结预应力混凝土连续梁弯矩调幅公式.采用已有文献中一组试验梁对所提公式的计算精度进行验证.研究结果表明,无黏结预应力连续梁弯矩重分布的原因可以归结为无黏结筋应力的增长以及连续梁各部分割线刚度比值的改变.承载力极限状态下,次弯矩折减系数随中支座综合配筋指数的增大而增大,荷载弯矩调幅系数随其增大而降低.文中弯矩调幅建议公式较已有公式更接近试验结果,可为设计规范中相关条款的制订提供参考.

Variation of Secondary Moment and Moment Redistribution in Prestressed Continuous Beams with Unbounded Tendons

An experimental study was conducted on four prestressed concrete continuous beams with unbonded tendons over entire loading. Support reactions and degree of moment redistribution at critical sections were analyzed. By secondary moment definition in post elastic range, total moment of a continuous beam in nonlinear stage could be decomposed into secondary moment and moment due to external forces, the variation of which over entire loading was studied. Based on revising the initial secondary moment and elastic external load moment separately, a redistributed moment formula for prestressed concrete continuous beams with unbonded tendons at the ultimate limit state were proposed. This formula was verified using a group of test specimens from literature. Results show that, the reason of moment redistribution in prestressed concrete continuous beams with unbonded tendons can be attributed to the stress increase of unbonded tendons and secant stiffness comparison charge between each part of the continuous beam. At the ultimate limit state, the higher global reinforcement indices at the section over inner support, the higher secondary moment reduction factor and the lower external load moment modulation factor. In the prestressed concrete continuous beams with unbonded tendons, the calculated moment of the section over inner support by the proposed formula is closest to the test results than the existing formulas. The proposed formula can provide a reference for the development of design code in relevant provisions.