Bridge Damage Detection Methods Based On The Second Order Difference Of Influence Lines

At present, the damage detection of bridges is one of the research focuses in structural engineering. Focusing on beam bridges and considering the general approach in inverse problems,'Make every effort to increase the useful information effectively and reduce the dimensions of damage detection'is treated as guidance in the present study. At first, the types and characteristics of damages which may occur on bridges are analyzed. The criterions of ideal damage detection index are then proposed. Research is carried out step by step from local index (static strain), semi-local index (static difference curvature) to global index. The static strain and difference curvature indices are studied in detail and then it is found that'global index plus mobile load'can be treated as an effective pattern for establishing more proper damage detection index.Further, based on two global indices (support reaction and local point displacement), the idea of'influence line second order difference'is introduced. Three novel indices termed as'Difference Index of Influence Lines for Support Reaction, DIILSR','Difference Index of Influence Lines for Mid-span Displacement, DIILMSD'and'Difference Index of Influence Lines for Displacement at Symmetrical Points, DIILDSP'are then developed, respectively. The philosophy of these new methods is different from the existing damage detection methods. They use the concept of"virtual mashing"to divide the whole bridge into a number of segments with the same length. Therefore, not determining the exact damage location but detecting which segments contain damage is the work needed to be done. The number of unknown parameters which have to be solved is decreased. With the help of this concept, the localization and quantitative analysis of damage can be achieved more effectively. Besides, mobile load is employed to relate the local location of bridge with index values. Therefore, the number of measurement points will not affect the effect of these methods.The algorithm of these new methods is stable and their effect can be adjusted freely by changing the load value and the segment length. Better effect can be achieved with the increase of load value and the decrease of segment length. During the application process, simple measurement, convenient loading and low cost are advantages of new methods. These advantages are further highlighted when the bridge size increases and the number of offered sensors decreases. Moreover, based on the'difference value'concept, these new methods can be applied to the actual bridges with non-homogeneous material/section parameters and unclearly defined support conditions.In addition, in order to satisfy the requirements of damage detection, innovative devices have also been designed to improve the durability of embedded optical fiber strain sensors and the acquisition of displacement data with high precision etc., which are all introduced in detail in the present thesis. These devices have been patented by National Intellectual Property Bureau.Finally, an integrated bridge damage detection scheme which has low cost and well effect for beam bridges is proposed to show the application value of this study.