Keywords: advanced composites, GFRP pultruded profiles, flexural behaviour, local buckling, lateral-torsional buckling.

The durability problems experienced by traditional materials and the need for higher construction speed have fostered the development of new structural solutions. Fibre reinforced polymer (FRP) materials, in general, and glass fibre reinforced polymer (GFRP) pultruded profiles, in particular, have been assuming an increasing role in this domain. In fact, GFRP profiles have great potential as structural materials, presenting several advantages over traditional materials, due to their high strength-to-weight ratio, lightness, electromagnetic transparency, ease of installation, low maintenance requirements and durability under aggressive environments [1]. As drawbacks, in addition to the initial costs of GFRP profiles, that are still not competitive for mainstream applications, there are still no generally accepted design codes or guidelines available for civil engineers. At present, most structural designs are based on manufacturer design guides, mainly presented in a tabular format, which are often incomplete and over conservative [2]. In order to develop design codes, additional research is needed to acquire in-depth understanding on the structural behaviour of GFRP profiles, particularly their failure modes and corresponding ultimate loads.

Part 1 of this two-part paper discusses the results of an experimental investigation carried out at IST on the first-order, buckling and post-buckling behaviour of beams made of GFRP pultruded profiles. Tests were first carried out on small-scale specimens in order to determine the most relevant material mechanical properties. Full-scale tests were then conducted on I-section (i) simply supported beams with spans varying from 1.0 m to 4.0 m under 3-point bending (series S1) and (ii) cantilevers with spans ranging from 2.0 m to 4.0 m subjected to a tip point load applied at either the end cross-section centroid or its top/bottom flange centre (series S2). While the first series is aimed at investigating the flexural behaviour in service and failure conditions (including the local buckling of the top flange), the objective of the second series is to study the collapse behaviour due to lateral-torsional buckling.

The results obtained in the experimental study reported herein show that, due to the GFRP low Young's modulus and high strength, the beam structural integrity is often governed by either excessive deformations and/or local and global buckling phenomena (rather than by material strength limitations). Moreover, the low shear to Young's modulus ratio implies that the role played by the shear deformation is quite relevant, particularly in beams with low slenderness values.

1

J.R. Correia, "GFRP Pultruded Profiles in Civil Engineering: Hybrid Solutions, Bonded Connections and Fire Behaviour", PhD. Thesis, Instituto Superior Técnico, Technical University of Lisbon, 2008.

2

J.R. Correia, "GFRP Pultruded Profiles. Use of GFRP-Concrete Hybrid Beams in Construction", M.A.Sc. Thesis, Instituto Superior Técnico, Technical University of Lisbon, 2004. (in Portuguese)

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