Study On Reasonable Section Design Of PC Simply Supported-Continuous T Girder

Elaborative investigation on the structural forms of certain inland bridges of simply-supported continuous illustrates that T girder, the single span between 30-60 meters, had been in the majority of the bridges constructed before the year 2014. However, deficiencies still consist in design and construction of prestressed concrete T girder. For example, there is larger reverse deflection error between girders hoisted in adjacent place; thin-web T girder often occurs lateral bending deformation during construction phase; cross connection of T girder contacts frequently with wheels because of improper arrangement of roadway; structure dimension of the same span bridge is not uniform, which leads to the result that formwork and construction equipment cannot be sufficiently recycled, and so on. Aiming at the deficiencies above, based on the project and construction of Baobei River Bridge in Inner Mongolia, reasonable section design of PC simply-supported continuous T girder was studied. Based on the characteristics of a PC simply-supported continuous T girder, the conception of reasonable design in relevant discipline and the problem existing presently in design and construction of T girder, the content of reasonable section design was drawn up. The content correlation between each other was discussed, and the methods of design and calculation of the detail were studied.The major research results as follows:(1) To avoid the most unfavorable position of bridge deck slab contacting frequently with wheels, a few of section arrangement were compared in order to select the relatively reasonable scheme. Relationships between slab moment and girder space, and the moment calculation formulas were gained by mean of curve-fitting method. According to the bridge specifications of China and referring to the bridge deck slab theory, the slab thickness is worked out, which contributed to the gaining of its change regularity under the conditions as rebar stress control, bending bearing capacity control and crack control. And the relationship between the slab span and optimum thickness was analyzed under the specific rebar layout. So the reinforcement layout and optimum slab thickness was attained under various slab spans. The design value of slab thickness is not only satisfied with the requirement of load bearing capacity under vehicle load, but also simplifies girder section optimization because of girder section variables reduced as a known value in girder section design.(2) By discussing on the general problem of section optimization design, the characters of variables, objective function, and constraint condition and optimization algorithm in bridge structure optimization design were concluded. The variables of the section optimization design were determined according to the structural feature of T girder. Constraint conditions of section optimization were established by the present bridge specification, however, requirements of construction deformation control that should be added into the conditions was put forward. The objective function of variable section prestressed concrete T girder with curved tendons was erected up. The characteristic and application of interior point algorithm, sequential quadratic programming method and active set algorithm was studied; algorithm selection problem was discussed. By utilizing MATLAB Optimization Toolbox, optimization tested calculation was carried out on the question of the existing reinforced concrete girders; comparisons were conducted to find out the features and efficiencies of different calculation ways to solve the problem of optimization of bridge sections. After testing and comparing analysis, interior point algorithm showed superior efficiency and effective when dealing with the optimum calculation of the reinforced concrete sections. The interior point algorithm was applied to optimization trial calculation for the existing PC girder, and the result showed it is the feasible optimization algorithm in PC section optimization design problem. Structural reliability problems are discussed, the relationship between the structure of cost and reliability, and the influence of related parameters was analyzed. A method for determining parameters as total investment being lowest was gained and evaluation criterion for optimization design based on reliability is given.(3) In order to study deformation of T girder in prestressing, the existing problems in calculation and control of T girder construction deformation were discussed, and the experiments of pre-stressed concrete T girder were carried out and the corresponding finite element model of ABAQUS was established. Further discussion was conducted about the frictional contact during the stretching process of the girder. Rules of the deflection change during the prestressing were revealed by finite element calculation. Further efforts were also made to propose the basic hypothesis of calculation. Force state of girder in construction was analyzed by means of a static method. The formula determining the boundary constraint conditions of reverse deformation and lateral bending deformation calculation was deduced. The design measure of construction deformation control was put forward considering the section optimization design.(4) The thesis carried out the reasonable section design for the Baobei River Bridge, established MIDAS infinite element model of the actual bridge by utilizing the performance of the experimental bridges. The design result was verified by the model. Comparison of the design results was conducted following the former design and the reasonable section design; the economic efficiency and bearing capacity evaluation was conducted. The results show:the amount of the prestressed reinforcement reduces; the girder height keeps same as the original; the width of web in span center remains the same; the width of web in support declines; the dead load of unit changes slightly; the cost of the girder unit drops; the average thickness of flangeslab increases; the amount of rebar in unit slab decreases. The difference of reverse deflection between boundary girder and center girder is smaller. The lateral bending deformation control is easy. The concrete quantities decrease; the quantities of prestressed reinforcement in girder and rebar in slab reduce. The cost of major engineering materials declines. The cost of three spans of superstructure is greater than it under objective reliability index design. As showed by the verification and analysis:the design result cannot only ensure the structure functional requirements, also make the structure meet the expectation and effect of the reasonable design.