Firm touts engineering design concept for state’s bridges

An engineering firm has come up with a more efficient bridge replacement concept that company officials claim could benefit the state at a time it is ready to begin upgrading its deteriorating network of transportation infrastructure.

Rettew, a Lancaster-based engineering firm with offices in Williamsport, has pioneered the geosynthetic reinforced soil-integrated bridge system, or GRS-IBS.

Constructed with readily made materials, the structure consists of concrete retaining wall blocks layered with a synthetic fabric known as Geogrid.

Durable abutments result by filling in the layers with compacted stone materials, and a prefabricated bridge is placed on the abutments.

The result is a less costly and more quickly constructed bridge than conventional span replacement projects.

Dave Hoglund, group manager of Transportation, noted that GRS-IBS bridges are between 50 to 60 percent cheaper than bridges of traditional reinforced concrete.

While conventional bridges can take months to finish, GRS-IBS spans normally take just a few months to complete, he said.

In addition, when designed and constructed according to required specifications, GRS-IBS bridges are as structurally sound as conventional bridges.

“In some respects one could argue they may be more structurally sound,” Hoglund stated in an email to the Sun-Gazette. “Conventional abutments of today rely on rigid, reinforced concrete masses to resist the combinations of forces from the bridge it supports and the soil backfill behind it. When those outside forces are not consistent, the concrete might crack and expose the steel reinforcement to the weather, which might in turn further deteriorate the structure if not addressed.”

Also, the geosynthetic reinforced soil system is more flexible resulting in more uniform distribution of varying stresses.

Geosynthetic reinforced abutments have been constructed throughout the U.S., including Pennsylvania, Ohio, New York, Washington, California and Colorado.

The technology has been used to construct retaining walls, slope stabilizations and other similar structure applications for about 30 years.

Hoglund noted the design process is applicable to single-span bridges where the abutments and wing wall height does not exceed 30 feet.

Span lengths of up to 140 feet have been constructed, although they are typically less than 100 feet.