Launch Slideshow

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Bridging the Gap

Bridging the Gap

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    Workers core-drilled and installed 38 reinforcement anchors to increase the capacity of the 180-year-old Aldie Bridge in Virginia.

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    Of the 1778 masonry bridges in the U.S., more than half are either functionally obsolete or deficient.

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    Many of the 1778 masonry bridges in the U.S are concentrated in the Northeast and Mid-Atlantic.

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    The ends of the arch of the 152-year-old Cattle Pass were unraveling because the exposed brickwork at the ends collapsed.

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    Workers rebuilt all of the loose or missing brickwork in the intrados using existing brick to limit differential moisture growth where possible.

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    The completed arch restoration.

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    Kirkwood Masonry in Missouri has developed its own niche by building small masonry bridges on golf courses, including this one at Greenbriar Hills Country Club in Kirkwood, Mo.

In the last six months, the airwaves have been filled with how the federal government's stimulus package will be pouring work back into the marketplace. The first wave of this effort is beginning to spur construction, primarily on our nation's highways.

So how can mason contractors capture a part of the package? One potential opportunity could be bridges.

At first glance, masonry bridges don't seem to be a large market. There are only 1778 masonry bridges in the U.S., according to the Federal Highway Administration's 2008 National Bridge Inventory (NBI). It's a surprisingly small number, representing less than 1% of all bridges in the nation. And the market, at least on highways and streets, isn't likely to increase. No new masonry bridges were commissioned in 2006, the latest year of data, according to the NBI.

So where is the opportunity?

At least on the infrastructure side of the equation, mason contractors should look at the opportunity in repair. In 2008, 54% of the existing masonry bridges were either functionally obsolete or deficient. By material type, masonry has the highest percentage of bridges requiring immediate attention. The next highest category is wood (49%). This means that masonry bridges either do not have the load capacity to handle current traffic ratings, or they're too small to handle traffic volume.

Saving our legacy bridges

One method in the U.S. is the Archtec system. Since 1999, this has been used to asses the strength of more than 300 bridges and physically strengthen more than 200 bridges across the world. Workers install stainless steel reinforcing bars and grout them into the masonry. Materials are selected to ensure durability.

To protect the surrounding masonry from displacement or damage during grouting, the reinforcement t bars and grout are contained within a “sock.” As the grout is injected during inflation, the sock deforms s and permits sufficient leakage to allow chemical and mechanical bond ding to the masonry.

The efficacy of this connection is evaluated by pull-out tests. The reinforcement is positioned in the arch barrel in a longitudinal direction and tangential to the curvature. Numbers and precise disposition of the bars are confirmed by advanced numerical analysis using ELFEN, a non-linear discrete element program. This enables the composite behavior of the reinforced masonry to be predicted and allows accurate simulation of its response to permanent and live loads.

In North America, the system has been widely used to repair several high-profile masonry bridges. One was a 180-year-old stone arch bridge which carries U.S. Route 50 over the Little River in Aldie, Va. Upon inspection, engineers found that one wing and spandrel wall bowed out dangerously, and a support buttress was showing signs of accelerated weathering due to mortar joint deterioration.