Typical Deck Sections and Applications

Orthotropic steel decks are typically classified as either open-rib or closed-rib systems. In either case, the ribs are arranged in the longitudinal direction of the bridge and distribute wheel loads to the intermediate floor beams, while also providing increased flexural stiffness to the primary structural component. The ribs are rarely orientated in the transverse direction, as this orientation can cause problems with the durability of the wearing surface (19). The longitudinal ribs are typically made continuous through openings in the web plates of the floor beams. Closed-ribs are typically used in orthotropic steel decks that are subjected to direct wheel loads.

As shown in Figure 15, open-ribs are usually made from flat bars, bulb shapes, inverted teesections, or angles. Open-ribs are not necessarily ideal for use in decks subjected to wheel loads. Open-ribs do not have the torsional stiffness to efficiently distribute transverse loads to adjacent ribs, resulting in more ribs and closer floor beam spacing as compared to a closed-rib system. Open-ribs are more often used to stiffen box girder webs and bottom flanges.

Closed-ribs are typically made from trapezoidal, U-shaped, or V-shaped sections, as shown in Figure 15. Trapezoidal rib sections are the most common specified in orthotropic steel decks. Closed-ribs have a much higher torsional stiffness than open-ribs, and thus closed-ribs better distribute transverse loads to adjacent ribs. The closed-rib system is complicated by the partial penetration weld on the outside of the closed-rib where it attaches to the deck plate, and is a fatigue sensitive detail that requires care to execute with consistent quality. Furthermore, due to the torsional rigidity of the closed-rib, decks using closed ribs are subjected to secondary deformations and stresses that must be addressed in design.

Advantages of orthotropic steel decks are realized in long span bridges because the deck is lightweight (typically 60% of comparable concrete) and can be made composite with the main longitudinal girders. As such, orthotropic bridge cross sections are good candidates for suspended span bridges such as suspension, cable-stayed, and tied arch bridges, minimizing the dead load on the entire bridge system. Cross sections have included plate girders with orthotropic steel decks, as well as multi-cell box girders, single-cell box girders, and combinations of stiffening trusses and floor beams.

Orthotropic steel decks are also effective in movable bridges because of their reduced weight as compared to conventional reinforced concrete deck slabs. The reduced weight of the deck also results in a reduction in the size of the counterweights required. Also, a movable bridge with an orthotropic steel deck requires less power from moving devices, and reduces the internal forces in the trunnions.

I-girder bridges in the short to medium span range can also utilize orthotropic steel decks, because of their internal redundancy and possibly eliminating the potential for complete future deck replacement. Orthotropic construction is often found in box girder sections, as slender plate components requiring stiffening. Steel box girders utilizing an orthotropic deck result in a lighter superstructure, which allows for modular construction techniques.