Research On Cracking Behavior Analysis And Reinforcement Of Prestressed Concrete Box Girder Bridge

Prestressed concrete box girder bridge which has many advantages has already been widely applied in highway and municipal road, however various reasons, such as early incomplete design, poor construction quality and lower load grade, lead to formation of crack in the top plate, bottom plate, web and other parts of many box girder, which have negative effect on stiffness, carrying capacity and durability of bridges. It is theoretical value and guiding significance in engineering that to analysis reasons of crack formation and their influence to structure, and to propose effective reinforcement methods.This paper establishes space finite element model considering three-dimensional prestress based on existing research achievement of crack of a certain prestressed concrete box girder bridge and carries on static analysis of the model to analyses the reasons of crack and their effect to structure. The results show that large number of cracks appeared in web are mainly due to vertical tendons prestress loss in construction state and gravity load, gradient temperature load and vehicle load result in the distribution difference of web crack (there are more cracks occurred inside of web than outside); Longitudinal cracks of top plate are mainly caused by gradient temperature load and vehicle load; Longitudinal cracks of bottom plate and"å…«"character-type cracks in anchorage zone are mainly caused by closure prestressing tendons of middle span and side span, vehicle load also speed up the development of these cracks. The length, depth and quantity of longitudinal cracks of top plate and bottom plate have influence on structural stress and deflection, but the influence degree is low and the influence degree of bottom plate is bigger than top plate's.In addition, this paper also discusses the application of external prestressing reinforcement technique in bridge reinforcement. Numerical analysis shows that external prestressing can greatly enhance transverse compressive stress of top plate, bottom plate and vertical compressive stress of web, thus cracks of those parts are prevented to develope and re-generate.Finally, the study analyses dynamic characteristics of the bridge combinating with dynamic load test, results also show that the cracks have little influence on structural stiffness although massive cracks occurred in top plate, bottom plate and web of the bridge.