Detection of damage location in concrete deck of bridge using modified modal strain energy method

One way to diagnose damage in structures is to use their modal strain energy change index. Since occurrence of damage in parts of a structure, in addition to changing the modal strain energy of the damaged parts, also changes the modal strain energy of the healthy parts, in the vicinity of the main damaged elements, false damaged elements will appear, which makes it difficult to identify the main damaged elements. To solve this problem, in the present work a two-step method has been used to determine the location of the damage on the deck of a concrete bridge. In the first step, by finite element modelling and performing the modal analysis, the initial damage index of different parts of the bridge deck is determined based on modal strain energy changes, using a few vibration mode shapes. In the second step, using weight coefficients, the modified damage index for each element is calculated separately, minimizing the number of false damaged elements. The proposed method for calculating weight coefficients is simple and at the same time accurate. The efficiency of this method was investigated in several damage scenarios with an intensity of only 5% in different parts of the deck of bridge. The results showed that, while the initial damage index could not distinguish even 3 damaged elements in the bridge deck from the healthy elements, the modified damage index was able to identify up to 7 damaged elements in different parts of the bridge deck with good accuracy using only 2 mode shapes.