摘要: Based on the compositive fatigue equation of load fatigue stress and temperature fatigue stress, the coverage-to-pass ratios of single-axle-single-wheel load and single-axle-double-wheel load were calculated by adopting cumulative damage factor.A direct calculating method of total cumulative fatigue damage of pavement structure produced by multi-axle load and a new design method of cement concrete pavement were put forward by replacing design axle load with cumulative damage factor.The accuracy and application feasibility of calculating fatigue damage produced by multi-axle load were done through a design example with two types of traffic volumes.Analysis result indicates that the acting times of multi-axle load at all points on the cross section of highway are different, and the peak value of cumulative damage of each axle load may be not at the same location.The thicknesses of worst pavement places under the traffic volumes calculated by the design method based on cumulative damage factor are all 22 cm, which meets the design requirement, and the thicknesses of other places can reduce according to the cumulative damage curve.Thereby, it can avoid the differences and localizations of present specification design method of concrete pavement based on standard axle load and equivalent fatigue consumption principle.更多>
摘要: The crack image segmentation of bridge substructure was studied by utilizing a modified C-V model.Crack clip, image filling and rotation transformation were applied for the precise extraction of crack width.The crack images of existing concrete bridge structure were taken in different illuminations, and test results were compared by using modified C-V model algorithm, adaptive threshold algorithm, morphology algorithm, C-V model and Canny algorithm.Analysis result indicates that the misclassification rate of modified C-V model algorithm is 3.02%, the operation time is 89 ms, and the values are minimum compared with other methods.Based on the comparative test on 1 000 crack images of bridge structure, the accuracy rate of crack detection is greater than 90.8%, and the mean error of crack width is less than 0.03 mm.So the modified algorithm can effectively improve detection accuracy rate, and reduce operation time.更多>
摘要: Vehicle system dynamics model with 56 degrees of freedom and wheel flat model were set up to compute vehicle dynamic responses.HHT(Hilbert-Huang transform) spectrum characteristics of axle box vibration caused by wheel flat impact were studied by using HHT time-frequency analysis method.HHT spectrum characteristics of axle box vertical accelerations caused by wheel flat and out-of-round were compared.The influences of vehicle running speed and track excitation on HHT spectrum characteristics of axle box vibration caused by wheel flat impact were studied.Analysis result shows that HHT spectrum distribution of axle box acceleration is uniform for healthy wheel, the stripe interval of vertical bar distribution for flat wheel is inversely proportional with the speed, and transverse bar distribution for out-of-round wheel.Therefore, wheel flat can be identified according to HHT spectrum characteristics of axle box acceleration.The lowest distinguishable frequencies are 30, 50, 80 Hz for Beijing-Tianjian Line irregularity, existing line irregularity in China and American three-grade track irregularity respectively.The identification band is 40-100 Hz when the running speed is lower than 150 km·h-1, but it should be widened to 200 Hz when the speed is over 150 km·h-1.更多>
摘要: The traditional optimization model of comprehensive passenger hub layout was analyzed, and the constraints of transportation mode and transfer capability were considered simultaneously. The improved optimization model of comprehensive passenger hub layout was proposed, and the improved genetic algorithm was introduced to solve the model. LINGO software was used to test the effectiveness, Solomon standard test data with 8 and 50 nodes were calculated respectively, and the improved model was compared with the classical algorithm. Calculation result shows that while calculating Solomon standard test data with 8 nodes, the average running time is 5 043 s and the optimal cost is 1 952 418 yuan by using LINGO software, the average running time is 62 s and the optimal cost is 1 955 900 yuan by using genetic algorithm and MATLAB software. While calculating Solomon standard test data with 50 nodes, the average running time is 574 s and the optimal cost is 8 500 600 yuan by using genetic algorithm and MATLAB software. While calculating AP data set with 25 nodes and hub node number is 3, the average running time is 612 s and the optimal cost is 155 148 yuan, the optimal cost decreases 108 yuancompared with the classical algorithm. So the improved model is effective. 6 tabs, 6 figs, 20 refs.更多>
