At the most recent Bridge Grid Flooring Manufacturers Association meeting it was announced that the Carolina Stalite Company has joined the association as an associate member. With nearly 60 years in the business, Carolina Stalite has been committed to manufacturing the finest quality, high strength, low absorption lightweight aggregate in the world. Carolina Stalite is one of the industry leaders in research and production of lightweight aggregates, and will be a knowledgeable associate for bridge owners and designers interested in using lightweight concrete in conjunction with a steel grid deck system. Reid Castrodale, PhD, P.E. from the Carolina Stalite Company stated, “We are excited to work with the Bridge Grid Flooring Manufactures Association to provide the lightest concrete filled bridge deck systems available!”

Located in Pittsburgh, PA, the South 10th Street (Phillip Murray) Bridge was built in 1932 with a grid reinforced concrete deck that is still in service today! The deck is comprised of parallel 3” tees, flush filled with concrete and an asphalt overlay. Now over 75 years old, this is one of the earliest grid reinforced concrete deck installations and has endured much heavier truck traffic and deicing chemicals than originally planned for.

In September 2009, the Pittsburgh office of AECOM conducted an inspection of the deck, and they were very pleased with their findings. Visual inspections of the deck from below showed only minor and isolated corrosion along the bottom of the grid. Given the age of the deck and the potential cost of replacing a deck of this magnitude, AECOM felt it was necessary to take a closer look. The more detailed inspection included hydro-demolition of the concrete fill and asphalt overlay in isolated areas to inspect the internal components and overall integrity of the original steel grid and establish the need for potential replacement. The inspection revealed that the grid is in great condition with only minor, isolated pitting of the steel members while the asphalt overlay has been replaced multiple times throughout the life of the structure. Matt Pierce of AECOM stated “The findings of this inspection and the decision to keep this 78-year old grid deck in service for the foreseeable future, clearly demonstrate how concrete filled grid deck in such applications as the 10th Street Bridge can offer significant life-cycle cost savings to owners.”

The NW 12th Avenue Bridge in Miami-Dade, FL was acknowledged by the Florida Transportation Builders Association with the Major Bridge Award at the 2009 FTBA Convention. One of the commendations of the award was how the contractor, Kiewit Southern Company, tackled the obstacle of a short 72-hour closure window on the busy Miami River. Kiewit’s unique solution involved preassembly of the toe sections for adjoining leaves downriver from the jobsite, then barging and hoisting them into position - a technique that was new to both Kiewit and the FDOT. The new four-leaf, six lane bascule structure replaced the nearly 80-year old functionally obsolete existing bridge.

A major component of Kiewit’s success was the specification of an Exodermic™ deck by Engineer of Record, E.C. Driver & Associates, Inc. Using 4-½ inches of sand-lightweight concrete (115 psf) with a compressive strength of 5,500 psi, the deck weighed approximately 63 pounds per square foot and spanned floorbeams spaced at 13’-2”. The deck is fully composite with the main girders and floorbeams for additional structural efficiency and weight savings. Reduced weight in the deck translates into savings throughout the structure, including the counterweight, trunnion assemblies, drive machinery, structural steel, and piers. Additional benefits of the closed deck system include a solid concrete riding surface that reduces noise, better skid resistance, and reduced future maintenance costs.

The bridge between Michigan’s upper and lower peninsulas opened for traffic on November 1, 1957 with a unique deck configuration - flush-filled 4-1/4” grid reinforced lightweight concrete with asphalt overlay on the outer lanes and open grid deck in the center lanes. At 8,614 feet, the Mackinac Bridge is the longest suspension bridge with two towers between anchorages in the Western Hemisphere.

The 1940 collapse of the first Tacoma Narrows Bridge, due to its instability in high winds, directly influenced D. B. Steinman’s design of the Mighty Mac. Deep stiffening trusses supporting the deck reduce wind resistance and the open grid deck in the center lanes effectively reduce lift creating stability in winds up to 150 miles per hour.

Current Average Annual Daily Traffic (AADT) figures are consistently around 11,000 vehicles per day with roughly 800 trucks per day making the crossing. The Straits of Mackinac receive approximately 110 inches of snowfall during its annual long, cold and windy winter. Unlike most other bridges in the state, the Mackinac Bridge Authority does not use deicing salts to control ice accumulation on the closed deck surfaces of the structure because of its corrosive propensity to vital steel members. Salts are however carried onto the bridge by vehicles entering from the shore roads. The asphalt surfaces have been designed for waterproofing and rut resistance and have been removed and replaced only twice in the 50+ year life of the bridge. The success of protecting grid reinforced concrete decks has been documented and was the topic of a May 2000 BGFMA Technical Bulletin. Although the open grid in the center lanes has undergone some repairs over the years, the original deck of the outside two lanes remains in service and in satisfactory condition.

L.B. Foster Company (NASDAQ: FSTR) is a $500 million company engaged in the manufacture, fabrication and distribution of products to serve the nation’s surface transportation infrastructure. The company is a key supplier to the rail market providing rail, trackwork and accessories to railroads, mass transit, mines and industry. For the construction industry, L.B. Foster sells and rents sheet, H-bearing, pipe piling and micro piles for foundation and earth retention systems. Additional products include precast concrete products, coated pipe and threaded pipe.