Sensitivity Analysis Of Member Length Errors Of Flexible Tensile Structures

Pretension is the basic structural character of cable-strut tensile structures. As a kind of pre-stressed structures, the most important factor of the deviation of the initial shape and initial pre-tension of cable-strut tensile structures is the member length error (cable length error and strut length error, hereinafter referred to as "length error"). How to control the member length error effectively is the key issue in this kind of structural design, especially in the construction tensile design. This paper mainly focuses on the member length error effect of cable-strut tensile structures and carries out the following three aspects of researches.Firstly, the mathematical description of the length error effects (including the pre-tension deviation and the shape deviation) problems is given, using the Dynamic Relaxation Method without the establishment of the overall stiffness matrix to solve it, and using the catenary cable element model and its precise co-ordination equation to ensure the calculation accuracy. The sensitivity matrix to reflect the relationship between the pre-tension deviation and the length error is established. One method of how to select the initiative cables to pull in project is proposed. Taking into account that the actual construction shaping of the structures is based on controlling the cable tension, the solving strategy of the length error effects which is based on Newton Method with the existence of cable force constraints is further proposed, pointing out that the ability to control the length error effect effectively is an important basis of the evaluation of the reasonableness of cable-tensile program.Secondly, to solve the sensitivity issue of length error in the pre-tension process of flexible cable-strut tensile system, Sobol's sensitivity analysis method based on variance is used. Using the derived analytical expression of the length error sensitivity matrix to compute and analyse the sensitivity indicators of each order of two different pre-tension cable-strut tensile structures, and comparing the effect of the different programs on initial pre-tension of the structures. The advantages, disadvantages and effectiveness of Sobol's method in length error sensitivity analysis are discussed.Thirdly, facing the problems of evaluating the actual pre-tension state of cable-strut tensile structures and adjusting the deviationg of the pretension, a strategy based on Genetic Algorithm of solving the worst combination of cable length error of cable-strut tensile structures and a method of analysing how to derive the corresponding combination of cable length error when knowing the measured initial pre-tension is proposed. With a mast cable-stayed suspension system in the actual project, using the method above to solve the worst combination of cable length error and analyse the deviation of the measured pretension, and discussing the advantages, disadvantages and effectiveness of Genetic Algorithm when analyzing the above issues.