Research On Damage Diagnosis Methods For The Railway Bridge Based On Dynamic Analysis

The damage identification to bridge structure is an important content of the health monitoring system. The damage inspection and evaluation for the key bridge structures is very necessary work to know about their healthy situation, detect the damage location and the damage extent, which can not only help repair them timely and recover the load capacity, but also avoid the occurrence of disaster and protect the people's security. So it is very significant to perform research on bridge damage identification in theory and practice, and is also a hot subject in engineering field today. The dissertation are covered several parts as below, which is based on program of Jinan railway about inspection computation of Railway Bridge Analysis software.In the first part, the theory of dynamic damage identification is reviewed basing on the relative literatures at home and abroad, and some key problems, to which should be paid attention during its application, are brung forward.As for the second part, the dynamic analysis module of inspection computation program on Railway Bridge Analysis are programmed with language of Fortran according to requirement of railway bridge inspection. Comparing with large-scale current program, RBAP software possessed many advantages, such as clear implication, strong pertinence, easy to model for finite element method and to be operated, simple to output result and rapidly compute the location of adverse load, as well as automatically distributing examination load. The program can function as computing internal force and transmutation of structure under permanent load, living load and other load conditions, and vibrating frequency and types of bridge structure, as well as outputting modeling and transmutation profile, responding and vibrating curve, finally realizing display with different views, translation, rotation, editor of three-dimension figure and so on. The dynamic analysis module of inspection computation program are designed according to the equation of motion, formation of mass matrix and analysis of dynamic computation basing on finite element method of structure dynamic analysis, and explained main structure of analysis program with flow chart. The reliability of the computed results is testified with dynamic analysis module of inspection computation program based on continuous rigid bridge. As a result, it shows that the computed result of frequency by RBAP well meet with that computed by MIDAS software, and that the first ten modes coordinates are also in close agreement with the result computed by MIDAS software. So it can be concluded that the result computed by RBAP be correct.The third part is emphasized on the theoretical base of the curvature modal used for the damage identification of the bridge structure. The theory of the damage identification of the curvature modal is explained in detail from the relation of the curvature modal and the displacement modal to that of the curvature modal and the strain modal. The curvature is the second derivative of the displacement deduced by the straight beam bending deformation approximate equation, and there must be a set of curvature modal corresponding to a set of displacement modal. The same time the curvature is as straightforward as one-to-one mapping with strain. Because of that the strain is corresponding to the structure stiffness, the curvature of the structure can be used as a scale of the structure stiffness change. The damage of the structure is presented by the change of the stiffness, so it can be identified with the curvature modal. This part uses a simple damaged beam as an example to make a finite element model with RBAP analyzing the dynamic characteristic, further computes the curvature modal difference that is the curvature modal's approximate value and the curvature difference modal, and identifies with the simple beam among the different locations of the damage, the different modal step and the different damage extents with the two method of the curvature modal difference and the curvature difference modal, and finally draws a comparison on their capability of the damage identification and makes the conclusion that the curvature difference modal method could well do identification with the structure damage.The fourth part makes the deeper research for the method of the curvature difference modal used for identifying with the damage location of a long span continuous rigid frame bridge. Based on the long span continuous rigid frame bridges, this part makes a finite element model to analyze the main beam dynamic characteristic sensibility to the damage, and then segments the main beam in sections, and respectively computes the approximate difference curvature modal of each section before and after damage to identify with the main beam damage with the method of the curvature difference modal. The numerical simulation shows that this method can clearly make the identification with the damaged sections and accurately localize the damage combining with the quantitative index deduced by the curvature modal.