Research On Method Of Detection And Bearing Capacity Assessment To Saide Bridge

Bridges are the throat of traffic,and traffic capacity of bridges determines directly the transport capacity.As is known,bridges are complex structure systems consisted of steel and concrete.On the one hand,variation caused of design,construction and materials may lead to the uncertainty of bridge structural bearing capacity.On the other hand,with the extension of bridge service period,any bridge may appear damage of different degrees,resulting in the degradation of bridge using functions.Because of the universality of bridge function injury,any country has no ability to replace or newly build a large number of bridges of this kind.Foreign data shows that,the capital required for maintenance and reinforcement of existing bridges is general about 20%t of newly built bridges.Statistical data of highway department in our country also shows that,the cost of bridge maintenance is about 10%-20% of newly built bridges.As for the bridges of function injury,firstly,practical bearing capacity and live load grade of these bridges should be determined,in order to dig out potential traffic capacity of bridge structures.Secondly,methods of reinforcement and maintenance for some unqualified bridges are used to meet the requirement.While the two disposal methods are required to detect the bridges,and make accurate evaluation of bridge bearing capacity,basis on detection results.Main existing detection methods of concrete bridges consist of three major types:nondestructive detection,static detection and dynamic detection.Nondestructive detection is a method which can determine physical properties and geometric changes of bridge structures by using detecting instruments.For example, concrete strength and carbonation depth can be determined by nondestructive detection.Geometric parameters such as fracture distribution and foundation displacement of bridge structures can be determined by geometric measurement.Based on the tested physical properties and geometric changes,evaluation of the bridge usage stage is carried out by certain methods.But the results from the method is greatly influenced by human factors.Static detection is a method which can judge the bridge usage stage,by measuring static parameters(strain,displacement) of specific section under specific loads.Dynamic detection is a method that dynamic parameters(vibration mode,frenquency and damping ratio)of bridge structures is defined by modal analysis of measuring some bridge dynamic response,and bridge usage stage is judged based on dynamic parameters.Static and dynamic methods of bridges are the methods that usage stage is evaluated based on the tested mechanical properties.The two methods are little influenced by human factors,and the precision is hige.Beacuse of complexity of static and dynamic detectioin methods,there is no unified and effective standard of static and dynamic detection methods.Based on the situation above,starting from basic theory,relying on the project of Chang Chun Saide bridge,research on bridge static and dynamic detection technology is carried out.And bearting capacity of Chang Chun Saidu bridge is evaluated based on tested static and dynamic parameters.Main research work carried out in this paper is as follows:1.Starting from the basic principle of finite element,basic principle and course of static and dynamic analysis are discussed by using finite element method.Based on finite element theory of static and dynamic analysis,the course and method of solution and calculation model building of bridge theory are definited by using MIDAS/Civil.The theoretical calculation model of Chang Chun Saide bridge is established,by using the theory above as guidance.And basis on the calculation model,static and dynamic parameters of the bridge are calculated2.Starting from the objective and basic principle of bridge static detection,measurement items and selection methods of sensors in bridge static detection are degineted.Combined with theoretical analysis,basic principle and methods of test load determination are discussed,and basic course of static detection is summarized.In the same way,starting from the objective and basic principle of bridge dynamic detection,measurement items and selection methods of sensors and exciting methods in bridge dynamic detection are degineted.Based on basic principle of structural vibration,dynamical measuring points are optimized by using effective independence.Combined with random decrement technique and eigen-system realization algorithm,modal analysis technology of bridge structure vibration mode,frequency and damping ratio from random response are formed.Basis on theory and methods above,static and dynamic detection are carried out to Chang Chun Saide bridge.The required test data is obtained. 3.Evaluation index of bridge stage corresponding to each static parameter is defined.Evaluation methods of bridge stiffness,strength and transverse connection basis on static parameters are discussed.Methods of bridge damage identification basis on mode orthogonality are proposed.It draws a coincident conclusion,when each evaluation method is used in the stage evaluation of Chang Chun Saide bridge.Consistency of the evaluation result proves the correctness and effectiveness of the method proposed in this paper.