The Application Research Of Unstressed State Control Method For Bridges Constructed In Stages

Unstressed State Control Method is a kind of theory,which is used to solve the structural calculation problem of bridges constructed in stages. It established a mechanics equilibrium equation of bridges constructed in stages for the first time in the world,the equation for the first time illustrates theoretically that the unstressed state amount is the nature factors that influence the resistance and displacement of bridges constructed in Stages.Thus,the unstressed state amount of building blocks can be used to control the resistance and displacement of bridges constructed in stages and the final state.Currently, Unstressed State Control Method has formed a set of theories and methods of the system. But with the development of bridge structure in large span, especially for cable-stayed bridge,the stiffening girder generally uses the form of steel box girder,the ratio of beam height and span further reduces, the proportion of the main girder becomes more slender, In view of this,the geometric nonlinear problem of structure system becomes more prominent. In order to use Unstressed State Control Method in the calculation of long-span cable-stayed bridge’s construction stage, this paper research content is as follows:1.The basic equation for Unstressed State Control Method.The energy method is used to set up the general mechanical equilibrium equations of Unstressed State Control Method for structures constructed in stages,when the geometric nonlinearity effect is considered. According to the general mechanical equilibrium equation,the mechanical equilibrium equations for Unstressed State Control Method of the plane beam element structures and plane bar element structures is obtained.Finally,based on analytic theory,the mechanical equilibrium equations for Unstressed State Control Method of flat cable tensioned in stages is concluded.Finally,the problem of the nonlinear solution of the mechanical equilibrium equations for Unstressed State Control Method of flat cable tensioned in stages is presented.2.According to the nonlinear finite element theory,the total formulation and incremental formulation of the equations equilibrium equations for Unstressed State Control Method of plane beam element structure is obtained;the process of using the TL formulation, UL formulation, CR-UL formulation, CR-TL formulation to solve the equilibrium equation is discussed in detail.The superiority of using the corotation coordinates to solve the geometric nonlinear problem is proved by an example. The basic thought of solving the equilibrium equations by using the above four formulations, is also applicable for bar element and cable element.3.The general mechanical equilibrium equations of Unstressed State Control Method for structures constructed in Stages is proved by an example.The essential reason which Resistance and displacement of a one-time forming structures and structures constructed in stages is different, is not because the different forming way but the different unstressed state amount.4.The application of Unstressed State Control Method on cable-stayed bridge construction simulation calculation is carried on the theoretical analysis, then the basic principles of un-stress forward-calculation are expounded.With two cable-stayed bridge projects as an example, To a level 500 m cable-stayed bridge, the result by using unstress forward-calculation is the same as the reasonable completed bridge state,and this method is more simple than the combination iterative analysis of forward-calculation and back-calculation.To a level 600 m cable-stayed bridge built respectively in two different forming ways, one-time tension cable force of two different forming ways is different,which is calculated by unstress forward-calculation method, but the variation trend of the cable force is roughly the same, and the final cable force is converged to a reasonable completed bridge state, And resistance and displacement calculation result of final state of grider is slightly different with reasonable bridge state.The above results show that Unstressed State Control Method is reliable in construction simulation calculation of the large span cable-stayed bridge.By this,the basic equation for Unstressed State Control Method is verified further.In this paper, the calculation result provides a theoretical basis and reference for the promotion of unstress forward-calculation.