A closed-form equation for the local buckling moment of pultruded FRP I-beams in major-axis bending

A new closed-form equation for the local instability of pultruded fiber-reinforced plastic beams in bending is derived by substituting suitable buckling approximating functions for compression flange and web into the total potential energy functional. Being obtained from a full-section approach, the equation does not require independent calculations for web and compression flange, which are typical of discrete plate analysis. Moreover, the contribution of the elastic restraint stiffness commonly used to reproduce the web–flange junction behavior naturally arises in the proposed formulation because of the assumed buckling shape. From comparisons with available experiments on 10 beams and FE solutions for 55 beams, the proposed equation appears to be accurate and reliable.