Nonlinear Damage Identification Method Of Breathing Crack In Vehicle-Bridge System

Concrete crack is one of the common damages of concrete simply-supported bridges, which are mostly extensively used in medium-small sized bridges in China. Characterized by enormous quantity, versatility and simple structural form, for this type of bridges, health monitoring system with multiparameter and multipoint cannot be built like complicated bridges. Consequently, it is of significant practical value in engineering for simple and effective structural damage detection based on dynamic behavior of these bridges under running condition. From test observation, a crack can be open and closed regularly during the vibration, like breathing effect. A curvilinear model based on curvature control for breathing crack is established and blended into vehicle-bridge coupling vibration system. By theoretical derivation and analysis on acceleration response signal of vehicle-bridge system with breathing cracks, nonlinear damage identification method of simple beam based on energy indexes is proposed, making it possible that crack damage detection of simply-supported beam in operation status through several sensors.The main research contents and results of this paper are as follows:(1) The calculation program of vehicle-bridge system with breathing cracks is compiled. The program is based on principle of interactive force by using half-vehicle model and Euler beam. The curvilinear breathing crack model controlled by curvature is added to the program by the way of stiffness reduction. By comparing with the existing calculation results, the program is proved to be correct.(2) The Hilbert-Huang Transform is improved. Aiming at the end effect and mode mixing problems, the image continuation method and EEMD are used to eliminate this two defects. Through the example analysis, it is shown that the improved Hilbert-Huang Transform can be correctly used in signal processing in vehicle-bridge system.(3) A nonlinear damage identification method of simple beam bridge in operation status is proposed. The method based on energy indexes is established by analyzing the distribution law of the vibration signal energy of the concrete simply-supported beam with cracks and considering the theoretical derivation. Through numerical examples, it is proved that the method can determine the existence, location and extent of the crack through one sensor.(4) The applicability of the damage identification method is discussed. Many different factors are into consideration in numerical examples, which contain noise, vehicle condition, environmental temperature and the condition with multiple cracks. The results show that the factors, including noise, vehicle weight, vehicle type and environmental temperature, have no effect on the results of the damage identification method. The speed of vehicle have a great impact on the results of the extent of damage. Too large speed can also effect the damage identification results when the beam has multiple cracks.(5) The arrangement of sensors has been optimized based on the principle of global optimization. In all damage conditions with different positions, it is the best selection of the arrangement of sensors when the mean of amplitude ratio is greater, the variance is smaller and the number of effective monitoring points is larger. Considering this three aspects and calculating the optimal coefficient, it is shown that the mid-span of the beam is the best position to arrange the sensor.