AbstractThis paper proposes, for the first time, a design methodology against the web-crippling failure of pultruded glass fiber–reinforced polymer (GFRP) I-section beams, based on the direct strength method (DSM). This study took into consideration previous experimental and numerical data reported by the authors to calibrate the DSM expression. Approximate formulas were derived to estimate the web-buckling and web-crushing loads for beams under end two flange (ETF) and interior two flange (ITF) loading cases. Finite-element (FE) analyses were also performed to generate complementary data, particularly for higher levels of slenderness, providing a more robust basis for the calibration of the proposed design formulations. Both experimental and numerical results were very well approximated by unified DSM expressions, that fitted both ETF and ITF configurations simultaneously, for a significant variety of materials and section dimensions. Finally, the proposed DSM formula also provides an in-depth and important novelty by identifying the slenderness ranges for which the web-crippling failure is triggered by web crushing, web buckling, or an interaction thereof.