Model Updating Research Of A Test Cable-stayed Bridge

In the history of structure development, the emergence of each new hypothesis and theories are verified by test. This article presents the relevance theoretical knowledge of the model test, detailed information about the design and production process of the Hesheng model bridge, the static test system layout. Because the model bridge is mainly constructed by concrete material, the elastic modulus of the main beam and the tower concrete are tested at several periods.This article gives a detailed description about modal frequency-domain fitting method, stochastic subspace identification (SSI) and eigensystem realization algorithm (ERA). The covariance-driven SSI, not only from a comprehensive theoretical exposition, also developed a MATLAB program, through examples, verified the correctness of the procedure.Modal testing is an experimental method to obtain the modal parameters of structures. A number of modal tests on the model bridge are done by hammering test, the test results including the vertical and reverse mode of the main beam, the cross-bridge mode of the main beam, the bridge tower in-plane mode and the tower out-plane mode, due to the number of the vertical mode is large and the test results are more concerned by people, therefore, two hammering points are used, measured two sets of data, the final result is a comprehensive outcome of the two sets. Refer to the modal results of finite element model; the measured modal results are integrated, to provide a basis for model updating.Compared the differences of modal calculation between single beam model and beam plate model, two kinds of space finite element model, as a result of beam plate model has a more accurate simulation of the quality and stiffness distribution, the result is better especially for the reverse mode, thus the beam plate model is selected as the initial finite element model. Analysis of the impact of the internal force to current structure dynamic properties, due to the model components is under very low stress level, the impact can be neglected.Based on modal test results, model updating is done using optimization theory of conjugate gradient method, optimization of parameters are chosen through parameter sensitivity analysis, mode shape is classified, modal will match only in the same type of mode shape. With the assumption of foundation settlement amount and soil stiffness, the restrict stiffness to super-structure affords by foundation can be calculated, by optimizing the settlement of foundation and soil stiffness, the model updating achieved very good results. View the optimization results, those high-level frequencies which are not participate in optimization also become much closer to the measured results. Finally, a static load test is done, the updated model in the overall deformation of the structure with the real structure become closer.