FEM Updating And Structure Damage Detection Method Research

A precise structural dynamic modal is very important to forcast the structure response.Since the Finite Element Model( FEM) updating technolygy produced, it has caused great attention and improved rapidly. Now this method is used in aircraft and civil engineering widely.Because of the difference between the numerical modal calculation and the measurement date, we get a different dynamic result . To compare the numerical modal calculation result and measurement date, we need to updating the FEM. Although the measurement date is not a precise result, sometimes we take the measurement date as a standard date. The next step is how to updating the FEM to get a result that is close to the measurement date. This is the basic meaning of FEM updating.This paper do some research about FEM updating and structure damage detection. FEM updating method can be divided into two groups, one is updating the FEM model, the classic method is Berman and Baruch method; another is modify the design parameter directly, for example E, A. This thesis illustrate several FEM updating methods. As to Berman method, give a numerical example, proved that Berman method have the advantage of high precise, easily operation.As an important apply of FEM updating, at last, this paper introduced a damage detection and health monitor meathod .Structure health monitor and damage detection is a new scientific technology, widely used in bridge structure.Now many methods are used in damage detection and health monitor. In this thesis, mainly introduce a method named : a damage detection method based on strain measurement under dead load. This technology can detect the damage rapidly. This method consider that under dead load , after damage, the iner force redistributed and strains changed on structure. We can location the damage and know the damage degree through the strains varaiblity. This meathod has two advantages, one is only need static strains measurement, compared to dynamic response measurement, it is more convenient, reliable, simplified the data collection and deposite treatment procedure; another is excitement only consider the self weight, simplified the expensive and complex loading procedure. This paper establish a anlytical model for simple beam, one end is fix, one end is simple. The strains expressed with the damage parameter such as a,α,δ,so, we can get strains condition on the beam, when the model damage under damage parameter close to the real damage condition, the difference between the experimental strains and the model strains minimized. With the optimizing method, we can get the best a,α,δ. When this method applied in frame structure, only define two damage parameter, damage location ie element number i, damage degree α. The main load on most civil structure is dead load if not consider the earthquack force and wind force, in most condition the live load effection is less than that of dead load. So, this meathod may be widely used in civil structure damage detection.