A Simplified Design Method for Lateral–Torsional Buckling of GFRP Pultruded I-Beams


This paper provides a simplified design approach for estimating the lateral–torsional buckling (LTB) strength of the pultruded glass fiber-reinforced polymer (GFRP) composite I-beams. A detailed finite element (FE) model based on ABAQUS incorporating more realistic parameters for pultruded GFRP I-beam is developed and verified against the test results available in the relevant literature. After achieving a reliable FE model (through high degree of accuracy in the numerical validation), detailed parametric studies were undertaken by varying the section geometries as well as the span of pultruded I-beams. The selection of the sectional dimensions was based on the composite manuals available in the market, to ensure ease in the practical application of the outcomes of this study. In this analysis, simply supported beam with a uniform bending moment is considered. In accordance with the results of the FE parametric analysis, the accuracy of the theoretical LTB strengths predicted by the equations proposed for pultruded GFRP beams available in the literature is assessed. This comparison indicates that the existing method results in an over-conservative LTB strength estimates for pultruded GFRP I-beams, especially in the low and medium slenderness range. This is primarily due to a comparatively lesser impact of section imperfections on LTB resistance than high slenderness range. Therefore, to address this shortcoming, new simplified design formulations were proposed to have high accuracy of the LTB strength predictions for pultruded GFRP I-beams especially in the low and medium slenderness range. The proposed equations have been provided that might aid the structural engineers in economically designing the pultruded GFRP I-beams in the future.

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L :

Beam length

B :

Flange width


Section depth

T 2 :

Web thickness

T 1 :

Flange thickness

R :

Root radius

χ LT :

Reduction factor

\(\overline{\lambda}_{{\text{LT,0}}}\) :

Plateau length

\(\overline{\lambda }_{{{\text{LT}}}}\) :

Non-dimensional slenderness

\(\alpha_{{\text{LT}}}\) :

Imperfection factor

σ loc :

Local buckling stress

\(\gamma_{{\text{M1}}}\) :

Safety partial factor

\(W_{\text{x}}\) :

Section modulus about the major axis

M LT :

Lateral–torsional buckling moment

M cr :

Elastic critical lateral–torsional buckling moment

M crl :

Elastic critical local buckling moment

υ LT :

Lamina major Poisson’s ratio

M Ng :

LTB moment predicted according to Nguyen et al. curve

M Prop1.:

LTB moment predicted according to design option 1

M Prop2.:

LTB moment predicted according to design option 2

P cr, FEA :

Lateral–torsional buckling load

E L , E T , G LT :

Longitudinal, transverse and shear modulus of elasticity


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Correspondence to M. Anbarasu.

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Anbarasu, M., Kasiviswanathan, M. A Simplified Design Method for Lateral–Torsional Buckling of GFRP Pultruded I-Beams. Arab J Sci Eng (2021). https://doi.org/10.1007/s13369-020-05208-9

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  • Fiber-reinforced plastic composites
  • FRP beams
  • Glass fiber composite
  • I-beams
  • Lateral–torsional buckling
  • Numerical analysis
  • Pultruded profile