Research On Cracks Along The Pipeline In Web Plate Of Prestressed Concrete Bridges And Prevention Measures

The cracks along the pipeline of web plate are very common in the diseases of prestressed concrete bridge. These cracks stretch along the pipeline from L/8 to 7L/8, and are about 0.1mm wide and reach corrugated pipe in the deepest position. The cracks along the pipeline of web plate could result in corrosion of ordinary steel and prestressed reinforcement, which is bad for carrying capacity, durability and beauty. However, specific measures and methods for this kind of crack have been not put forward in the design and construction. So this paper has detailedly carried on the cause of these cracks and has put forward relevant prevention measures.This paper, based on the current research status of the concrete cracks along pipeline, has discussed destruction mechanism of concrete and analysis method of using ANSYS for concrete bridge cracking analysis. According to the bridge design drawings, ANSYS finite element model has been established for cracking analysis of cracks along the pipeline. On this basis, the characteristics and distribution rule of the cracks along the pipeline has been obtained by investigation. In addition, the main factors of the web cracks along the pipeline has been preliminarily gotten from the perspective of theoretical analysis. After that, the reason for these cracks was explored respectively from the early stage of maintenance and the late stage of operations by using ANSYS finite element model, and what lead to these cracks has been proved to be the non-uniform shrinkage of concrete in the early pouring, the lateral deviation of pipeline and cross-section negative temperature gradient. At the same time, this paper has carried on the quantitative analysis for adverse effects of lateral deviation, and has dissected the coupling effects of the above three factors. It turned out that it is easy to produce cracks along the pipeline, when considering coupling effect of non-uniform shrinkage and pipe deviation as well as coupling effect of cross-section negative temperature gradient and pipe deviation.Secondly, on the basis of the above factors analysis, this paper has particularly studied how web thickness and stirrup affect cracks along pipeline from the aspects of design. In accordance with research results, the larger shrinkage strain in the early days would lead to an increase of principal tensile stress under the effect of stirrup. If shrinkage strain can be decreased, stirrup will play a significant role in reducing the principal tensile stress of concrete along the pipeline of web plate and limiting crack developing. In the same way, if shrinkage strain can be diminished, appropriately increasing the thickness of the web also can significantly reduce principal tensile stress of concrete along the pipeline of web plate.Finally, the prevention and control measures are put forward respectively from the two aspects of design theory and construction technology. Namely, in the process of construction and maintenance, it is significative to take some appropriate measures to reduce the non-uniform shrinkage strain of the web plate and transverse deviation of the corrugated pipe. Meanwhile, in the aspect of design, it is effective to increase the thickness of the web and arrange the stirrups along the pipeline. Besides, this paper also puts forward the repairing and strengthening proposal for the cracks along pipeline of built bridges.