Adaptive Cable-Strut Tensile Structures Theory And Experiment

An adaptive cable-strut tensile structure with length-adjustable members is defined as a smart structure which can actively adjust its configuration to improve its adaptability to the variation of operational environments by changing the length of members. Aiming at the shape control of adaptive cable-strut tensile structure and based on its mechanical characteristics, this thesis has conducted intensive research on the key technologies, including the calculation of length changes, minimum quantity and optimal placement of adjustable members.By synthetically utilizing the decomposition theory of equilibrium matrix, nonlinear programming theory and nonlinear finite element theory, the mechanism of adaptive cable-strut structures has been analyzed systematically. The formulae on structural nonlinear responses to the length changes of members are derived and the solving strategy is provided. The proposed methods and strategies are appropriate for any type of cable-strut tensile structures under any load cases, providing the theoretical basis for the analysis on adaptive cable-strut tensile structures.With the shape and internal forces control as the objectives, and taking the length changes of active members as the unknowns, the incremental relation between the target responses and length changes has been derived based on NFEM. Both the incremental iterative strategy and the error feedback iterative strategy are proposed for solutions of this problem. Further, taking the constraints on internal forces and limited length changes of active members into account, a nonlinear shape control optimization model has been established. Based on the relation between target response and length changes, an sequential quadratic programming algorithm(SQP) has been proposed.Based on the finite element equilibrium equation, the sensitivity of structure responses to length changes has been derived. Furthermore, the first and second order sensitivities of objective functions on shape control, internal forces control and stiffness control are derived, providing the gradient information for the SQP algorithm. The sensitivity analyses proposed are applied to a Geiger cable dome and a tensegrity structure respectively, the control efficiency of active cables and active bars is discussed, and a criteria for the selection of active members is proposed.Moreover, based on precisely controllable conditions and the property of linear equations, the coefficient matrix for calculation of incremental length changes has been studied, and the mathematic relationship between the solutions of equations and active members’number and placement is revealed. The criteria for the layout of active members are proposed. An optimization model for the placement of active members with the minimum length changes as the objective has been established. A genetic algorithm(GA) is proposed to solve the problem. Further, a multi-objective control model with the minimum shape errors, minimum length changes and minimum number of active members as objectives has been established. A hybrid algorithm is proposed to solve the problem, which is composed by non dominant sorting genetic algorithm(NSGA-Ⅱ) and SQP. Results from the proposed algorithm show the restriction between different optimal solutions, providing reference for deciders to make an optimal plan.Based on the proposed theory, a small model of a Geiger cable dome with adjustable members was designed to carry on the experiment investigation. The pre-stressing progress, length adjusting and structure responding progress, and shape control progress were all investigated. Results show that, the experimental pre-stress was consistent with the theoretical model; the experimental trend of sensitivity analysis was consistent with theoretical analysis; the favorable control effect on the model guided by analytical scheme verified the validity of theoretical algorithms.According to the strategies and algorithms proposed in thesis, computer programs for the analysis and control of adaptive cable-strut structures are developed based on MATLAB. It’s capable to apply systematic analysis and control on any cable-strut structure with given topology by such programs.