Study On The Capability Against Cracking Of The Pre-stressed Concrete Box Girder Bridges From The Design Aspect

Aiming at the crack phenomena in long-span prestressed concrete continuous box girder bridges at present, on the background of four differet span bridges, the main factors effectting the capability against cracking for long-span PC box girder bridges are studied and discussed in this thesis. The main contents are described as follows:Through looking over lots of literatures, the standpoint is brought forward in this thesis that the key on analysis of the capability against cracking for long-span PC box girder bridges is three-dimensional stress, especially the the local analysis. Both of the material performance and the characteristics of box girder are considered to confirm the determinant rule of cracking. This is also the basis of simulation of the structures.Incorporated with the three-dimensional analysis of continuous bridges, the temperature difference, prestress loss, deflection and live load are studied to compare their influences on stressing state. And the conclusion is considered to be that prestress loss is the main factor for three-dimensional stress, then the local temperature difference.On the reaserch of the whole model, the local area where nearly cracking happens is analyzed. The form and trend of cracking is also be forecasted.Through FE analysis of local area for four continous box girder bridges, the necessity of three dimensional analysis of prestress effects is proved. Suggestions for reasonable status of prestress in box girder are proposed. The form and trend of cracking is also be put forward on the basis of local stress analysis, and the areas where need to be strengthened are also confirmed.