Research On Damage Identification Method Of Typical Engineering Structures

Engineer structures are inevitably damaged for various environment, such as external loads, material aging, corrosion and fatigue damage. Some of the damage which is in the internal structure with the naked eye. When the damage accumulation goes to a certain degree over time, it will affect the normal use of the structure and even lead to destroy. Which is a serious threat to the security of structure. The more early discover and repair the damage, not only can greatly reduce the cost, but also can prevent the accident. Therefore, researching on the method of structural damage identification has important engineering significance.Damage generally produce changes in the structural properties?stiffness, mass and damping. etc?, and these changes are accompanied by changes in the modal characteristics of the structure?natural frequencies, mode shapes, and modal damping?. Some literatures pointed out that the modal flexibility is more sensitive to local damage than the natural frequency or mode shape, and thought that it can be well used to identify structural damage and the degree of damage. This phenomenon has been widely used by structural engineers for detecting damage. Therefore, the study of modal parameters for structural damage identification has received much attention by many researchers. In a word, the key task in various identification methods as follows:1)Whether the damage is existence in the structure; 2) To determine the damage location of the structure;3)To quantitative analysis the damage degree of the structure;4)To evaluate the residual service life of the structure.This article uses flexibility matrix difference of before and after damage.Proposed a new damage identification method based on relative flexibility curvature matrix, and building two indicators to identify damage. The main contents as follows:1) Introducing the background and meanings of selected topic, and discussing the historical process with the trend of damage identification;2)Introducing about the basic theory of modal analysis, and briefly summarized several kinds of common damage identification methods;3)Using the most commonly of beams as the research object, and establishes the supported beam with one place, multiple places of damage.Which can identify the damage by ?_m and ?_a indicators. Comparing the identification method about ?_AFCR and MFCD indicators. According to the simulation, it shows that the damage location and degree of structures can be effectively identified by?_AFCR and MFCD indicator, not matter in one place or multiple places of damage cases, which is better than?_AFCR and MFCD indicators. And it has good anti-noise performance and high sensitivity, which can identify the damage of supported beam by the first or the second modal date. It also can accurate pinpoint the damage location, in slight degree of damage. The new indicators obviously have better accuracy and stability;4) Using continuous beam with each cross and bridge bearings finite element model of damage condition are established. Getting modal parameters such as frequency and vibration mode in order to identification. And using two layers of two span frame structure as the research object, respectively construct the finite element model, which includes the one place, multiple places damage. Obtaining the relevant modal data by the finite element software, and analyzed by MATLAB program. Through the numerical simulation give three other methods of recognition effect in this paper. The analysis shows that it is superior other damage indicators.Which only has lower order mode that can effectively identify the position and degree of structure's damage, and has the advantages of small amount of calculation, and it's easy to implement.