Study On Dynamical Detect Technique And Damage Evaluation Of The Overcrossing Bridge ChangChun

Currently,there are large quantities old bridges in the our country. And many of them have different degree defect and damage in function. According to the research result, the load capacity of bridges among the permanent big and medium-sized bridges in country roads, the province roads and county roads in the whole country up to the standard only take 6.53% of the whole quantities bridges. The bridges which meet the load standard take 9.17%.And others take 84.3%, which mostly meet. Although most highway bridges were built after foundation of our nation, the bridge ages generally in 30 years.Therefore, the disease have not exposed in quantities. However, the phenomena of aging, damage, danger bridges increase year by year. And the load capacity decrease distinctly.Because of the imperfect function and damages, large quantities replace and newly built methods are not adopted in any country. The foreign data show that the funds needed to build new bridges take 20% of the funds needed to repair or strengthen old bridges. The experience of the highway department in our country also indicates that the funds needed to build new bridges take 20% of the funds needed to repair or strengthen old bridges. So the measures should make correct estimation on operation status, damage degree and surplus life and etc as the base. Firstly, the capacity of the bridges in existence should consider fully. Secondly, the methods strengthening bridges are adopted to meet the requirements.The load test is the method used commonly to detect the current bridges, which contain static load test and dynamic load test.â‘ The static load test is to carry the equivalent load to the design load. And the strain, deflection, cracking, developing trend and transverse distribution coefficient in control part and section are tested using apparatus.â‘¡The dynamic load test is to carry the action of car, skipping, braking dynamicor stabilization, instantaneous and other manners. The dynamic response in control section is tested by apparatus. And from the result the dynamic parameter such as frequency, vibration shape, damping and impact coefficient and so on can be obtained.The damage evaluation based on the static test is to arrange static load in the most disadvantageous position according to the design load grade or to determine the position according to the control force. The static displacement, strain in concern section is to be measured. From the result we can know the bridge capacity and validate design theory and calculation method. So the ultimate capacity is determined.The dynamic test technique has already been applied in the fault diagnose, identification and dynamic modification in aerospace and precise machine etc. aspects. The damage evaluation based on the dynamic test belongs to the overall detect technique. It can acquire full information, especially in the indistinct position. Also, the detect precision less rely on the engineer experience and subjective judgment. In addition, it can evaluate safety store and the degenerative path systemically.The paper carries vibration test on a factual prestressed reinforced concrete continuous box beam with three-spans under the condition of environment encourage. And do static load test on this bridge. Based on the dynamic test data, the damage position is determined with changing flexibility method. After the damage position determined, finite element model modified technique is used to determine the damage degree of the box-beam bridge based on the static test data. The paper contains the following contents:(1) Firstly, the paper studies the dynamic load test technique under the condition of environment random encourage.(2) Secondly, the paper studies the static load test technique on prestressed reinforced concrete continuous box beam with three-spans.(3) Thirdly, the paper studies the method that how to change the flexibility todeterminer the damage position on prestressed reinforced concrete continuous box beam with three-spans.(4)Fourthly, the paper studies the method using finite element model modified technique to determine damage degree on prestressed reinforced concrete continuous box beam with three-spans based on the static test data.