| As an innovative achievement of modern bridge design and construction,orthotropic structure is widely used in various steel structure bridges.However,due to the complexity of this structural form,Severe fatigue cracking of bridges during service.In addition,it makes this problem more prominent that the increase of traffic volume and the large number of overloaded trucks.In this paper,aiming at the problem of frequent cracking of roof-longitudinal rib connection details of orthotropic steel bridge deck in service,the efficient detection,identification and fatigue life evaluation of orthotropic steel bridge deck are carried out.The main research contents are as follows:(1)Based on the structural characteristics and fatigue crack types of the roof-longitudinal rib connection details of orthotropic steel bridge deck,an intelligent detection robot is designed in this paper.The robot was designed as a lower-walking system and an upper-detection system according to its functions.After the lower-walking system receives the acquisition command,it controls the electromagnets to adsorb alternately to move the robot to the detection area.Then,the ultrasonic phased array probe is arranged in the roof position to complete the local detection by using the upper-detection system.(2)Based on the measured data of the roof-longitudinal rib connection details of orthotropic steel bridge deck of the Yichang Yangtze River Highway Bridge,the corresponding ultrasonic phased array image data set is established.Based on the characteristics of image data,the denoising method of adaptive median filter and the image enhancement method of restricted contrast histogram equalization(CLAHE)are used to preprocess the phased array image.Combined with subjective evaluation and objective evaluation indexes,it shows that the preprocessing effect can effectively protect the local information of ultrasonic phased array.The yolov5 s network model is improved based on data enhancement and attention mechanism.The results show that the model with coordinated attention mechanism has the best effect on the basis of data enhancement.And the three indexes of Precision,Recall and m AP are 93.31%,89.22% and 95.11% respectively,which are improved by 3.69%,0.54% and 0.59% respectively.(3)Based on the multi-scale finite element analysis model of orthotropic steel bridge deck roof-longitudinal rib connection details,the residual life of cracks with different depths is evaluated combined with the measured crack data.The research results show that: the detail weld of roof longitudinal rib connection is an I-II-III mixed crack dominated by mode I crack,and the crack surface will deflect at a certain angle due to the influence of mode II-III crack in the process of crack propagation.As the crack front gradually moves away from the stress concentration area,the internal force of the section is redistributed,so that the stress intensity factor at the crack front increases first,then gradually flattens or even decreases with the increase of crack depth.The welding residual stress has little effect on the amplitude of the stress intensity factor,but the stress mode of the roof-longitudinal rib connection details is changed from the tension-compression mode dominated by compression to the tension-tension mode,which promotes the development of cracks.Considering the influence of residual stress,the evaluation results of structural fatigue life are partial to safety,which can also provide a certain reference for later determination of bridge inspection interval.The residual fatigue life of 4mm crack at the weld toe of L/8 section and L/2 section is 4.08 years and 5.1 years respectively. |
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