Numerical study of the effect of circular openings in the upper surface of rectangular hollow flange steel beams on the sectional moment capacity

• The reduction ratio of beam capacity with RHF openings is directly proportional to the opening diameter, RHF height, and steel yield stress. • The reduction ratio of beam capacity with RHF openings is inversely proportional to the thickness and width of the RHF and the beam web height. • The compact class has lower reduction ratios than the non-compact and slender classes. • The effect of all variables on reduction ratios is nonlinear, except the steel yield stress which is linear. • Model for predicting the reduction ratio in moment capacity based on opening diameter. Rectangular Hollow Flange (RHF) steel beams may have openings drilled in their top surface to pass some plumbing and electrical wiring inside the RHF cavity. These openings affect the behavior of these steel beams and may reduce their resistance to bending moment. To investigate this effect, Finite Element Modeling (FEM) was used to simulate RHF steel beams with and without flange openings with several variables in geometric dimensions. The FEM results were examined using 8 experimental test specimens of RHF steel beams obtained from previous studies without flange openings. The results showed high accuracy in modeling these RHF steel beams in structural behavior and ultimate bending moment capacity. Current design codes were applied to predict the capacity of these RHF steel beams without flange openings, both from FEM results and experimental tests. The prediction values were always less than the ultimate capacity of RHF steel beams without flange openings. After verifying the results, 98 RHF steel beams with different flange opening diameters were modeled. The reduction ratios in ultimate capacity in steel beams with hollow flange openings are directly proportional to the opening diameter, hollow flange height, and steel yield stress, while they are inversely proportional to the thickness and width of the hollow flange and the steel beam web height. The reduction ratios in the ultimate capacity for RHF steel beams with flange openings are small in the compact category, and these ratios increase with the non-compact and slender categories.