Study On Damage Identification Of 100 Meters All Welded Steel Trestle

With the rapid development of port logistics in China, trestle structures, as maritime port facilities, enter a period of rapid growth, and the number of new and old trestles has been increasing. At present there are plenty of domestic and foreign researches on health monitoring of bridge structures, however, most of the researches have focused on ordinary bridges under vehicle loads for land traffic connection. There is little study on steel trestle structure like the trestle of oil dock in Dalian New Port which plays a special role. Therefore, the study of damage identification and health monitoring on this type of bridges will not only fill the academic blank, but also will guarantee the safe use of the steel trestles and ensure the safety of national people's lives and property.The trestle of oil dock in Dalian New Port is chosen as the engineering background, and its finite element numerical model has been established in this paper. By discounting the flexural rigidity of the element material, the damage identification of the steel trestle's bottom chord beams on both sides has been studied on various damage cases. The contents of the research are as follows:(1) According to the previous research achievements of modal curvature, normalized average absolute difference of modal curvature damage indicator has been presented. Using the numerical simulation modal data of the steel trestle's bottom chord beams before and after the damage, the study of damage identification is carried out under three kinds of damage cases in this paper, one element or more elements have damaged on either bottom chord beam and both bottom chord beams have damaged. It proves the damage indicator is effective to locate the damage element.(2) The Modal Flexibility Difference Curvature and the Modal Flexibility Curvature Difference damage identification indicators are based on flexibility matrix method. The two indicators'damage identification effects to the bottom chord beams of the steel trestle are studied in this paper. It proves that the damage identification results of the two damage identification indicators wouldn't be affected by other elements'damage cases when several elements of either bottom chord beam or both bottom chord beams'elements have damaged. According to the values of these two indicators under the damage case of only one element has damaged, we can judge the damage elements'location and their damage degree under other damage cases. (3) We can obtain the acceleration time-history response signal of the bottom chord beam after the application of a excitation loading on its middle, and then decompose the acceleration signal by wavelet packet method. The damage detection of the bottom chord beam has been researched using the signal components energy curvature difference as the damage identification indicator. It proved that this damage indicator can identify every damage element no matter what damage cases happened.The research results show that the three damage identification indicators are effective to locate damage elements for the steel trestle's bottom chord beams; where the location of a damage element will not be influenced by other damage elements in the same bottom chord beam; one bottom chord beam's damage has no effect to the other one. Modal flexibility difference curvature, modal flexibility curvature difference and wavelet packet signal components energy curvature difference, these three damage indicators even can be used to detect damage degree under any damage cases. All the conclusions can provide a reference for engineering detection.