Research On The New Type Web Structure Of Long-span Prestressed Concrete Continuous Rigid-frame Bridge

Prestressed concrete (PC) continuous rigid-framed bridge has the advantages of big bending stiffness along vertical bridge direction and the torsional stiffness along the horizontal Bridge direction , good seismic performance and traffic smoothly. Additionally, It has simple constructruction and low maintenance cost. So it was relatively rapid developed in the past 40 years. The span has been developed from about 100m to over 300m around the world. PC continuous rigid-framed bridge has become one kind of the long-span bridge structure in the Gulf, the ravine,and large river. In the other hand, with PC continuous box girder bridge was used widely,diseases reports on this type of bridge become more and more. The highlighting problem is principal tensile stress leading to cracks in web which can affect the structure work normally and durability,it occurred mainly in cast-in-place segments of side span, segments around L/4 main span and thickness changing of web;Long-term deformation of main span is bigger than the design value.This paper focuses on the following four aspects in light of the problems:1,The project of Sha-xi-gou bridge Ju Yun avenue in Fu Ling district was taked as background. By using the finite element software as simulating computate method, the lessening of longitudinal pre-stress in top and bottom plate, which will effect the long-term deflection at key sections, such as, the section of 0# segment, L/4 segment and middle span, were analyzed. The analysis results indicate that one of the main reasons is the lessening of longitudinal pre-stress leading to the downwarping continuously.2,Taking the project of Da-du river bridge in Han Yuan as background,the bending continuous external prestressed wires were used to control the long-term deflection. Simulation results show that the external prestressed wires can improve midspan deflection directly. Additionally, they can improves stress states of top and bottom plate and web in key segments of main span effectivly,increases the safety degree of normal stress of entire bridge and inhibits the forming of cracks,slows down or stops the concrete cracking.3,The expansion rate determination of grouting material under the different allocated proportion is carried on through the material test in view of the web concrete cracking of pre-cast T Beams of Sha-xi-gou bridge in east and west avenue of Fu Ling district. The expansion of grouting material acting as the concrete around passageway was analyzed by the finite element software. The calculational results indicated that the stress produced by expansion of grouting material has surpassed the concrete limit tensile stress, and it will cause the web concrete cracking.4,According to concrete strut-and-tie model theory,truss stiffed skeleton was used at segments around L/4 span and midspan in continuous rigid-framed bridge. The analyzed results of this new type web show that truss stiff skeleton can improve principal tensile stress states effectively,and increasing safety degree of the principal tensile stress of bridge. Concrete cracking will be inhibited. Additionally, setting prestressed truss stiffed skeleton can reduce midspan deflection and inhance the loading capacity effectively...