Abstract Vierendeel failure of castellated steel beams (CSBs) with fillet corner web openings is investigated by the Finite Element Method. Compared to beams with circular openings, CSBs with the proposed fillet corner web openings need only one cut along the web centerline. Therefore the fabrication cost can be reduced. Effects of opening dimensions and opening shapes on the Vierendeel failure of web-perforated members are investigated in this paper. Numerical results indicate that CSBs with the proposed fillet corner web openings enjoy a higher load bearing capacity than those with traditional rectangular or hexagonal openings on condition that they have the same opening height. The M – V interaction method for predicting the load bearing capacity of CSBs with fillet corner web openings is proposed. Predictions obtained from the proposed M – V interaction equation agree well with numerical results.