基于钢束应力测试的预应力混凝土箱梁承载力评估方法

Bearing capacity assessment method for PC box girder by testing stress of tendon

为了解决在役开裂损伤预应力混凝土箱梁桥安全性能的量化评估问题,在局部预应力钢束有效预应力测试的基础上,开展开裂损伤预应力混凝土箱梁桥承载力评估方法研究。首先,基于参数识别与修正思想,将预应力瞬时损失中的摩阻损失和反摩阻损失值用摩阻损失相关参数表示,提出一种基于表层钢束应力推定内层钢束应力的方法,解决预应力混凝土桥梁钢束沿程实际应力分布的量化表达问题。其次,考虑截面受拉区混凝土抗拉强度影响,推导考虑受拉区混凝土开裂影响的截面分析迭代公式,提出迭代求解方法和步骤。最后,开展3片实梁足尺模型试验,采用预应力钢索张力测试仪对开裂损伤的试验梁跨中截面表层钢束进行了应力测试,并将提出的方法应用于钢束有效应力预测,得到了跨中截面所有钢束的应力推定值。进行了桥梁极限承载力试验,得到全过程加载下的结构受力与变形实测值及破坏模式,并将理论算法与试验测试结果进行对比分析。研究结果表明:各级荷载下的试验梁应变理论计算值与试验测试值具有较好的一致性,提出的钢束应力预测方法和截面分析方法能准确反映开裂损伤预应力混凝土箱梁的力学特征,可用于开裂损伤的预应力混凝土箱梁桥运营期间承载能力的量化评估。

In order to perform quantitative assessment on the safety performance of PC box-girder bridges with cracks during service period,the evaluation method for the bearing capacity of a damaged PC box-girder bridge was carried out,based on the partial effective stress test of a tendon in PC box-girder bridge.Firstly,based on the principle of parameter identification and the correction method,the variation in transient prestress loss,including frictional loss and antifriction loss,was represented by the friction loss parameters,and a new method was proposed topredict the effective stress on the inner tendon from the outer tendon.Then,an equilibrium iteration algorithm and a procedure for considering the tensile strength of concrete in the cross section were developed.Finally,a full-scale experiment was carried out for three girders.The stress on the outer tendon at the mid-span section of the girder was measured using a special stress detector.Using the proposed method,the stress of the inner tendon at the mid-span section was predicted.The measured load,deformation,and the failure mode of the structure during the entire loading process was obtained.A comparison was made between the theoretical results proposed in this paper and the experimental results.The results show that calculated strain of the test girder is in good agreement with the experimental results,which illustrate that the stress prediction method of the tendon and equilibrium iteration method can accurately reflect the mechanical characteristics of a damaged PC box girder.It can be used to quantitatively evaluate the bearing capacity of box-girder bridges with damage during service period.3 tabs,9 figs,22 refs.