Damage assessment of GFRP pultruded structural elements Salvatore Russo Structural Engineering, IUAV University of Venice, Dorsoduro 2206, 30123 Venice, Italy article info Article history: Available online xxxx Keywords: GFRP profiles Finite element updating Assessment Damage identification Modal analysis abstract This study shows a procedure for the identification of the mechanical characteristics and dynamic param- eters of glass fiber-reinforced polymer (FRP) pultruded elements. The matching between analytical model and experimentally acquired modal and natural frequency data is used to investigate the homogeneity of materials (resin and fibers) and the mechanical characteristics variation for pultruded profile with differ- ent cross sections, also in presence of induced damage. The experimental results are given primacy, and then the model must be modified by trial and error methodologies of model updating approach. This work depicts the sensitivity analysis based FE model updating procedure and its application to mechan- ical characteristics and damage assessment of different GFRP members from modal parameters. The accu- racy analysis, that relies upon the relative confidence between the results (exp. and analytical) features a FE model of pultruded composite profiles with orthotropic behavior. The same structures were subjected to damage and their identification is based on dynamic response through the curvature mode shapes. This approach allows to know the location and size of damage, the change in dynamic characteristics and thus the decrease in strength and stiffness. The damage identification was carried out also with FE analysis by updating the undamaged beam model. Ó 2012 Elsevier Ltd. All rights reserved. 1. Introduction The use of glass fiber reinforced polymer materials, named GFRP, has increased by now in the last years, even in civil engineering [1–5]. Besides, the adoption of specific approaches to design and construction of all-FRP structures [6] introduces the application of new techniques of mechanical behavior analysis of new materials and structures. Many researchers have been addressed on the static behaviour of the profiles [7–9]; while more deepening is needed in the assessment field, this is the reason why this research deals with the check of the stiffness parameters, particularly the damage and imperfection detection on GFRP materials through dynamic tests. In fact, concerning the study of dynamic response of GFRP elements from experimental and analytical point of view, several researches and results have been elaborated [10–13]. In particular, Qiao et al. [14] proposed a study on a pultruded composite cantile- ver I-beam to characterize the dynamic response. The combined analytical and experimental approach of Turvey et al. [15,16] is adopted to determine the dynamic behavior of square and circular pultruded GRP (glass reinforced plastic) plates with central cutouts. A preliminary study of some results analyzed in this research is included in Boscato and Russo [17] and in Boscato [18]. A further research on a free vibration response of a large PFRP cross section is investigated in Boscato et al. [19]. Some authors have investigated dynamic response through micromechanics analysis, with particular reference to basic materials such as the matrix, the fiber reinforcement and the fiber/matrix interface [20]. Gibson and Plunkett [21] have studied the dependence of the mechanical characteristics on the variation of the vibration frequency on a unidirectional composite laminate. In the author’s opinion, the issue here proposed is particularly interesting to complete the matter of reliability of this material, also with reference to the potential application of GFRP structural elements in seismic engineering. As regards models for natural fre- quency analysis of pultruded FRP elements, the currently available literature gives prominence to Timoshenko’s shear-deformable beam theory [22] for isotropic beams, rather than to Euler–Bernoulli’s beam theory, since the latter neglects the effects of transverse shear deformations and torsional stiffness. Starting from Timoshenko’s beam model, further research was developed by Huang [23]. The present study shows the dynamic characteristics such as frequency response and modal parameters of the damaged profiles previously analyzed in their healthy state. The literature related to damage detection in different structure typologies of traditional materials and historic structures [24,25] is funded on the assump- tion that damage can produce changes in mode shapes [26,27]; this theory is assumed as a non-destructive method for identifying and quantifying the present damage and imperfections. However, some studies on the identification through modal parameters have been shown that the variations in frequency and in some mode shapes are unaffected by the presence of damage, but particularly influ- enced by the temperature and environmental condition [28–30]. 0263-8223/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.compstruct.2012.09.014 E-mail address: russo@iuav.it Composite Structures xxx (2012) xxx–xxx Contents lists available at SciVerse ScienceDirect Composite Structures journal homepage: www.elsevier.com/locate/compstruct Please cite this article in press as: Russo S. Damage assessment of GFRP pultruded structural elements. Compos Struct (2012), http://dx.doi.org/10.1016/ j.compstruct.2012.09.014