Research Article EEMD-MUSIC-Based Analysis for Natural Frequencies Identification of Structures Using Artificial and Natural Excitations David Camarena-Martinez, 1 Juan P. Amezquita-Sanchez, 1 Martin Valtierra-Rodriguez, 1 Rene J. Romero-Troncoso, 2 Roque A. Osornio-Rios, 1 and Arturo Garcia-Perez 2 1 HSPdigital-CA Mecatronica, Facultad de Ingenieria, Universidad Autonoma de Queretaro, Campus San Juan del Rio, Rio Moctezuma 249, 76807 San Juan del Rio, QRO, Mexico 2 HSPdigital-CA Telematica, Procesamiento Digital de Se˜ nales, DICIS, Universidad de Guanajuato, Carr. Salamanca-Valle km 3.5+1.8, Palo Blanco, 36700 Salamanca, GTO, Mexico Correspondence should be addressed to Arturo Garcia-Perez; agarcia@hspdigital.org Received 12 October 2013; Accepted 22 December 2013; Published 10 February 2014 Academic Editors: S. Berretti and V. Ponomaryov Copyright © 2014 David Camarena-Martinez et al. Tis is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Tis paper presents a new EEMD-MUSIC- (ensemble empirical mode decomposition-multiple signal classifcation-) based methodology to identify modal frequencies in structures ranging from free and ambient vibration signals produced by artifcial and natural excitations and also considering several factors as nonstationary efects, close modal frequencies, and noisy environments, which are common situations where several techniques reported in literature fail. Te EEMD and MUSIC methods are used to decompose the vibration signal into a set of IMFs (intrinsic mode functions) and to identify the natural frequencies of a structure, respectively. Te efectiveness of the proposed methodology has been validated and tested with synthetic signals and under real operating conditions. Te experiments are focused on extracting the natural frequencies of a truss-type scaled structure and of a bridge used for both highway trafc and pedestrians. Results show the proposed methodology as a suitable solution for natural frequencies identifcation of structures from free and ambient vibration signals. 1. Introduction Nowadays, the vibration-based structural health monitoring (SHM) is a major and fast growing research discipline for several felds such as mechanical engineering, aeronautics, and civil engineering, among others, because it allows the examination of the dynamic characteristics of a specifc struc- ture. Te basic idea in vibration-based SHM is that physical variations in the structure change its modal parameters and, consequently, its vibration response also experiments distur- bances. Terefore, accurate identifcation and measurement of modal parameters such as natural frequencies are funda- mental in vibration-based SHM in order to estimate diferent structural conditions [1, 2]. Moreover, a correct identifcation of modal parameters allows building a proper analytical model, as well as determining the existence and location of structural damage, and in some cases calculating the lifetime of the structure [3]. Several vibration excitation sources have been used to excite civil structures in order to measure their modal properties, which can be classifed into two groups. Te frst one named artifcial excitation uses mechanical shakers, drop weights, shoot rockets, control devices, and so on. Te second group, named natural excitation, uses ambi- ent vibrations such as wind and earthquakes. Te ambient vibration testing has the advantage of being inexpensive and not interrupting the normal operation since no excitation equipment and trafc interruption are needed and also has potentials for implementing real-time condition assessment [4–6]. However, the modal parameter identifcation of civil engineering structures using the feld ambient vibration Hindawi Publishing Corporation e Scientific World Journal Volume 2014, Article ID 587671, 12 pages http://dx.doi.org/10.1155/2014/587671