Nonlinear Damage Identification Method Of Concrete Simply Support Beam Based On Improved HHT

The medium and small span simple supported beam bridges are one of the main bridge types in China's road transport.However,under the combined effects of initial defects,long-term changes in vehicle loads,and the overload of emergency,the simple supported beam bridges are prone to cracking,which affect the durability of the structure and reduce its carrying capacity.Due to the simple structure and large number of this type of bridges,the feasibility and the economical efficiency of building a fully functional bridge health monitoring system for this type of bridges are low.Therefore,under the action of operational loads,how to realize the damage identification of cracks simply and efficiently is the core issue to solve the safety service of such bridges.Based on the vibration principle of vehicle-bridge coupled vibration system and the characteristics of time-varying model of breathing crack stiffness,this paper uses MATLAB as the platform to compile the finite element program,adopts the improved HHT transform to analyze the dynamic response signal by time-frequency analysis,a crack damage identification method based on energy is proposed,and a sensor can be used to identify the damage status,crack location and degree,and provide method support for crack identification of concrete simply supported beam bridges.The main research content and conclusions of this article:(1)The finite element program for vehicle-bridge coupled vibration with nonlinear damage is programmed.A four-degree-of-freedom semi-vehicle model and a Euler beam model were used to couple the vehicle and the bridge through the vibration principle of the vehicle-bridge coupling system,and a model of the breathing crack was incorporated into the bridge unit.In this paper,the general expressions of the nonlinear stiffness of breathing cracks are deduced from the principle of curvature ratios and sinusoidal breathing crack models.The simulation results and the calculation process of two models for breathing cracks are compared.Finally,the sine function breathing crack model with good precision was used to simulate the cracks in the process of vehicle crossing.(2)Improved modal aliasing and noise residuals in HHT transformation.The complementary ensemble empirical mode decomposition(CEEMD)is used to improve the modal aliasing problem of Empirical Mode Decomposition(EMD)and analyze the effect of the added white noise signal amplitude,modal aliasing by times and noise residue.The analysis results show that adding 0.1 times white noise and integrating an average of 100 times can solve the problem of modal aliasing and noise residue at the same time.(3)A nonlinear damage identification method for concrete simply-supported beam bridges under operating conditions is established.Using CEEMD analysis method,combined with the correlation calculation to select the more sensitive to the damage of the intrinsic mode component,using HT to calculate the vehicle's energy history of the bridge,and then through the time and amplitude of the damage peak to identify the location and degree of cracks,a nonlinear damage identification method for cracks was constructed.Numerical examples verify the accuracy of the proposed method for the damage state,damage location and damage degree.(4)The applicability of nonlinear damage identification method for cracks of simply supported beams under different parameters is analyzed.The white noise is added to the analog signal to simulate the test noise.The results show that with the noise of 5%,the wavelet threshold de-noising method can be used to achieve the fine location of cracks.The results show that the vehicle weight and vehicle type have no influence on the proposed method.The vehicle speed has less influence on the damage location and has a greater impact on the damage degree identification and the proposed method is suitable for low-speed operating conditions.By setting up different multi-crack conditions,the location identification effect of the proposed damage identification method on multiple crack positions is verified.By varying the elastic modulus of the concrete to simulate the temperature change,it is shown that the temperature has no effect on the recognition effect of the proposed method.