This study discusses the size and distance optimization of hexagonal holes in castellated steel beams. The optimization study of castellated steel beams was performed using finite element method (FEM). The results of optimization analysis are then verified by implementing laboratory tested of 225 mm height castellated steel beam specimens. The specimens were modified from 150 mm height IWF section profile. The model of castellated steel beams is divided into six different variation models which represent 45̊, 50̊, 55̊, 60̊, 65̊ and 70̊ opening angle of hexagonal holes. All castellated steel beam models have 150 mm vertical height holes (ho) and each holes are separated with equal distance varies from 0.042ho to 3.153ho. The results of FEM analysis indicate that the strength of castellated steel beams increase with a factor of 1.938 to 2.041 compare to 150 mm IWF original profile. The optimum results from FEM analysis was a castellated steel beam that has 60̊ angle size with the optimum hole distance was 0.186ho to 0.266ho. Comparison analysis of laboratory test results and FEM analysis results indicated that the difference between those two approaches are not more than 1.011 with COV (coefficient of variation) value 0.069.
