Research On Control Theory And Application Of Structure Formed In Stages

Staged construction structure represents future direction of bridge engineering,and its completion state includes the structural internal force state and geometric shape state.Structural analysis and construction control of staged construction process is an important issue for modern long-span bridges,and staged construction theory is a major tool to solve confronting problem for the long-span bridge analysis and construction control.The core of this theory is consisted of mechanical equilibrium equations and geometric shape governing equations for staged construction structures,and three basic principles were proposed based on the above two types of equations.This thesis focuses on the mechanical behavior of the staged construction structure.The two types of governing equations which are mechanical equilibrium equations and geometric shape governing equations were summarized for staged construction structure under geometric linear condition.Secondly,the above two types of governing equations were further derived for the one-dimension element considering the geometric nonlinear condition and validated by several examples.The corresponding finite element(FE)analysis program was developed as well.It has been demonstrated that three basic principles in stress-free-state method are still correct even if the structural geometric nonlinear effects are considered.Finally,the stress-free state theory was validated by three existed practical engineering cases considering the structural geometric nonlinear effects,and it was extended to the bridge structure closure,the stress-free geometric shape determination of structural elements and the internal force optimization of steel truss girder.The major works in this thesis are as follows:1.The basic stress-free-state variables which are stress-free length,stress-free curvature and stress-free angle for one-dimension elements were defined.The stress-free geometric shapes for segment element of steel box girder and bar element of steel truss girder were related to the these above three stress-free-state variables.Based on the element stress-free state,staged construction characteristics of one-dimension bar element,two-dimension beam element and three-dimension beam element were investigated by minimum potential energy theorem and element stress-free-state variables,which the geometric nonlinear effect was considered.The staged construction mechanical equilibrium equations were derived for these above several elements.It can be concluded that the stress-free state theory principle 1 and 2 are still valid even considering the structural geometric nonlinear effect.That means that when the stress-freestate variable of a structural element including geometric nonlinear effect is set,the initial force and deformation of the nonlinear element are unique at the completion state of the structure regardless of its construction process.These two conclusions provide theoretical basis for the staged construction structure considering geometric nonlinearity.The developed FE program took the stress-free-state variables as input parameters and five sorts of examples were utilized to validate both the theory and FE program.2.Two structural system states and three element states were defined.Based on the element stress-free state,staged-construction processes of one-dimension bar element and twodimension beam element were investigated by minimum potential energy theorem and stressfree-state variables,which the geometric nonlinear effect was considered.The staged construction geometric shape governing equations were derived for these above two elements.Several insights can be obtained by analyzing these equations:(1)It is difficult to get the stressfree-state variables directly since the geometric governing matrix and structure stiffness matrix both include the rotation angle variable θ.(2)The nonlinear geometric shape governing equations degenerates to linear equations and the rotation angle θ equals to zero in the final equilibrium state.(3)The stress-free-state variables are unique for statically determinate structure since the internal force balanced with corresponding external force is also unique.While for the statically indeterminate structure,there are an infinite number of solutions for the structural components internal forces corresponding to unique external load.Therefore,the stress-free-state variables also have an infinite number of solutions.The conclusion can be derived that the internal force is independent of geometric shape by control the structural stressfree-state variables actively,and it was validated by the calculation example.The relation and difference were discussed between mechanical equilibrium equations and geometric shape governing equation of staged construction structure.3.The stress-free state theory was validated by three existed practical engineering cases considering the structural geometric nonlinear effect.(1)The analysis theory of cable-stayed bridge construction.Firstly,a nonlinear cable force optimization algorithm was proposed to adjust the tensile force of cable for the rational completion state establishment of cable-stayed bridge,which assumed that each cable was independent with the others.Geometric nonlinear effect was excluded by applying initial tensile force on the cables.The optimal numerical solution was derived according to constraint condition and objective optimization function.Moreover,both the stress-free-state method and backward analysis method were employed to establish the construction state of cable-stayed bridge.The results demonstrate that the construction states through both methods are the same,and the stress-free-state method can be used to determine the intermediate construction state of structure with geometric nonlinear effect.The stress-free-state method can link the objective completion state and construction state with the employment of stress-free variables of structural components directly,and the rational construction state can be derived subsequently.The calculation problem can be solved successfully combining the novel tensile force adjusting method and stress-free-state method.(2)The filtering of temperature and temporary load effect.A novel thought was proposed that the tensile force was controlled by the tensile length of cable.It was proved that controlling the tensile length of cable can effectively filter the unfavorable effect of temperature and temporary load based on theoretical and mechanical models,and a calculation example was taken to validate this approach.(3)The parallel construction operations.The reliability of parallel construction operations in bridge engineering was discussed based on the mechanical equilibrium equations.The reliability of parallel construction operations was validated by two examples as well.The 1st example is the parallel operation of tensile force adjustment and crane forward,and the 2nd one is the parallel operation of tensile force adjustment within wide range and secondary dead load application.4.The application of stress-free state theory was expanded.(1)The closure technique in bridge construction.A closure concept with stress-free geometric shape was proposed in bridge construction.The completion stage of bridge is independent of bridge closure techniques only if the stress-free-state variables of structural components keep constant.The stress-free geometric shape error adjustment method of bridge segment was put forward.The completion state of structure is not sensitive to the distribution of the accumulated error of stress-free-state variables if all accumulated errors were corrected in the final segment.The stress-free state of girder in practice is the same as the objective stress-free state under this condition and the automatic approximation of the objective value in the bridge completion state is realized.(2)The determination of stress-free geometric shape of structural elements.The calculation method of stress-free geometric shape for one-dimension element was proposed according to geometric shape governing equations.Taking the steel truss girder as an example,the structure can achieve the state that it has the same geometric shape while different internal force state.The stress-freestate method and the linear superposition method were compared by taking the steel box girder as an example.The results demonstrated that(1)As the structure presents significant geometric nonlinearity,the bridge geometric shape and internal force in the actual completion state would obviously deviate from the ones in its target completion state if the linear superposition method is used,which especially reflects in the mileage error.(2)Compared with the linear superposition method,more precise and rational stress-free geometric shape for the bridge segment can be obtained by stress-free-state method,which is independent from the geometric nonlinearity.(3)The optimum internal force state of steel truss structure.According to the geometric shape governing equation,an optimum approach was proposed for improving the internal force distribution of steel truss components.The optimum internal force state was obtained by releasing the secondary moment of joints in the web components firstly.Then the stress-free variables of components can be obtained according to the optimum internal force state and structure geometric shape in completion stage.The stress-free-state method had been validated by the examples that it was good at improving the internal force state of web component in steel truss girder and reduce the dimension of cross section.