Behaviors Of Prestressed Concrete Box Girder For Partially Cable-stayed Bridges With Double Outwardly Inclined Cable Planes

Partially cable-stayed bridge, as an exemplification for combined bridges, become more striking and be recognized gradually by civil engineering for its design concept of "use cables to help the main girder". This bridge type is usually suitable for middle-span bridges and full of flexibility.Following the success of Fujian Zhangzhou Combat Readiness Bridge and Wuhu Changjiang Bridge, there have been dozens of such bridges in operation at home. Among them, the PC box girder with big width has gradually became the mainstream although its spatial mechanical properties have not been fully understood. Focusing on Chongqing Jiayue Bridge, which is a partially cable-stayed girder bridge with double outward-inclined cable planes, this dissertation deeply discussed many problems as following mainlined by preliminary design theories and special mechanical behaviors of the PC box girder with long-cantilever slab.1. Studies on the conceptual design and approximate calculation formulas.Based on the exiting research achievements on defining methods of partially cable-stayed girder bridge, and taking intrinsic character of "cable-stayed girder" bridge into account, this paper systematically expounds the determining principle of total design parameters and the key point of mechanical design of main beam. Furthermore, approximate formulas about internal forces of girder and cables under dead load and traffic load are deduced on the assumption of beam on elastic foundation.2. Studies on parametric behaviors of Partially Cable-stayed Girder Bridges based on trial designs in several kindsOn the basis of research results in the conceptual design stage, this paper carries on the analysis of the importance of parameters which affect the structural behavior of the partially cable-stayed girder bridge, and the coMParative analysis of several important structural parameters which affect the integral structural behavior of the partially cable-stayed girder bridge including the main stiffness, the length of no-cable girder, the initial cable tension, etc. According to the suggestion of this paper, the parameter optimization of partially cable-stayed girder bridge should take the requirement of different stages into account separately. Then this paper proposes a new optimal design method of variable stiffness (height) girder, and carries on a large amount of computational analysis about the iMPact on internal structural behavior caused by variable length of no-cable girder and variable initial cable tension. The research results play an important referential role to make sure the design key points of main girder and bring the superiority of partially cable-stayed girder bridge into further play.3. Study on the key problems of the PC box girder based on three dimensional analysisBackground of Chongqing Jiayue Bridge with double outward-inclined cable planes, this paper carries on the spatial structure simulation computes in all construction stages. Furthermore, to discusses the longitudinal and transverse deformation and stress distribution of flange-slab under the combined loads, especially the cable force with9800kN each. This paper also propose the reinforcement configuration method based on the stress of all construction stages which is the essential method to ensure the structural secure.4. Study on shear lag effect on the PC box-girder with big-width and long-cantilever slabThis paper coMPares the applicability of different researching methods on shear-lag effect for the PC box-girder with long-cantilever. Taking combined loads effect into account, including dead-weight, prestress, cable tension, the hanging basket, concrete shrinkage and creep, etc. this paper analyzes share lag effect on the roof in simulation cantilever construction processes of the girder, and indicates that share lag effect on area of the girder close to the tower in construction stage should not be ignored, although such effect would become weak in use stage.5. Study on single segment model test for the anchor structure of PC girderIn order to verify the concrete anchor region’s safety under9800kN cable force(that is each cable’s initial tension), a single girder segment trial model on1:3scales was carried out, First, according to the calculation results all of control points were decided; Then, to test the stress and deformation of such control points in scheduled gradating conditions; Furthermore, to coMPare the measured and the calculated values; Final, this paper suggests a reasonable improvement measure for the anchor region of the girder.6.Study on the cable tension optimal design of partially cable-stayed PC girder taking prestress effect into accountIn the paper, many optimization methods of cable force are systemically studied and summarized. Associated with the ideal final and construction stages used to be achieved by stressing all stay cables just one time, it is suggested that the forward cable-tension optimal method based on boosting prestress reinforcement efficiency of PC girder. Another suggestion was synthetically applying internal prestressing, external prestressing and cable force. Besides these, because of the girder’s stiffness, applying dilute cable system into the partially cable-stayed girder bridge. would be impossible.