Research On Identification Of Breathing Crack Damage In Bridge Under Vehicle Load

Concrete bridges with small and medium-sized spans are widely used in elevated transportation lines in China.With the extension of service period,damage will inevitably occur,and cracks are one of the main forms of damage for such structures.Compared with the traditional open crack model,the breathing crack model takes into account the time-varying nonlinear characteristics of bridge cracks,and can better describe the opening and closing effect of bridge cracks under vehicle load.It is of great significance for damage identification and safety assessment of bridge structures.The method based on signal processing has a unique advantage in the signal singularity detection of nonlinear systems,and the modelless damage identification method based on it is expected to solve the problem of damage identification of bridge breathing cracks under vehicle load.Based on this,this paper aims to investigate the nonlinear damage of breathing cracks in small and medium-sized span bridges under vehicle beam loads,and to study a signal processing based damage identification method for bridge crack states.The main research contents and conclusions are as follows:(1)According to the principle of vehicle-bridge interaction,the vehicle and bridge were coupled,and the numerical modeling and dynamic response calculation were realized by developing the finite element program.The rationality and dynamic characteristics of the model were analyzed based on the engineering background of the simply-supported beam bridge of the elevated line.The results indicate that the model can reasonably simulate the stress and deformation of this type of bridges under operating conditions,and can serve as a benchmark model for subsequent research.(2)The breathing crack model was embedded into the bridge model,and the finite element program of the vehicle-bridge coupling system including the breathing crack model was developed,and the influence of the breathing crack damage degree and vehicle speed on the dynamic response of the bridge was investigated.The results indicate that the nonlinear effects of breathing cracks on the dynamic response of bridges are amplified with the increase of damage degree and vehicle speed.The acceleration difference at different measuring points of the bridge can reflect the single damage location of the breathing crack,and the closer the measuring point is to the damage location,the more obvious the effect is.For multiple damage with large spacing,the difference of acceleration response of measuring points can determine the approximate location of damage.(3)The acceleration difference of the bridge before and after damage was decomposed and reconstructed by wavelet analysis,and the damage location,range and degree of the bridge breathing crack are identified by high-frequency wavelet coefficients,and the impact of uncertain factors such as speed and noise on the damage identification was considered.The results show that the time when the train passes through the damaged area can be determined by the maximum value of the wavelet reconstructed signal amplitude of the bridge acceleration difference,and the damage location and damage range can be calculated.The relative damage degree can be recognized by using the reconstructed signal energy,and the speed and test noise have little influence on the recognition effect of the proposed method.The method proposed in this paper can be used to identify the location,range and degree of breathing crack damage from vibration response of a few measured points of bridges and its derivative indexes under vehicle load,which can provide a new way for the disease detection of bridge breathing cracks in engineering practice.