Influence of Openings and U-section Height Variation on the Structural ‎Behavior of Steel-concrete Composite Beams Containing Openings

Abstract

This study investigates the experimental effect of openings and varying steel section heights on the structural ‎behavior of concrete-filled cold-formed U-shaped composite beams. Four specimens were fabricated and ‎tested under four-point loading: one reference beam without openings (CB1) and three with circular openings ‎at different section heights (300, 350, and 400 mm). The results showed a 16% reduction in the ultimate ‎flexural strength with openings compared to the reference beam, with a significant increase in deflection and ‎slippage due to the loss of effective section area and the formation of stress concentrations around the ‎openings. Increasing section height, on the other hand, gradually improved strength and stiffness, with the ‎ultimate load reaching 305 kN at a height of 400 mm, indicating the ability of the larger section to ‎redistribute stresses and reduce slippage. The specimens also demonstrated a transition in failure mode from ‎localized failure around the openings to a more uniform flexural failure at higher heights. These results ‎emphasize the importance of incorporating geometric considerations of openings and height into the design ‎to ensure efficient performance and safety of modern composite beams.‎