Finite Element Model Updating And Safety Assessment Of Bridge Structures Based On Improved Response Surface Method

The design life of bridge structures is decades or even hundreds of years.During its service life,due to the external and environmental loads,the bridge structures will inevitably suffer from different degrees of damage,resulting in a decrease in the load carrying capacity and durability of the structure,and even catastrophic collapse accidents in severe cases.With the rapid development of computer technology and finite element method,the static dynamic properties of the structure under various loads can be calculated and analyzed faster by using finite element simulation method,so as to realize the safety assessment of the structure.However,since the finite element model is usually established based on the design information,the initial finite element model cannot accurately reflect the force characteristics of the real structure because the structural stiffness of the bridge structure will be reduced after service due to the accumulation of damage and there are errors with the design information.Therefore,the initial finite element model needs to be updated by structural health monitoring data,so that the structural static dynamic response obtained by the updated finite element model is close to the actual measured value.At present,the finite element model updating method based on response surface method is widely used in civil engineering,which is characterized by high computational efficiency and clear physical meaning of the updated parameters,but there are also problems such as limited fitting accuracy and non-unique solutions,which need to be further studied.To this end,this paper systematically investigates the finite element model updating method for bridge structures based on the improved response surface method using theoretical analysis,numerical simulation and health monitoring.The specific research work is as follows:(1)By introducing the radial basis function as the augmentation term of the polynomial function,the response surface model based on the augmentation polynomial is established,and the fitting accuracy of the global response surface model is improved.By improving the regression step and annealing strategy in the simulated annealing algorithm,the convergence speed and accuracy of the optimal solution of the response surface model are improved.The numerical model of the simply supported beam was established by using ABAQUS finite element analysis software,and the relative errors of the updated results before and after the improvement were analyzed,and the noise robustness of the method was verified.It is shown that the maximum relative error of the updated parameters of the simply supported beam is reduced from 13.011% before the improvement to 0.719% after the improvement,and the maximum relative error of the self-oscillation frequency is reduced from 0.728% before the improvement to 0.225% after the improvement,and the number of convergence steps is reduced from 1000 to 100;at 5% and 10% noise levels,the maximum relative errors of the updated parameters of the simply supported beam are 2.651% and 6.368%,the maximum relative error of the natural frequency of the structure is 1.276% and 5.697% at 5% and 10%noise levels,respectively.It can be seen that the finite element model updating method based on the improved response surface method has high updating accuracy and updating efficiency,and has good noise robustness.(2)The finite element model of the main bridge was updated based on the improved response surface method,and the relative errors of the updated results before and after the improvement were analyzed.The study showed that the maximum relative error of the selfoscillation frequency of the finite element model of the main bridge was 21.68% before the update;the maximum relative error of the self-oscillation frequency of the structure was reduced to 8.44% after the modification of the model based on the traditional response surface method;the maximum relative error of the self-oscillation frequency of the structure was reduced to 4.23% after the modification of the parameters based on the improved response surface method,which was 4.21% lower than the maximum relative error of the traditional response surface model update method.4.21% lower than the maximum relative error of the traditional response surface model updating method,and the updating effect is good.(3)A bridge structural safety assessment calculation process was established to evaluate the safety of the main bridge of the Tonghe Songhua River Bridge using the updated finite element model of the main bridge of the Tonghe Songhua River.The design loads were applied to the finite element model to calculate the safety threshold of the structure in the limit state,and the evaluation values of the bridge strain and deflection indexes were calculated by combining the monitoring data during April,May and June 2021,respectively,to comprehensively calculate the evaluation value of the main bridge of the Tonghe Songhua River Bridge and assess the safety status of the bridge.The study showed that the overall rating of the main bridge of Tonghe Songhua River Bridge was 82.781,and the rating belonged to good(category 2)safety state;the bridge had slight defects,but there was no impact on the bridge function,and it was suggested that the bridge should be continuously monitored subsequently to collect a large amount of stable and reliable long-term monitoring data to adjust the evaluation value of the safety assessment and keep an eye on the bridge safety state.