Inverse Analysis for Geometric Configuration Adjustment and Closing Analysis of Cable-stayed Bridges Min Kwon Lee
ABSTRACT The undeformed geometric configuration of cable-stayed structures cannot be defined because the lateral stiffness of a cable is developed from applied tensions. Therefore, either the unstrained length or the tension of cable must be calculated from the given design deformed geometry. Determining either unstrained length or tension that satisfies the given geometry in equilibrium is defined as an initial equilibrium state analysis. Initial equilibrium state that determines standard geometry for the other live loads and dynamic analysis is very important. Initial equilibrium state analyses by geometric constraints and by minimizing moments guarantee uniqueness of solution and draw the exact solution. But a method by geometric constraints has a problem of developing excessive cable tensions and by minimizing moments can be got configuration out of target profile. So this paper presents a new analysis, hybrid TCUD analysis which is based on both the method by geometric constraints and by minimizing moments for overcoming these demerits. Correction of target configuration is very important in construction for cable-stayed bridges. However slender structures like cable-stayed bridges are difficult to construct with accurate design values because of construction conditions, uncertainty of loads, and manufacturing errors of each members. Therefore, correction procedure should be performed estimating the current state of structures. This study presents inverse analysis for cable-stayed bridges by determination of a design value and the regularization method for removing instability. Geometric configuration adjustment is presented by adjusting cable lengths based on estimated actual variables using Monte Carlo simulation. Cable-stayed bridges that constructed by free cantilever method do not satisfy compatibility condition because two independent structure systems are made up and no forces are on the closing section before closing the girders. Thus, pull-up force of derrick crane and cable tensions are added to satisfy compatibility of displacements. This study presents the method of calculating displacement sensitivity and solving nonlinear compatibility equation including sensitivities by Newton-Raphson method. Monte Carlo simulation is employed to estimate errors during construction stages. The example of second Jido Bridge is performed to demonstrate the validity and the effectiveness of the proposed methods for geometric configuration adjustment.
Key Word Hybrid TCUD analysis, Inverse analysis, Closing analysis, Regularization, Sensitivity
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