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Developments and new trends in composite truss bridges are reviewed, and recent designs are presented for road and railway bridges. The structural scheme may range from a continuous truss girder to a cable‐stayed bridge with a double deck for both road and rail traffic. Composite decks with 3D tubular triangular trusses for road bridges are discussed; design issues are outlined and some results for the elastoplastic redistribution of internal forces at ULS, based on recent numerical and experimental research studies, are presented. Recent designs of skew semi‐through composite trusses, for High Speed Railway, are reported in what concerns the dynamic behaviour under traffic loading and the stability of the compressed chord. The Base Case Design of a cable‐stayed bridge, 540 m long main span, with a double composite truss deck, for the new railroad crossing of the Tagus River in Lisbon, is discussed.

The use of High Strength Steel (HSS) S690 in highway bridges decks is not yet widespread. A research program investigated the optimal use of HSS S690 within bridges was conducted. A comparative design is presented for a 21.5 m wide highway bridge, with a typical 80 m long span and a composite steel‐concrete twin plate girder deck. Two designs are compared, using the Eurocodes: Design (A) adopted standard S355 NL steel grade whereas Design (B) uses HSS S690 QL or QL1 on the main girders. Comparison between the two designs shows that using S690 enables reductions of 25% on the steel weight and about 65% on full penetration welding volume, compared to design with S355. The deck can be slender using HSS and have thinner plates, but it is more susceptible to local buckling phenomena. Brittle fracture is slightly less dimensioning using HSS, but girders are likely to be much more prone to fatigue, which proves to be the main issue of the design together with the local buckling phenomena. The critical fatigue welded joints are analysed according to EN 1993–1‐9. For plate girders with transverse stiffeners, fatigue presents a major design constraint, namely on span sections, due to allowable plate stresses range near the welded joints. Standard fatigue load model FLM3 with the damage equivalent factor concept is used for fatigue design of several plate girder details. Fatigue resistance of the welded joint between the transverse stiffeners and the bottom tension flange proved to be the most relevant aspect of the design of the composite steel‐concrete twin plate girder deck designed for HSS S690.

The use of High Strength Steel (HSS) S690 in highway bridge decks is not yet widespread. A research program investigated the optimal use of HSS in bridges. A comparative design was performed for a 21.5 m wide highway bridge, with a typical 80 m long inner span and a steel-concrete composite twin plate girder deck, using the Eurocode standards. Three designs were produced: Design (A) with S355 NL steel grade, Design (B) with HSS S690 QL/QL1, and Design (C), also with HSS S690, but exploring different design options provided by welded joint treatments to improve fatigue and suggest possible enhancement of the present Eurocode rules. General guidelines for the design of highway bridge decks using HSS S690 are provided. Keywords: bridges; steel-concrete composite deck; high strength steel; plate buckling; fatigue Hochfester Stahl S690 für Autobahnbrücken -Allgemeine Hinweise für die Bemessung und Konstruktion. Die Verwendung von hochfestem Stahl (HFS) S690 für Autobahnbrücken ist noch nicht weit verbreitet. Ein Forschungsprogramm hat die optimale Verwendung von HFS für Brücken untersucht. Für eine 21,5 m breite Autobahnbrücke mit einer typischen inneren Stützweite von 80 m und einem Stahlbetonüberbau mit zwei Plattenträgern wurde ein Konstruktionsvergleich nach Eurocode erstellt. Es wurden drei Entwürfe Stichworte: Brücken; Stahlbetonüberbau; hochfester Stahl; Blechbeulen; Ermüdung ULS bridge deck design 2.1 Bending resistanceThe flange widths and thickness of the main plate girders were first defined to achieve the required bending resistance. The span flanges were then re-assessed based on fatigue requirements. The final geometry of the main girders is presented in Figures 2 to 7, for standard steel S355 and HSS S690.Differing from the Class 3 sections usually adopted in the design of support sections, when using HSS the bottom flange and web at support sections are Class 4, due to the compact thickness required and the very low value of