Diagonal Cracks On The Bearing Capacity And Stiffness Of The Prestressed Concrete Box Girder Study

Pre-stressed concrete box girder are widely used in the engineering field , and will be widely used. But the problems about the cracks in the box girder webs of this bridge are becoming very boring difficulties to the engineering technicians in the present. Do the stiffness, the load carrying capability's changing rule and cracking situation satisfy the loading classes and actual request after the cracks in the box girder webs appear due to many factors, All of these questions has not been solved yet. In the paper, the finite element method is proposed on analyzing the stiffness and the loading capability which are influenced by the inclined cracks in webs. This method is based on the result of the cracks in the concrete study all over the world. And the analysis is done by this way to the concrete bridge.The thesis analyzes the mechanism, reason of the cracks creation and the classification of the cracks. The major point in the analysis is the reason of the inclined cracks creation in the box girder webs. All of this breaks through the importance in the study of the cracks. The author introduces the fundamental theory about the cracks' analysis and selects the rational reinforcing steel constitutive law and concrete constitutive law. During to the concrete destroy mechanism, the paper discusses the concrete destroy standard under the complicated stress situation. The calculation method is also introduced on the shear deformation and the shear load stiffness. The author analyzes the constitution of the bend's and shear's load carrying capability and the characteristic of the bend's and shear's parts. At last, the handling is discussed about the cracks.There are two finite element models established for the analysis on the load capability and the stiffness changes of the cracked pre-stressed concrete continuous box girder bridges: 3D solid model and 3D truss-beam model . The two methods' features and good scope are discussed and verified reasonable and feasible by a calculation example.Based on the real bridge's design data and the cracks statistics, the author can establish many calculation models by the mentioned two methods. The load carryingcapability and the stiffness changes, which are influenced by the inclined cracks' height and amount, can be analyzed. The paper evaluates the loading capability and the extant stiffness after the bridges crack. After the comparing the calculation results of these two methods, the author shows a conclusion that both the two ways can be used to analyze and evaluate the load carrying capability and the stiffness of the cracked bridges.