Development History

Exodermic® Bridge Decks in Service Since 1984

In the early 1980s, Neal Bettigole, a consulting bridge engineer and head of a mid-sized firm headquartered in New Jersey, developed the basic Exodermic® concept. He and his firm had specified filled grid bridge decks for several movable bridges, and he realized that more efficient use could be made of the concrete and steel in a filled grid if the concrete were raised to the top of the grid. Adding a mat of rebar to the slab to handle negative moments promised to improve serviceability by significantly reducing the liveload stress range (and the possibility of fatigue damage) at the weld and punchouts in a grid. (See How it Works for more information on the basic Exodermic® concept.)

As the original Exodermic® deck designs were based on existing filled grid designs, horizontal shear connection between the reinforced concrete slab and the grid was affected by welding "tertiary bars" to the base grid. One inch of these tertiary bars extended up into the slab, and short vertical studs (generally #4 rebar) were welded to them.

The first use of the Exodermic® deck was on the Garden State Parkway's Driscoll Bridge over the Raritan River in 1984.

Early tests of Exodermic® decks were conducted at Lehigh University, and the first use of the design on a bridge was on the Garden State Parkway’s Driscoll Bridge over the Raritan river as part of a reconfiguration and widening of the twin structures. Patents were applied for, and a company, "Exodermic® Bridge Deck Institute, Inc.", was formed. The word "Institute" was dropped in 1997, and the company became Exodermic® Bridge Deck, Inc.

In the early to mid 1990s, it was realized that by starting with a clean sheet of paper rather than adapting existing grid deck designs, a more efficient, more economical, and easier to install deck system would be possible. Thus, the "revised" Exodermic® deck design was developed and then tested.

This revised design has been used on all new Exodermic® deck projects since 1998, and supercedes the "original" design. The revised design has significantly better performance characteristics, is easier to erect, and is significantly less expensive. With the revised Exodermic® design, the tops of the main bearing bars of the grid are embedded directly in the slab, and 3/4" holes on 2" centers at the tops of the main bars act as shear connectors. Horizontal shear flow is direct from the concrete slab to the main bars of the grid.