Numerical Investigation on the Influence of Shear Lag on Flange Buckling strength of Fiber Reinforced Polymer (FRP) Box Beams

KASIVISWANATHAN, M; Upadhyay, Akhil

doi:10.22059/ceij.2026.393103.2290

Numerical Investigation on the Influence of Shear Lag on Flange Buckling strength of Fiber Reinforced Polymer (FRP) Box Beams

Articles in Press

Authors

M KASIVISWANATHAN ¹

Akhil Upadhyay ²

¹ Civil Engineering department, Sona College of Technology, Salem, India

² Department of Civil Engineering, Indian Institute of Technology Roorkee, Roorkee 247667, India

10.22059/ceij.2026.393103.2290

Abstract

The combination of fiber reinforced polymer composite and box-beam is ideal for light weight bridges but being a thin-walled structure, their designs are often governed by buckling criteria. In the FRP box beam, two types of local bucklings are possible i.e. flange and web buckling. In the wide flange box-beam, flange buckling strength is mainly affected by shear lag phenomenon and it becomes more significant in FRP box-beam due to their quasi-brittle material behaviour. Hence, an attempt is made to understand the effect of shear lag on flange buckling strength of FRP box beams. Firstly, the influence of rotational restraint and moment gradient is desensitized by choosing an appropriate geometry and loading conditions. Similarly, influence of (b/t)f is isolated by using percentage difference in buckling coefficient by comparing finite element (FE) analysis and closed form equation results. Secondly, parametric study based on the linear elastic buckling analysis is conducted to quantify the influence of shear lag on flange buckling coefficient. Finally, based on the numerical results thus obtained and shear lag parameters (ω1,mod and k1), generic curves as well as classes having different range of % increase in buckling coefficient are presented which will be more helpful to the designers.

Keywords

FE analysis

Stability problem

fiber reinforced polymer box-beam

Flange buckling

Shear lag

Subjects