考虑预应力筋拉应变滞后的混凝土构件使用性能计算模型

The current calculation theory of crack width and stiffness regards the post-tensioned bonded prestressing tendons as high-bond steel bars, thus the fact that the tensile strain increment of prestressing tendons after decompression lags behind the tensile strain of non-prestressing steel bars at cracking section of concrete members is covered. Complied with the actual situation of widely disseminating and applying high-strength steel bar in our country at present，according to the static loading test of concrete members with 500MPa steel bars, combined with the tensile strain lagging coefficient of prestressing tendons which is deduced in detail and verified by test means and numerical simulation method, the calculation model of crack width and stiffness of concrete members with high-strength steel bars is mainly investigated considering tensile strain lagging of prestressing tendons in this project. The influence which the diameter and cover of surface steel bars have on crack width and stiffness is studied. The mechanism which stirrups have effect on crack is disclosed, the reasonable spacing values of stirrups is suggested. The development of crack patterns is analyzed, the transformations of crack width at different locations are proposed. The unified models for crack width and stiffness of prestressed and non-prestressed concrete members are constructed. The achievements of project can provide reference for improving the present calculation theory of crack width and stiffness, and also are of great practical value for perfecting the serviceability regulations of the current code for design of concrete structures in our country.

当前的裂缝宽度和刚度计算理论将灌浆的后张预应力筋视为高黏结钢筋，因而掩盖了混凝土构件开裂截面处消压后的预应力筋拉应变增量要滞后于非预应力筋拉应变这一事实。为此，本项目顺应我国现阶段大力推广应用高强钢筋的现实情况，拟根据配置500MPa钢筋的混凝土构件静力加载试验，结合详细推导并通过试验手段和数值模拟方法加以验证的预应力筋拉应变滞后系数，重点研究在配置高强钢筋的情况下、考虑预应力筋拉应变滞后的混凝土构件裂缝宽度和刚度的计算模型问题；探讨表层钢筋的直径及其保护层厚度对裂缝宽度和刚度的影响；揭示箍筋影响裂缝的机理，给出箍筋间距合理的建议值；分析裂缝的形态发展，提出不同位置裂缝宽度的换算关系；构建预应力和非预应力混凝土构件相统一的裂缝宽度和刚度计算模型。项目研究成果可为改进目前的裂缝宽度和刚度计算理论提供借鉴参考作用，对完善我国现行混凝土结构设计规范在使用性能方面的规定，亦具有重要的实用价值。

我国现行《混凝土结构设计规范》的裂缝宽度和刚度计算理论，将灌浆的后张有黏结预应力筋视为高黏结钢筋，从而掩盖了混凝土受弯构件开裂截面处消压后的预应力筋拉应变增量要滞后于非预应力筋拉应变这一事实。针对现行规范的这一不足，同时顺应我国现阶段大力推广应用500MPa高强钢筋的现实情况，本项目首先基于已有文献的研究思路，根据裂缝间钢筋平均应变符合平截面假定，分别考虑预应力筋与非预应力筋处于相同和不同水平位置处，详细推导了裂缝截面处后张有黏结预应力筋的拉应变滞后系数。其次，结合中美欧混凝土结构设计规范的裂缝宽度和刚度计算规范比较结果，借鉴其中精度较好的裂缝宽度和刚度计算模式。最后，进行配置 500MPa 高强钢筋的混凝土受弯构件静力加载试验，并收集整理大量已有的短期裂缝宽度和挠度试验数据，研究在配置高强钢筋的情况下、考虑预应力筋拉应变滞后的混凝土受弯构件裂缝宽度和刚度的计算问题，构建预应力和非预应力混凝土构件相统一的裂缝宽度和刚度计算模型。项目研究成果可为改进目前的裂缝宽度和刚度计算理论提供借鉴参考作用，对完善我国现行混凝土结构设计规范在混凝土受弯构件使用性能方面的规定，亦具有重要的实用价值。