Response surface application in vibration-based damaged detection of a railway bridge

Environmental and operational variables and their impact on structural responses have been acknowledged as one of the most important challenges for the application of the ambient vibration-based damage identification in structures. The damage detection procedures may yield poor results, if the impacts of loading and environmental conditions of the structures are not considered. The reference-surface-based method, which is proposed in this paper, is addressed to overcome this problem. In the proposed method, meta-models are used to take into account significant effects of the environmental and operational variables. The use of the approximation models, allows the proposed method to simply handle multiple non-damaged variable effects simultaneously, which for other methods seems to be very complex. The inputs of the meta-model are the multiple non-damaged variables while the output is a damage indicator. The reference-surface-based method diminishes the effect of the non-damaged variables to the vibration based damage detection results. Hence, the structure condition that is assessed by using ambient vibration data at any time would be more reliable. Immediate reliable information regarding the structure condition is required to quickly respond to the event, by means to take necessary actions concerning the future use or further investigation of the structures, for instance shortly after extreme events such as earthquakes. The proposed damage identification method is applied to a numerical finite element model, which is a concrete filled beam bridge that is excited by an ICE train series. The train speed and ambient temperature are chosen as environmental and operational variables respectively. In addition to the natural frequencies, wavelet energy damage indicator is used. The results of the numerical study show that the proposed damage identification method is able to discriminate the damaged and undamaged scenarios of the bridge model. The results also show that the wavelet energy damage indicator is sensitive to small change of structure. However, it does not always have a monotonic trend with respect to damage severity. (C) 2015 Published by Elsevier Ltd.