Failure Test Of Prestressed Concrete Box Girder And The Influence Of Initial Imperfection

Prestressed concrete box girder is widely used in highway and municipal bridges due to its unique advantages.However,since the construction quality in early stage cannot meet the requirements and later operation management is not in place that initial defects and cracks in the box girder are generated.Not only the performance of bridge structure is effected,but also the safety of the structure can be endangered.Therefore,it is necessary to research the whole loading process of the box girder and analyze its mechanical performance affected by initial defects and cracks.This paper is divided into two parts.In the first part,a destruction test has been conducted on a north-south 30 m prestressed box girder in XiangYang.The overall mechanical response of the girder is studyed and the the relationship between the crack and capacity is evaluated based on the data of measured crack.In the second part,the concrete floor defect,webs of concrete defects,Inflation and core mold floating,four kinds of actual construction defects are simulated through numerical methods.Numerical simulation results of various types of construction defects and defect-free beams were compared to study the influence of bearing capacity subjected to different defects.The main results of this study are the following aspects:1.In this paper,finite element numerical simulation and field test are combined to study the mechanical properties of a 30 m prestressed concrete box girder.The simulation results agree well with the experimental results.Therefore,the reliability of the field test data and the effectiveness of ultimate bearing capacity calculated by finite element model have aslo been verified.2.According to field data and finite element simulation results,the stiffness degradation law of test beam are studyed.Then the stiffness degradation law along with the beam deformation are obtained through MATLAB curve fitting the data.3.The development law of crack has also been obtained based on filed data: 1)Both crack width and height grow under a increasing load,but with the load increasing to a certain extent,only the growth of crack width are shown;2)The decreasing trend of crack height and width from midspan to both sides are represented;3)The average distance between cracks decreases with increasing load.A sharp increase in the number of cracks along with a rapid decrease in the distance appear on the emeging stage of cracks.However,as the load continues to increase,the number and the average distance of cracks trends to be stable.4.Relationships between average crack width and the deflection of midspan section deflection,stiffness and loading rates are obtained based on regression analysis of the measured data.Thus,a rapid assessment of the stress state of the girder is conducted,and then the residual bearing capacity of the girder can be obtained.5.With a prestressed concrete box simply supported girder bridge for study,the influence of defects on the mechanical properties of the girder is investigated,considering four common defects of prestressed box girder in the construction process:sectional loss on the soffit(SLS),sectional loss on the web(SLW),excessive concrete on the soffit(ECS)and vertical deviation of inner mold(VDIM),which are simulated by ANASYS.6.Through numerical analysis and comparison between non-destructive girder and defect girder,various types of construction defects are proved to have no significant effect on the ultimate bearing capacity of the girder while there are varying degrees of influence on cracking,deflection and stiffness.Concrete floor defect has a greater effect on stiffness.