基于钢筋锈蚀的PC等截面箱梁桥底板开裂研究

发布时间：2018-05-26 13:39

本文选题：PC等截面箱梁桥 + 钢筋锈蚀　；参考：《长安大学》2015年硕士论文

【摘要】：钢筋锈蚀引起的混凝土开裂是造成钢筋混凝土桥梁结构耐久性失效的重要原因,尤其是滨海环境中底板钢筋较多的PC等截面箱梁桥,因外界环境中氯离子浓度较高,干湿交替环境明显,极易引起混凝土内部钢筋锈蚀,造成底板锈胀开裂。而且国内外关于混凝土锈胀开裂的研究主要是针对普通钢筋混凝土构件,对于考虑桥梁运营中荷载作用的混凝土锈胀开裂研究很少,所以研究考虑桥梁运营中荷载作用的混凝土锈胀开裂意义重大。本文以福建某PC等截面箱梁桥为依托,着重研究裂缝调研中发现最多的底板纵向锈胀开裂。1、理论分析钢筋锈蚀引起混凝土开裂的机理,在假定PC等截面箱梁桥底板钢筋均匀锈蚀的前提下,推导钢筋锈蚀后引起的混凝土径向位移(锈胀位移)与钢筋锈蚀率的关系。2、利用Midas Civil建立某PC等截面箱梁桥正常状态下的整体有限元模型,分析在正常施工及运营过程中不同荷载组合作用下箱梁正截面最大应力状态,并在此基础上对正截面受力最不利且纵向裂缝发生较多的梁段建立Ansys局部模型,分析该部分梁体底板横向应力及主拉应力状态,得知在正常施工及运营过程中底板不产生结构受力裂缝,验证了本文重点分析钢筋锈蚀引起PC等截面箱梁桥底板开裂的正确性。3、在正常状态下有限元分析的基础上,研究PC等截面箱梁桥底板纵向钢筋锈蚀后底板混凝土应力分布规律、开裂过程及不同开裂阶段所需径向位移和锈蚀率。(1)PC等截面箱梁桥底板纵向钢筋锈蚀后,引起底板混凝土应力增大,最先造成钢筋周围混凝土初始开裂。随着钢筋的不断锈蚀,底板外侧混凝土出现可见裂缝,钢筋继续锈蚀,内部裂缝向外扩展,外部裂缝向内扩展,最后裂缝沿着锈蚀钢筋垂直或斜向贯通整个底板混凝土保护层。(2)角区及单根钢筋锈蚀引起底板可见锈胀裂缝时所需径向位移和锈蚀率更小,更易造成底板纵向可见锈胀开裂。(3)角区及多根钢筋锈蚀时对桥梁结构损伤更为严重,可能会造成底板混凝土保护层整块或整体脱落。4、相同外界条件下,考虑运营中荷载组合作用的PC等截面箱梁桥更容易产生底板可见纵向锈胀裂缝,建议从材料、设计、施工和管养四个方面采取相关措施进行控制。
[Abstract]:Concrete cracking caused by steel corrosion is an important reason for durability failure of reinforced concrete bridge structure, especially for PC equal-section box girder bridge with more reinforcement on bottom slab in coastal environment, because of the high concentration of chlorine ion in the outside environment. The dry-wet alternating environment is obvious, it is easy to cause the internal reinforcement corrosion of concrete and cause the bottom plate to rust and crack. Moreover, the research on concrete rust expansion cracking at home and abroad is mainly aimed at the ordinary reinforced concrete members, but there is little research on the concrete rust expansion cracking which takes account of the load in the operation of bridges. Therefore, it is of great significance to study the corrosion cracking of concrete considering the load in bridge operation. Based on a PC equal-section box girder bridge in Fujian Province, this paper focuses on the longitudinal corrosion cracking of bottom slab found in the investigation of cracks, and theoretically analyzes the mechanism of concrete cracking caused by reinforcement corrosion. Under the assumption that the steel bar of PC equal-section box girder bridge is uniformly corroded, The relationship between the radial displacement (corrosion displacement) of concrete and the corrosion rate of steel bar caused by steel corrosion is derived. The integral finite element model of a PC box girder bridge under normal condition is established by using Midas Civil. The maximum stress state of normal section of box girder under different load combinations during normal construction and operation is analyzed. On the basis of this, the Ansys local model is established for the beam segment with the most unfavorable force on normal section and more longitudinal cracks. By analyzing the transverse stress and the main tensile stress state of the bottom slab of the beam body, it is known that there is no structural stress crack in the normal construction and operation process of the bottom slab. In this paper, the correctness of the cracking of PC box girder bridge caused by steel corrosion is verified. On the basis of the finite element analysis under normal condition, the stress distribution law of the bottom slab concrete after the corrosion of steel bar in the bottom plate of PC equal-section box girder bridge is studied. The radial displacement and corrosion rate required in different cracking stages of box girder bridges with different cracking stages are followed by the corrosion of longitudinal steel bars on the bottom slab of box girder bridges with the same section, which results in the increase of concrete stress in the bottom slab and the initial cracking of the concrete around the reinforcement. With the continuous corrosion of steel bars, cracks appear on the outside of the floor concrete, and the steel bars continue to corrode, the internal cracks extend outward, and the external cracks expand inward. Finally, the radial displacement and corrosion rate are smaller when the cracks are perpendicular or oblique along the vertical or oblique direction of the corroded steel bar through the whole bottom concrete protective layer, and the radial displacement and corrosion rate are smaller when the corrosion of the steel bar causes the corrosion crack of the bottom plate. It is more likely to cause more serious damage to the bridge structure in the longitudinal corrosion zone of the bottom plate and the corrosion of several reinforcing bars, which may result in the whole or integral shedding of the concrete protective layer of the bottom slab, under the same external conditions, Considering the load combination in operation, PC equal-section box girder bridge is more likely to produce longitudinal rust expansion cracks on the bottom plate. It is suggested that relevant measures should be taken from four aspects: material, design, construction and maintenance.
【学位授予单位】：长安大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：U441.4

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