Bridge Structural Damage Identification Of Strain Mode

Traffic is a social economic blood, and a bridge is a traffic throal. The development of social economy will be limited if the traffic docsn't move to and from, So it is very important to make sure every bridge' s function and safety. To use every bridge normally as demands to test or moni tor to bridges' safety from now and then. At, present there are a large quantity of bridges in our country, one hand, many old bridges have approached their design lifetime, their components have aged and be damaged, on the other hand, a number of new and large-scale bridges will be built. To assure these bridges' safety and to avoid accidents, we should get on monitor on-line to new bridges, and detect damage and identify reliability to old bridges. The traditional testing approaches can' t make sure a bridge' s damage positions and rest lifetime, and it will take plenty of time and interrupt traffic. So it has an important realistic significance to explore a simple rapid approach to detect bridges damage . the paper' s objectives is to quest a proper approach to detect bridges damage.The research of approach to monitor bridge health state has become a hot spot which social and technologic people have explored through the theory of, dynamics of structures and the lest technology. Structure mode parameters(vibration frequency, mode of vibration and damping)are the functions of physical property parameters(mass, rigidity, damping). The damage of structures certainly leads to the transformation of physical property parameters. The damage state of a bridge can be identified through the transformation. The parameters of strain mode do so. The paper' s main contribution is followed beiow.l.The paper studies the theory to detect damage of bridges, and compares many sensitive parameters to detect bridge damage through correlative literature all over the world, finally concludes it suitable that bridge damage is detected by strain mode parameters. The strain mode parameters satisfy four foundstiona.l conditions as follows: ㏕hey are sensitive to sectional damage and they are monotone function of structure damage. @They have determinate location coordinate. (3)0n the damage location, the curves of difference of strain mode have evident peaks. @0n no damage location, the variety amplitudes of the peaks of difference of strain mode are less than posited threshold value in advance. The strain type parameters compare favorably with the nature frequency and thedisplacement parameters on detecting structure damage.2. The paper derived the formulae for the strain response mode with the knowledge of dynamics of structures, of materiaJ mechanics, of elastic mechanics, and pointed out their use range. A computer program is worked out with FORTRAN POWER STATIONS 4.0, It can compute the characteristic value, the characteristic vector and the strain mode for a bridge structure, and it is verified correct. The program used near elements' vibration displacement to predicate a bridge' s strain when it computed the strain mode of a bridge. To some extent, as solved measuring means to detect structure damage with strain mode approach.. The program' s computing result certified that bridge damage' s location and degree could be delected not by the approach of strain mode, but by the curve difference ol' strain mode.3.In the paper, some of numerical simulation were respectively done on damage detection of bridges of simply supported beam, continuous beam, and rigid-jointed frame. Bridges' damage degree was simulated with the percentage of reduction of bending r igidi ty . Every bridge' s damage modes were divided by following types:( I ) A unit was damaged in different degree. (II)Al the same time ,several units were damaged in the same degree. (III) Several units were damaged in different degree. (FV) A bridge was divided by different finite elements. Through some of numerical simulation, some conclusions were drawn out as following:The damage positions of bridges can be accurately identified by the approach of strain mode.The dam...