The Research On The Influence Of The Inner Inforce Of The Box Girder For The Pre-stressed Strand Arrangements

In recent two or three decade years, the large-span PC box girder bridges have been widely used, and will be more widely used. But quite amount of cracks are found during the construction and operation in the PC box girder bridges, especially cracks in the anchorage zone and the inclined cracks in the box girder webs of the bridges, and some longitudinal cracks appear indeed in the deadweight phases,Moreover the variant Pre-stressed strand arrangements produce great influence for the inner inforce of the box girder. Therefore this paper analyses the great influence of the inner inforce of the box girder for the variant Pre-stressed strand arrangements by using great Finite-Element . This thesis discusses the suffering characteristic and analysis method on box-section in detail. It analyzes the stress state of the box girder webs. The paper takes Dongjiang Fourth Bridge in Huizhou city as an example for searching for the influence of Pre-stressed strand arrangement on the craze of box girder. By using great Finite-Element analysis ANSYS special part model of box girder have been built up through adopting three-dimensional body element. In order to considering the affection of the axilla of peduncle in top,bottom slab, it actually simulates three-dimensional trait of the segment and does not predigest the section lest the calculation of the model should not accord with the fact. The analysis result of the shaft system applies on part model by the way of boundary condition of part model, and three-dimensional pre-stressing tendons are considered as a single element.Longitudinal pre-stressing tendons is considered according to three different ways which are the designed pre-stressing tendons,straight pre-stressing tendons and bend pre-stressing tendons ,vertical pre-stressing force is applied to according to second different ways which are the designed pre-stressing tendons and one half designed pre-stressing tendons, analyzes the three-dimensional stress of part model in maximal cantilever state, dead and live load state, especially on the region of box girder webs,the upper plate and the anchorage concrete zone. Through calculated result analysis,Finite-Element analysis on three-dimensional part model is necessary and valid, the number of vertical pre-stressing forces and the variant longitudinal Pre-stressed strand arrangements for diagonal tension stress of the web in diagonal tension stress of the box girder webs has important influences by accounting for reasonable pre-stressed strand arrangement and valid pre-stressed force to improve. In addition, moreover the Pre-stressed strands which are anchoraged in the box girder webs produce great influence on the anchorage concrete zone,and the variant longitudinal Pre-stressed strand arrangements produce great influence of the inner inforce of the box girder upper plate,so it is paid attention to in design through collocating a number of common reinforcing steel bar.