Quantitative Study Of Damage Identification On City Bridge Based On Strain Modal

The whole high way bridge systems in China have certain damages for poor natural conditions, long history, overload. According to safety and economy, it is quite valuable for development of the city to master the damage information and do corresponding maintenances for these high way bridges in time.This article is associated with one of the projects called An Intellectual Decision Technology for Damage Identification and Maintenance of Highway Bridge in Beijing sponsored by Beijing natural scientific fund. This paper mainly focuses on the study of the application of the ideal damage identification parameter named strain modal. Strain modal is a modal parameter which can reflect the changes of the local characteristic in the structure. It has been proved that strain mode has much more sensitization than mode and frequency on changes of local characteristic. Theoretically speaking, certain crack or damage in structure will result in reduction of stiffness in the local part, and also will result the stress and strain concentration in the same part. These will be represented in strain mode curve diagram which has a peak in the damage part. According to this principle, the structural damage can be identified using the strain modal datas.This paper study on the peak of strain mode curve diagram, and present a method to identify the relative damage extent. Combining the strain mode curve data and element stiffness updating method, this paper present a method to identify the absolute damage extent. At last, the methods of location and damage extent identification have been integrated to a damage identification software which will make the identification conveniently.The studies in this article are as follow:1. Building a more perfect damage study model which using different element type to simulate the concrete and steel bar to replace traditional integral model in the FEM. This model will be more coincidence with the real structure.2. Present the conception and calculate method of blow-up degree of the peak based on the peak of strain mode curve diagram. This conception is used to identify the relative damage extent and got the well effect.3. Present an absolute damage identification method based on strain modal and element stiffness updating.4. Develop a beam damage identification software based on the all achievement of damage identification in this paper. It makes the damage location and degree identification integrate in software which explores a little in the aspects of theory and application.