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Received Oct 5, 2017; Accepted Dec 28, 2017
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1. Introduction
Infrastructures, such as bridges, play an important role in city life and are exposed to various kinds of excitation during their operational life. Structural Health Monitoring (SHM) is a tool to control safety and detect possible damage from structural responses. In some cases, it is impossible to measure the operational load exerted on a bridge, for example, under heavy traffic [1]. In such cases, where a complete knowledge of excitation is not available, output-only modal identification and damage detection methods can be used.
Obtaining a structural vibration response by an accelerometer is one of the easiest and cheapest approaches to SHM. Accelerometers are easy to install at virtually every point along the structure and can provide time-history acceleration data at a wide range of sampling frequencies. Using accelerometers in damage detection methods reduces the cost of SHM significantly.
Acceleration data contain responses of all frequencies and show singularities when damage occurs. Such singularities in acceleration signals cannot be observed by the naked eye. Several researchers dealt with the acceleration data to find these singularities using different methods, such as wavelet-based methods [2–5], Random Decrement Technique (RDT) [1, 6–9], and Blind Source Separation (BSS) methods [10–14].
Hester and González [2], Balafas and Kiremidjian [3], and Cantero and Basu [4] worked on wavelet transform analysis to find damage and singularities from acceleration signals. The wavelet transform output-only method exhibits large potentials for detecting singularities and damage to structures and bridges and can easily identify the damage with a delta value of 0.1 (where delta refers to the ratio of the crack height to the member height) in a noise-free dataset. Hester and González [5] showed that the impact of the road profile can generate a significant error, affecting structural damage results identified by the wavelet-based methods.
Introduced by Cole in 1968, RDT is one of the most promising output-only techniques when the controlled or initial excitation cannot be measured. RDT is a special averaging method to obtain the free response from output-only data [15]. Further, Ibrahim et...