Analytical Theory And Method Of Bridges By Two-dimensional Staged Construction

Bridges by two-dimensional staged construction are segmentally constructed both along axial direction and on cross section, which leads to great difficulty both in construction and analysis. In this thesis computational theories and approaches are studied via theoretical derivation and numerical programming based on the present theories of bridges erected by stages with one-dimension as follow:1. Calculation method based on unstressed state amounts was developed on frame structure by staged construction. The unstressed state amounts were defined and structural equilibrium equation by staged construction was derived on Timoshenko beam with constant (variable) cross section. The effect of lateral load on beam element was studied.It was suggestive that the fixed-end reactions generated from lateral loads were not negligible in determination of unstressed state amounts.2. Calculation method based on unstressed state amounts was established on shell structure formed by staged construction. The shell element was considered as a combination of plane stress element and thin bending plate element based on Kirchchoff assumption. Displacement mode was studied to derive the unstressed state amounts of various element types including triangle plane stress element, quadrilateral isoparametric conforming and nonconforming elements, triangular and quadrilateral isoparametric thin plate elements. The corresponding equilibrium equations were derived using the principle of minimum potential energy.3. The effect of temperature difference between construction and designed condition was studied on the elemental unstressed state. Based on uniform and gradient temperature modes, the effect of temperature difference was derived on Timoshenko beam with variable cross section. It was found that the uniform change of temperature in beam element was equivalent to the change in unstressed length while the gradient temperature change equivalent to unstressed state amounts change of both length and curvature. For shell element, similarly, the uniform temperature change was equivalent to the change in unstressed state of plane stress element while the gradient temperature change equivalent to unstressed state amounts change of both plane stress and bending plate elements.Consequently the temperature effect could be solved by substituting the revised unstressed state amounts into equilibrium equation.4. Computational programming was performed on bridge by two-dimensional staged construction and used for the verification of theoretical derivation. With the assistance of object-oriented C++ and OpenGL three-dimensional display system, the two-dimensional staged construction analysis programming was built. The program was applied to verify the staged construction equilibrium equation on Timoshenko beam (both constant and variable section) and plane shell element. Computational analysis was further conducted to verify the theoretical derivation on beam-shell connection, lateral loading and temperature effect. The results showed that the theoretical derivation and program are correct.5. The program of two-dimensional staged construction was applied on a major railway bridge to evaluate construction temperature effect on deflection and stress of final structural state. Numerical analysis results showed that the difference between in-situ construction and designed temperature was significant and the stress was not ignorable in bridges by two-dimensional staged construction. The random error effect of construction temperature was also studied on final stress and deflection of bridges by two-dimensional staged construction. It showed that stress was sensitive to temperature error.Calculation theories and methods of bridges by two-dimensional staged construction were fully studied in this thesis through theoretical derivation and computational programming. The conclusions provide theoretical methodologies as well as technical reference for design and construction of bridges by two-dimensional staged construction.