Hybrid Steel Girders for Medium-Span Composite Highway Bridges

High-strength steels (with a characteristic yield greater than 355 MPa) provide opportunities to reduce weight and embodied carbon in bridge structures. However, they are typically ten to fifteen percent more expensive than conventional steel grades. This higher unit cost can be offset by reductions in material tonnage and fabrication in certain applications. In medium-span composite highway bridges, where deck depth is governed by slenderness ratios and ultimate limit state criteria, hybrid fabricated beams (combining different steel grades in the flanges and webs) acting compositely with a reinforced concrete deck slab can provide a carbon-effective alternative. This paper evaluates homogeneous S355 girders and S355/S460 hybrid girders in two typical composite highways bridge configurations: two-span (28m each) and three-span (40m, 54m, 40m). This study compares steel quantity, embodied carbon, and cost, while summarising the design methodology for hybrid steel girders in medium-span composite highway bridges.