Identification, Cause Analysis And Reinforcement Of Cracks In Box Girder Web

Prestressed concrete box girders have been rapidly developed and widely used in modern transportation construction because of their light weight and high torsional strength,but many domestic prestressed concrete box girders in service have various types of cracks,especially cracks in the web of box girders are more common,which affect the bridge performance and durability.Therefore,this paper investigates the mechanism of vertical cracks in the web of prestressed concrete box girders,and then provides ideas for the prevention and reinforcement measures of vertical cracks in the web of box girders,and the main research contents and results are as follows:(1)Based on the types of bridge cracks measured in the field,a lightweight Bise Net V2 semantic segmentation model is established to identify cracks in bridge webs,and the trained semantic segmentation model achieves a cross-comparison ratio of 0.93;a machine vision architecture based on deep learning and traditional graphics is established to obtain the length and area of cracks,and the canny detection results optimized by the semantic segmentation model are compared with the Gaussian filtered results.The semantic segmentation model is found to be able to reject the noise well.(2)Midas/Civil and Midas/Fea were used to establish the overall and local finite element models of the dependent project to analyze the causes of vertical cracks in the web of the box girder.The main conclusions: the normal use stage cracking test and the lasting condition stress test were carried out for each main control section in the construction stage,and all the requirements in the design stage met the code requirements;for the influence of the construction stage on the vertical cracks of the web,the temperature effect of heat of hydration and sudden cooling was simulated by setting the temperature difference between the inner and outer layers of the web concrete,and the heat of hydration and sudden cooling in the construction stage were found to be the causes of the vertical cracks in the web of the box girder.For the effect of vertical cracks in the web during the operation stage,we analyzed the vertical temperature difference in the web and the deterioration of concrete material,and found that the vertical temperature difference in the web had the greatest effect on the first principal stress in the web,and the material deterioration increased the first principal stress in the web on the one hand,and reduced the tensile strength of concrete on the other hand,which led to the deterioration of the cracking condition.(3)Through the professional sunshine analysis software to calculate the sunshine duration of the box girder web,to obtain the temperature distribution of the box girder web.It is found that there are temperature differences in different locations of box girder web due to the difference of sunshine time,and the temperature distribution varies with latitude and trend.For northeast southwest box girder bridge,especially in the high latitude area,the temperature stress generated by the influence of sunshine duration on the web is large,which is easy to lead to cracking.Due to the vastness of Chinese highway regulation set by our country for temperature field may be unsafe in some regions.Concrete project needs concrete analysis.(4)The feasibility of reinforcing the vertical cracks of web by spraying high-performance concrete is discussed from the point of stress.The influence of different thickness and elastic modulus of high-performance concrete on the first principal stress of web is analyzed.The results showed that the first principal stress of the web decreased with the increase of the reinforcement thickness and increased with the increase of the modulus of elasticity.The results show that the first principal stress in the web decreases with increasing reinforcement thickness and increases with increasing modulus of elasticity,and the functional relationship between the first principal stress and reinforcement thickness and modulus of elasticity is found by multiple linear regression to provide a calculation for future reinforcement projects.