Theory And Application Of Unstressed State Method:

Cable-stayed bridge is one of the most widely-used types of modern bridges. The final structural state is directly affected by construction stages, because of high statically indeterminate and obvious3D effect. Thus it is vitally important to determine the reasonable state of construction stages. In my study the applications of Unstressed State Control Method are researched in bridge construction control and other relative fields. The dissertation is divided into four parts below according to its structure and content:Part I:The objective, content and methodology of construction control for cable-stayed bridges are introduced in this part. Then the calculation method of reasonable state of construction stages and final structure is summarized. A simple example is used to illustrate the inverted-disassemble method. The calculation shows that disregarding time-dependent effect of materials, the closing of inverted-disassemble and assemble calculation could be realized if only reasonable inverted-disassemble conditions have been achieved. Finally the no-closure phenomenon of traditional calculation methods is summarized and explained.Part Ⅱ:Based on the minimum potential principle and the characteristics of bridge constructed by stages, the equilibrium equations for geometry linearity (plane and space beam element) and nonlinearity are established. The Theory of Unstressed State Control Method and the definition of elements’unstressed state are explained in detail based on two kinds of common misunderstandings for element unstressed curvature. Finally the reliability of Unstressed State Control Method is verified in cable-stayed bridge ignoring time-dependent effect of concrete.Part III:The application of Unstressed State Control Method on the calculation of construction stages for concrete cable-stayed bridges is explained in detail and the reason of convergence is researched. According to the differences between cable forces at final state of assemble calculation and the objective state, revised formula of unstressed cable length with convergence acceleration is derived. Then the calculation of reasonable construction stages by method of inverted-disassemble and assemble iteration is explained and compared to the Theory of Unstressed State Control Method. The convergence nature of these two methods is studied in this part.Part IV:The applications of Unstressed State Control Method in other engineering applications are introduced in this part. In the case of Erqi Yangtze River Bridge at Wuhan, the applications on construction of bridge deck, parallel operation of crane moving and cable adjusting and the large overall adjusting of cable forces are introduced. The feasibility and superiority of this theory.are verified through calculations. Finally based on the Theory of Unstressed State Control Method and Catenary Cable Element, the problem of calculating single cable force during the erection of cables is solved.