非线性阶段预应力次弯矩概念及其在弯矩调幅中的应用

非线性阶段次弯矩的演化，以及承载力极限状态下是否考虑次弯矩的问题一直存在争议。为解决这一问题，拓展了预应力次弯矩的概念，使其能够适用于非线性阶段。运用变刚度法数值模拟了初始次弯矩(M₂)与弹性最大荷载弯矩(M_e)之比为0.15~0.36的15根有黏结预应力混凝土两跨连续梁。基于拓展后的次弯矩概念，提出了以混凝土受压区相对高度、初始次弯矩与弹性最大荷载弯矩之比为影响参数的有黏结预应力混凝土连续梁弯矩调幅公式。采用已有文献中受压区相对高度为0.35的试验梁比较了所提公式和现有的弯矩调幅公式。设计制作受压区相对高度为0.18的两跨预应力混凝土连续梁，获取单调加载下支座反力数据，检验了内力重分布程度较大时所提公式的效果。结果表明，给出的弯矩调幅公式的计算结果偏于安全，且更接近试验结果。

Concept of prestressing secondary moment in nonlinear stage and its application in moment redistribution

The variation of secondary moments in post-elastic range, including whether the secondary moment shall be considered in ultimate limit state calculations, has been a subject of much controversy for many years. Towards a better solution to this problem, the concept of secondary moment due to prestressing is extended into nonlinear stage. By using the method of stiffness variation, fifteen prestressed continuous beams with bonded tendons were numerically simulated in which the ratio of initial secondary moment (M₂) to ultimate elastic loading moment(M_e) was 0.15- 0.36. Based on the extended secondary moment concept, a formula for moment redistribution at the ultimate limit state was put forward with relative depth of compression zone (ξ) and M2/Me as the influencing parameters. A test specimen (ξ=0.35) from literature was analyzed to compare the proposed formula and existing formulas for moment redistribution. A two-span prestressed continuous beam(ξ=0.18) with large degree of moment redistribution was designed and tested under monotonic loading whose support reactions were measured and used in checking the prediction by the proposed formula. It is shown that the proposed formula is conservative and gives predictions that are closer to the test results than the existing formulas.