General

Metal grid decks, both open and filled with reinforced concrete, have been used in bridge construction since the 1930’s. These deck systems can be considered for both new construction and bridge rehabilitation projects, where weight reduction and/or speed of construction are important considerations. Metal grid decks, filled or unfilled, are typically lighter in weight than a conventional reinforced concrete deck slab with similar flexural capacity. Weight savings can be especially important in movable bridges as well has rehabilitated structures in which a lighter weight deck may reduce the need to strengthen a structure for increased live load capacity. In many cases, filled grid decks have proven to be quite durable. Filled grid decks on bridges such as the South 10th Street Bridge in Pittsburgh, the Walt Whitman Bridge in Philadelphia, and the Mackinac Bridge in Michigan have all provided a service life of 50 years or more.

Metal grid decks typically consist of several panels that are connected together as the system is installed on the bridge. As such, filled grid decks are modular, and may be able to be installed quicker than typical cast in place reinforced concrete deck slabs. In cast-in-place filled grid decks, the grid panels serve as the formwork, leaving little forming to be done in the field. The concrete in the grid deck can also be precast into the grid panels, and the deck set into place as a precast unit, only requiring closure pours between the panels.

The initial installation and construction of a filled metal grid deck is typically more expensive than conventional reinforced concrete deck slabs. However, a filled metal grid deck can prove to be a viable option when life cycle costs are considered, as a filled metal grid deck may not need to be replaced at the same intervals as those required by a conventional reinforced concrete deck slab, or when dead load reduction or speed of construction are important drivers.

The Bridge Grid Flooring Manufacturers Association (BGFMA) is an industry group comprised of companies who fabricate and supply metal grid deck systems for bridges (11). The BGFMA focuses on the use and design of steel grid decks through data collection, research, development, and education. Several technical documents concerning metal grid deck systems are available at the BGFMA’s website (www.bgfma.org).