混凝土箱梁腹板竖向预应力损失的模型试验研究

EXPERIMENTAL STUDY ON THE LOSS OF VERTICAL PRESTRESS IN THE WEBS OF CONCRETE BOX GIRDERS

制作一混凝土台阶梁模拟PC箱梁桥变高度腹板,在梁内安装10根不同长度竖向预应力筋及YGM锚具,测试了竖向预应力各项损失值;同时通过在螺母下放置不同倾角的垫板以模拟锚具安装误差,测试安装倾角误差与预应力瞬时锚固损失的关系;通过改变张拉锚固过程中拧紧螺母施加的扭矩值,得出扭矩、倾角与瞬时锚固损失的关系。测试结果分析表明:除长期损失外,竖向预应力各项损失测试值均大于规范JTGD62-2004计算值。管道摩阻损失与混凝土弹性压缩损失占比重很小,竖向预应力损失主要是由钢筋回缩损失与长期损失组成,其中回缩损失又占绝大部分比例。钢筋的回缩损失与锚具安装误差,螺母拧紧程度存在明显对应关系。施加较大的拧紧扭矩并不能完全消除因锚具安装误差引起的预应力损失,为了减小竖向预应力损失,必须提高锚垫板的安装精度。

A stepped concrete beam was casted to simulate the web of a prestressed box beam with changing height, in which 10 vertical prestressing bars with different length and YGM anchors were installed, so that the test and analysis about various kinds of loss of vertical prestress were done. Pad boards with different inclined angles were plugged under the anchor nuts to analog the fixing error of the anchors, to test the relationship between the fixing angle error and prestress loss of instant anchoring. Besides, the relationship between fixing inclined angle or torque and prestress loss of instant anchoring is analyzed through changing the magnitude of the torque acting on the nut. The outcome show that the testing values of all kind of the loss of vertical prestress except for the long-term loss are greater than that calculated by the formulas in Code JTGD62-2004. The friction loss and the loss due to elastic compression of concrete member take a very small proportion of the total loss. The main loss of vertical prestress is composed by that due to anchorage slip and long-term factors, and the loss due to anchorage slip takes the biggest part. This loss is evidently affected by the fixing error of anchors and the tightening level of the screws. Higher tightening torque cannot evade the loss due to the fixing error of anchors, so the fixing accuracy of anchorage board must be improved.