Predicting Flange Local Buckling Capacity of Pultruded GFRP I-Sections Subject to Flexure
Publication: Journal of Composites for Construction
Volume 24, Issue 4
Abstract
Flange local buckling (FLB) of pultruded glass fiber-reinforced polymer (pGFRP) I-sections subject to flexure is investigated in this study. An experimental program, consisting of 62 four-point bending tests that had various constant moment region and shear span lengths, was conducted. It was shown that critical FLB moment capacities increased as the flange slenderness ratios decreased and FLB was the dominant buckling mode for sections that had large flange slenderness ratios. Using classic plate theory and the energy method, an analytical study was carried out and an explicit equation for predicting the critical FLB moments of pGFRP I-sections was proposed. The elastic rotational restraint at the flange–web junction was studied and a modified spring constant, k, was proposed. In addition, the buckling stiffening effect of the test geometry was described through a numerical study. The proposed predictive FLB equation was validated using experimental results from this study and others and was compared with two commonly accepted design guides, Kollár's numeric solution, and finite strip method (FSM) solutions. A good agreement was found between the proposed equation and experimental results and FSM. The proposed equation showed improved predictive accuracy over existing design guides and numeric solutions.
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Acknowledgments
The authors wish to thank Bedford Reinforced Plastics. The second author also thanks the financial support of Conselho Nacional de Desenvolvimento Científico e Tecnológico, through scholarship 201799/2014-6. All tests were conducted in the Watkins-Haggart Structural Engineering Laboratory at the University of Pittsburgh.
Notation
The following symbols are used in this paper:
- b
- flange width;
- c
- constant accounting for deformed shape of plate in cylindrical bending; c = 4 for an I-section subject to flexure;
- ci
- constant coefficient (i = 1 and 2);
- d
- section height;
- Dij
- plate flexural stiffness parameters; Dij (i, j = 1,2 and 6) are given in Eqs. (5)–(8); superscripts indicate flange (f) or web (w);
- EL
- longitudinal modulus of elasticity;
- ELC
- longitudinal compressive modulus of elasticity;
- ELT
- longitudinal tensile modulus of elasticity;
- ET
- transverse modulus of elasticity;
- FLC
- longitudinal compressive strength;
- FLT
- longitudinal tensile strength;
- FT
- transverse strength;
- fcr
- critical buckling strength;
- fx
- uniform compressive stress in the longitudinal direction of the plate;
- GLT
- shear modulus of elasticity;
- k
- spring constant, simulating rotational restraint at flange–web junction;
- L
- half wavelength of the buckled flange plate in the longitudinal direction;
- Lb
- unbraced beam length, length between points that are either braced against lateral displacement of the compression flange or braced against twist of the cross section;
- Lcr
- critical half wavelength of FLB;
- Lprovided
- experimentally observed half wavelength of FLB;
- Mcr
- critical buckling flexural strength;
- n
- observed number of half waves of FLB;
- S
- elastic section modulus about principle axis; S = [bd3 − (b − tw)(d − 2tf)3]/6d for an I-section;
- t
- flange or web thickness, for pGFRP it is typical that tf = tw;
- tf
- flange thickness;
- tw
- web thickness;
- U
- strain energy;
- vLT
- major Poisson's ratio of anisotropic plate;
- vTL
- minor Poisson's ratio of anisotropic plate;
- w
- displacement function;
- W
- potential energy; and
- φ
- material resistance factor.
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Published In
Journal of Composites for Construction
Volume 24 • Issue 4 • August 2020
Copyright
© 2020 American Society of Civil Engineers.
History
Received: Jan 16, 2019
Accepted: Jan 21, 2020
Published online: Apr 24, 2020
Published in print: Aug 1, 2020
Discussion open until: Sep 24, 2020
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