Application Of Digital Image Detection In Reinforcement Steel Truss Bridge

With the increasing improvement of social transportation in recent years,bridge construction is also developing in the direction of larger spans,lighter weight and higher strength.Steel truss bridges undoubtedly conform to this development trend.In the past,due to imperfect design concepts and non-standard construction and other reasons,the bearing capacity of some steel truss bridges has declined,and the lateral amplitude has exceeded the limit during operation.This paper uses steel strands to simulate external prestress to reinforce the steel truss.The accuracy and feasibility of the image detection technology in detecting the static load test and modal test of the truss and the accuracy of the image detection technology in measuring the equivalent stiffness of the cable are determined..The main work and achievements are as follows:(1)Place the traditional acceleration sensor on the top surface of the test steel truss,and then import the acceleration history into the DASP system for analysis,and obtain the first two modes and frequencies of the truss in the vertical direction.Place the sensor on the side of the test steel truss to obtain the first two modes and frequencies of the truss in the lateral direction.Finally,the sensors are arranged on the top and side at the same time,and the frequency of the truss under torsional vibration mode is obtained.At the same time,place a dial indicator in the truss span to measure the deflection of the truss span after loading.(2)Establish the finite element model of the steel truss bridge in Midas civil.It isbased on the static load test and modal test results measured by traditional test results.The analytical method and the dichotomy method were used to modify the finite element model respectively,and the natural frequency and deflection of the modified finite element model were compared with the modal test results in the traditional detection method.The model modified by the dichotomy is used for subsequent research.This work can be concluded that both the dichotomy and the analytical method have the ability to accurately identify the stiffness of the bolt,but the dichotomy does not need to understand the relevant parameters of the bolt and the identification efficiency is higher.(3)At the same time,the equipment was used to record the vibration process of the steel truss bridge at the same time.The video was decomposed to convert each frame of the video into an image.After a series of processing such as cropping and graying of these images through MATLAB,the canny operator was used.The edge of the image is detected,and the time history data is imported into the DASP system to obtain the corresponding vibration mode and natural frequency.Comparing the modal test and static load test results measured by the image method with the traditional method,it can be found that the image method can accurately measure the natural frequency of the truss and the mid-span deflection under load.At the same time,the image method has the advantages of no contact,many measuring points and high efficiency.It is worth promoting in actual projects.(4)Consult the relevant data to obtain the relationship between the elastic modulus of the cable material and the frequency,use the image method to measure the frequency of the cable in the simply supported state,and then use the frequency to calculate the elastic modulus of the cable material.The calculated elastic modulus agrees with the actual.This work proves that the image method can accurately obtain the elastic modulus of the cable material itself by measuring the cable frequency.After considering the lateral displacement stiffness of the truss,the displacement of the cable is measured by the image method,and the equivalent stiffness of the cable is calculated from the displacement.Then the simulation and verification are carried out in the finite element.It is proved that the image method can accurately measure the equivalent stiffness of the cable.(5)Study the influence of external cables on the truss reinforcement effect.In turn increase the elongation of the cable to increase the tension of the cable.Then perform the static load test and modal test of the truss,and observe the results of the static load test and modal test of the truss.Keep the parameters of the cable unchanged in the finite element,modify the cable layout,perform the finite element static load test and modal test after reinforcement,and compare the static load test and modal test results before and after reinforcement.It is found that the higher the degree of tension in this experiment,the better the reinforcement effect.In this test,the greater the distance of the trapezoidal cable from the truss edge,the better the reinforcement effect.The reinforcement effect of the trapezoidal arrangement is better than that of the V-shaped arrangement.