Numerical investigation on the stabilisation of a built-up composite beam by trapezoidal sheeting during the construction stage

This paper investigates the construction-stage stability of a novel composite parking beam with a built-up cross-section, formed by welding a half-castellated IPEo 300 section onto an HEAA 340 section. The beam is designed for multi-story car park structures with a span of 15.75 m and a bay spacing of 5.0 m. During the construction stage, the slender built-up section is susceptible to lateral torsional buckling (LTB) and lateral distortional buckling (LDB). To stabilise the beam, the trapezoidal sheeting is connected to both the middle and top flanges via a closure plate, without requiring purpose-built stabilisation elements beyond the standard floor construction components. Since existing simplified Eurocode methods are not directly applicable to this non-standard cross-section and connection configuration, a geometrically and materially nonlinear analysis with imperfections (GMNIA) following EN 1993-1-14 is adopted as the verification framework. The material properties and fastener behaviour are characterised experimentally through tensile coupon tests and lap-shear component tests. The numerical modelling methodology is validated against experimental shear diaphragm tests from the literature. Results show that without stabilisation, LTB reduces the beam capacity to 15% of the design load. With the closure plate connection, the capacity increases sevenfold, and all configurations investigated in a parametric study, covering imperfection amplitudes from L/1000 to L/150, fastener stiffnesses from 60% to 120% of mean experimental values, and sheeting thicknesses from 1.00 to 1.25 mm, exceed the design load with a worst-case utilisation ratio of 0.980. The insensitivity of the results to all three parameters confirms that the stabilised beam operates in the plateau region of the buckling curve, where plastic resistance governs.