Infrasense Scans Sagging Leo Frigo Bridge in Green Bay, Wisconsin, Using Ground Penetrating Radar

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The Leo Frigo Bridge has been closed to traffic since late September following the corrosion and subsequent settling of the pilings below one of the piers. Infrasense responded on short notice to WisDOT's need for a condition evaluation of the sagging portion of the bridge deck using ground penetrating radar (GPR).

Infrasense engineer inspecting the surface of the sagging portion of the Leo Frigo bridge

The Leo Frigo Bridge is an 8,000-foot long bridge over the Fox River in Green Bay, Wisconsin, that typically carries around 40,000 motorists each day. The Leo Frigo bridge has been carrying traffic into and out of Green Bay since it opened in 1981. The bridge carries Interstate 43, a major route into the city and to many Green Bay attractions, including nearby Lambeau Field.

In late September, pier 22 sank approximately two feet due to corrosion of its pilings and caused a significant sag in the structure. The Leo Frigo bridge has remained closed to traffic since September 25. Current construction plans, which include installing new pilings to piers 21 through 25 and jacking the deck back into place at pier 22, will allow the bridge to reopen in January 2014. However, engineers at the Wisconsin Department of Transportation (WisDOT) had concerns about the condition of the bridge deck, especially under the changing loads and stresses associated with the sagging span and temporary bracing.

In order to assess the condition of the bridge deck, WisDOT called in Infrasense, Inc., a national leader in detecting subsurface conditions. Infrasense performed vehicle-based Ground Penetrating Radar (GPR) testing across the entire width of the Leo Frigo bridge from pier 21 to 23 in order to investigate the subsurface condition of the sagging portion of the bridge deck. Infrasense responded on short notice to carry out the work in early November, and was among the first vehicles to drive onto the sagging portion of the bridge after the temporary bracing was installed.

GPR is just one of the methods being used to evaluate the structure and ensure it is safe to reopen to the public. In this regard, Infrasense was able to meet a tight project schedule and provide the deck condition results to WisDOT within a week of the data collection.

Ground penetrating radar (GPR) data is collected to estimate rebar depth and corrosion conditions. The GPR data is collected in a series of lines spaced 3 feet transversely across the width of the deck, with each line representing a cross sectional slice of the deck at a particular offset. Decks in good condition consist of strong and uniform radar reflections from the rebar. GPR data with weak and inconsistent reflections indicate rebar-level deterioration in the bridge deck. GPR condition information is used by agencies at a management level, to distinguish, categorically, that level of action required to preserve a group of decks. That is, for example, which decks require minor repairs, patching, an overlay, or replacement. Additionally, once these higher-level decisions are made, GPR can be used as a scoping tool to determine the extent of repair required for a particular deck.

About Infrasense, Inc.

Since 1987, Infrasense, Inc. has applied the most current technologies to the most difficult challenges in subsurface scanning. Infrasense’s engineers are able to nondestructively extract critical information from a diverse range of structures. The firm has conducted research to advance the field of subsurface detection, while also providing valuable information to clients across the country. Learn more about Infrasense, Inc. and its services at

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Sarah Kelly
Infrasense, Inc.
+1 (781) 648-0440
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Infrasense, Inc.

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