预应力混凝土连续箱梁施工质量评价指标调查

基于3座预应力混凝土连续箱梁桥的拆除工程，对预应力混凝土箱梁结构的预应力孔道灌浆饱满度、混凝土超方量及混凝土保护层厚度等施工质量评价指标进行了实地调查，并对实测指标进行了统计分析，揭示了预应力混凝土连续箱梁的施工质量现状。结果表明：中国预应力混凝土连续箱梁的总体混凝土超方率偏大，超方率一般在10％～20％，混凝土超方主要集中在箱梁顶板和底板；箱梁纵向预应力孔道灌浆不密实的比例超过50％，横向预应力孔道灌浆未达到密实状态的比例也超过70％，上述情况将使结构预应力损失增大；同时，截面混凝土超方及预应力损失增大将使预应力混凝土箱梁截面主拉应力增长明显，从而增大结构开裂的可能性；提出的量化分析指标有助于正确认识预应力混凝土箱梁桥上部结构普遍开裂和下挠过大的内在原因，为此类结构的研究提供了重要的依据。

Investigation of Construction Quality Evaluating Indices in PC Continuous Box-girder

Based on the dismantlement of three prestressed concrete （PC） continuous box-girder bridges, several construction quality evaluating indices for PC box-girder structure were investigated on the spot, which consisted of the duct grouting density degree of prestressing bars, concrete overweight percent and concrete protector thickness and so on, and then the indices were analyzed statistically to find out the current construction quality of PC continuous box-girder. The results indicate that the overweight ratio of PC continuous box girder in China is on the high level generally, it varies between 10%and 20%, and the performance of concrete overweight centres at top slab and low slab of box-girder generally. The duct area percentage of partial grouting for longitudinal prestressing bar is more than 50%, and the percentage for lateral prestressing bar duct grouting is more than 70%, but the performance of duct grouting being noncompacted in a large proportion make the prestressing loss increase obviously. In another side, the true calculating example in the paper indicates that concrete overweight and prestressing loss will enlarge the principal tension stress in PC box-girder, and make the possibility of structure cracking increase. The quantized surveyed indices proposed in the paper is helpful to realize the actual reason for cracking and big flexural down-warping of PC box-girder bridge, and also provide the important basis for structural analysis of PC box-girder.