Optimum Tie Constraint at Screws Spacing in Cold-Formed Steel Built-Up Box Beams Subjected to Four-Point Flexural Loading

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ABSTRAK

Cold-formed steel has many advantages, including high strength, lightweight, fast and practical installation, durability, recyclable, non-combustibility, and simple manufacturing procedures. In general, the open section beams are used widely in roof construction. However, since the shear center and the centroid of the cross-section do not coincide, open-section beams are prone to instability modes. To address this issue, researchers have used doubly symmetric built-up sections or built-up closed sections beams. This study presents an experimental investigation on Cold-Formed Steel (CFS) built-up box beams with varying screw spacing arrangements. Six beam specimens, each with a span of 1300 mm, were subjected to four-point bending tests. The beams were fabricated from C75×35 profiles with a thickness of 0.75 mm, assembled face-to-face into built-up box sections using self-drilling screws positioned along the flanges to act as tie constraint at screws. Three screw spacing configurations were considered—H, 2H, and 5.5H—where H denotes the section depth. All tests were conducted under simple support conditions. Experimental testing was performed using a Universal Testing Machine (UTM) with a displacement-controlled loading rate of 0.5 mm/min. Findings indicate that screw spacing significantly influences the flexural behavior of CFS built-up box beams. Based on the outcomes, a screw spacing of 5.5H is recommended for design applications under four-point bending conditions.

Kata kunci: tie constraint at screws spacing, cold-formed steel, built-up box beams, experiment