非一致性收缩徐变对小箱梁桥腹板竖向开裂的影响

The influence of non-uniform shrinkage creep on vertical cracking of the web in a small box girder bridge

为分析某预应力混凝土小箱梁桥建成通车多年后,跨中腹板集中出现大量竖向裂缝的成因,研究采取封闭及梁底板预应力碳纤维板加固后裂缝依旧发展的机理,建立小箱梁桥截面分层模型,分别表征顶板、腹板、底板的物理力学行为,考虑因理论厚度及配筋率差异导致腹板处的混凝土收缩徐变比顶板及底板处大,推导小箱梁截面因非一致性收缩徐变产生自应力的计算方法。以实桥为算例验证此方法的有效性,计算得到腹板中部截面拉应力最大,截面拉应力沿顶板、底板方向衰减,与实桥裂缝形态一致;计算得到裂缝产生时刻与实际桥梁裂缝出现时刻基本吻合。研究表明:非一致性收缩徐变是导致小箱梁桥腹板竖向开裂的重要因素之一。

The study aims to analyze the causes of the vertical cracks concentrated at the mid-span web of a pre-stressed concrete box girder bridge,which has been in service for many years,and investigates the mechanismbehind the continued development of cracks even after the application of sealing and bottom slab reinforcement using carbon fiber sheets.A section-layered model of the box girder bridge is established to represent the physical and mechanical behaviors of the top slab,web,and bottom slab.The differential concrete shrinkage and creep between the web and the top/bottom slabs is taken into account which due to variations in theoretical thickness and reinforcement ratio.A calculation method is derived to estimate the self-induced stresses in the cross-section of the box girder bridge caused by non-uniform shrinkage and creep.The effectiveness of this method is validated by applying it to an actual bridge,which shows that the maximum tensile stress occurs in the mid-section of the web,and it attenuates along the top and bottom slabs,which is consistent with the observed crack pattern of the real bridge.The calculated timing of crack initiation aligns well with the actual occurrence of cracks in the bridge.The research demonstrates that non-uniform shrinkage and creep is important contributing factors to vertical cracking in the web of box girder bridges.