Steel Orthotropic Decks

The vast majority of the world’s bridges with record-long spans have utilized orthotropic steel deck systems as their superstructures. Even though these types of decks have been used extensively in Europe, Asia and South America, the concept has not yet fully been accepted in the United States. With the trend towards accelerated bridge construction practices with an overall longer bridge life, the steel orthotropic deck presents a viable economical solution.

Rib-to-Deck Joint in Orthotropic Steel Bridge Deck. Photo credit ASCE

Since the decks are designed integral with the girders as a common flange, tremendous weight savings can be realized when designing these components. This method has a complete steel superstructure, offering the potential for a long service life. The other leading benefits of this bridge decking system are the minimization of dead load in the design and the rapid construction that will lessen the impact on traffic.

There are some bridges with steel orthotropic decks that have never experienced fatigue cracking in the weld connections, such as the 1973 Fremont Tied Arch Bridge in Portland, Oregon. Other examples include the Battle Creek Bridge in Salem, Oregon and the Ulatis Creek Interstate I-80 Freeway Bridge in Vacaville, California. Welding details are being developed for AASHTO to achieve bridge life spans of 100 years or longer. By their nature, steel orthotropic decks are inherently redundant in their design, with features like blast resistance and bridge hardening. The San Mateo Hayward orthotropic steel deck uses 3/4″ deck plate or 5/8″ deck plate with open or flat plate ribs. The original wearing surface installed in October 1967 is still in use – that’s 48 years of service life!

Steel orthotropic decks can either be integral with the main girders or be a decking system supporting the steel superstructure. An important advantage is that a short span steel bridge with orthotropic steel deck can be installed as a single component.

The multiple elements that make up steel orthotropic deck systems are fabricated off-site to make bridge deck modules that can be assembled and field-welded at the bridge site. The sections are light enough to place safely with a single crane. Orthotropic steel decks are used for pedestrian bridges and truck weigh scales for rapid single-piece construction.

Several European countries are successfully using steel orthotropic decks. In Russia, a flat plate is utilized in modular steel bridge design, and more than 500 bridges have been constructed. More than 1,000 orthotropic steel deck railroad bridges exist in Europe, with most utilizing flat-plate orthotropic ribs.

In the United States, four BART (Bay Area Rapid Transit) weathering steel superstructures with weathering steel deck systems have been in service since 1972 in the San Francisco, California area. The benefits of steel orthotropic decks — including rapid construction, minimization of dead load and long service life — make them ideally suited for meeting critical infrastructure challenges.

(See presentation on “Portable Orthotropic Bridge System Developed by Province of British Columbia Ministries of Forest and Range” by David Harvey.)

*Photo Credit: Canam Bridges