Analysis And Control Of The Geometrical Error Effect Of Cable-bar Tensile Structures

Pretension deviation and shape deviation caused by the structural geometrical errors is called geometrical error effect(GEE). How to control GEE effectively is a key technical issue in construction of cable-bar tensile structures. Based on the cable-length deviation and the objective of GEE controlling, specified to cable-bar tensile structures three parts of work were done as follow:(1) Stochastic model of cable-length deviation was set up. For linear cable-bar structures and nonlinear cable-bar structures, the fundmental equations of pretention deviation, shape deviation and cable-length deviation was deduced respectively. Further, on the condition that the pretension deviation of active cables was zero, the formula which reflects the equation between pretension deviation of inactive cables and cable-length deviation was obtained. According to the stochastic model of cable-length deviation and the formula, the statistical characteristics of pretension deviation could be obtained. In the two examples of cable-bar structures, the distribution and size of pretension deviation under different pretensioning schemes were compared. The effect of GEE controlling changes in pace with the variety of active cables, and that could be used to assess the pretensioning schemes.(2) The issues of monitoring and compensation of the tension deviation for cable-bar tensile structures were researched. Based on the basic formula which reflects the relationship of cable-length variation of active cables and the variation of internal force, the principle of determining the minimal number of inspected members was discussed by analyzing the properties of that formula's roots. A method for locating the effective inspected members was also suggested by means of the variance sensitivity analysis of axial force increments of members to length increments of active cables. Equations were further deduced to calculate the tension deviation of active cables or their approximate least square solution according to the axial force deviation of inspected bars, and a parameter was defined to reflect the influence of relaxation of passive bars. The method for calculating the compensatory tension forces was set up.(3) The sensitivity of cable-length deviation can be used to decide that which pretensioning scheme should be used in construction. The method of sensitivity analysis based on variance was introduced. Sensitivity factor was used to rank cable-length deviations in terms to their contribution to the variability of the object, and based on that, the active cables could be selected. In the end, using genetic algorithm, strategy which could search for the best active cables automatically was put forward. Computation program was written and the validity was tested by examples.