Experimental Investigation of the Structural Behavior of Steel–Concrete Composite Beams with Circular Web Openings

This study experimentally investigates the structural behavior of steel–concrete composite beams with circular web openings under monotonic loading to evaluate the effects of opening location and number on structural performance while maintaining feasibility for integrating mechanical, electrical, and plumbing (M.E.P.) systems. Six simply supported composite beam specimens were tested, including one reference beam without openings and five beams with 80 mm diameter circular web openings. The investigated variables were limited to the presence, number, and longitudinal location of the openings, while the beam dimensions (IPE160 section, 2.8 m clear span), material properties, reinforcement details, shear connector arrangement, and loading conditions were kept constant. The study addresses a specific research gap: Previous studies have primarily focused on the effects of opening number and size on ultimate load capacity, with limited systematic investigation of how opening location influences not only ultimate load but also stiffness and ductility. Openings were strategically placed in three critical zones: the shear zone (low stress region), the bending zone (high moment region at mid-span), and the region under load points. The experimental results demonstrated that opening location is more critical than opening number. Openings in the shear zone achieved the best performance with only 2.13% reduction in ultimate load capacity, making it the preferred location for service openings. Openings in the bending zone (mid-span) or under load points caused reductions ranging from 9.62% to 11.70%, attributed to interference with high bending stresses. Notably, the configuration with ten openings achieved a load reduction similar to the two-opening configurations when located in the shear zone, confirming the dominant role of location over opening number within the experimental program. These results support a location-driven design philosophy for composite beams with web openings. However, these findings are restricted to the present experimental configuration—specifically 80 mm circular openings, IPE160 steel section, 2.8 m clear span, and the tested loading condition—and should not be generalized to composite beams with different geometric parameters, material properties, or loading conditions without additional research.