Damage Statistics Recognition Method Based On Strain Modal For Continuous Bridge

With rapid development of the modern transportation, more and more requirements are taken out due to safety and utility of bridges. It is of urgent demand to accurately find out damage of bridges and their components in time. After years since its being run, bridge is always vulnerable because of bad environments and poor management for structural element performance. Once a bridge loses its function, especially to a key bridge, a paralysis of traffic seriously direct and indirect economic losses will be brought. Therefore, it is very necessary to set up a system to servicing real-time healthy detection, damage identification and health diagnosis for a bridge.Nowadays, physical change of structural response information such as strain and displacement mode shape has been widely utilized in health diagnosis problems and monitoring those parameters is getting more and more attention to ensure the structural integrity. Strain mode is a modal parameter that can response the changes of the local characteristic of the structure. It has been proved that strain mode has much more sensitization than frequency to reflect local structural variable characteristics, especially to continuous bridges. Therefore, in this thesis, the peak of strain mode curve diagram is used to locate damages. Then, finite element analysis is applied to formulate a quantitative damage extent analysis method and a checking test for this method is done to prove the method is feasible.Many structural parameters change at random, difficult to define exactly. In addition, when certainty identification mehod is introduced to identify damage in a sample, measurement noise affects so great as not to eliminate. Therefore, statistical modal analysis method is adopted for minishing negative effects of measurement noise, and in order to assess the state of global health of bridge structures using the modal parameters with many uncertainties, hypothesis test theory is adopted herein. At the same time, the thesis uses the tatistic method. It not only clears up negative effects of measurement noise, but also digs out difference between structure parameter probability density functions before damage and after damage, estimate whether the structure amages statistically.The thesis combines finite element method, modal strain energy of change, and statistic method, develops a sort of damage statistic identification method. What is more, the thesis proves validity of the method from theory.In order to prove that damage statistic identification can be done by use of the proposed methods, a finite element model of a real continuous bridge structure for simulated damage location and damage extent bases on ANSYS and MATLAB software is set up to test feasibility of the proposal method. The result shows that the proposal methods are correct, reliable and suitable for engineering application.At last, the main contributions and conclusions of the thesis are summarized, and some further research topics concerning are brought forward.