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"  The Verrazano-Narrows Bridge, one of the longest suspension bridges in the world, spans the length of the strait dividing the New York City boroughs of Staten Island and Brooklyn. But nearly 100 miles away, in a warehouse in Bethlehem, Pa., a much needed upgrade for this heavily used bridge is proving its worth.  The Verrazano, put simply, is overtaxed. An estimated 190,000 vehicles cross the bridge every day, keeping the Triborough Bridge and Tunnel Authority (TBTA) constantly at work. &amp;quot;We take care of potholes and the general substructure of the bridge,&amp;quot; says Sam Tabikh, project manager on the TBTA&amp;#039;s Verrazano-Narrows Bridge replacement deck project. &amp;quot;The integral part of the deck is steel repair, which runs in the hundreds of thousands [of dollars].&amp;quot;  The wear and tear\u2014and thus the need for repair\u2014got worse after Sept. 11, 2001. Fearing further terrorist attacks, the TBTA began to restrict all truck traffic to the Verrazano&amp;#039;s upper deck. The thinking was that if terrorists attacked the bridge with a bomb aboard a truck, the blast would do greater damage if it happened on the more contained lower deck, while any blasts on the upper deck would dissipate more into the open air. The decision may have made the Verrazano safer, but the amplified weight on the upper deck accelerated fatigue in the steel and concrete. &amp;quot;The damage done to most bridge structures is from traffic and heavy loads,&amp;quot; says Sougata Roy, a senior research scientist at Lehigh University&amp;#039;s Advanced Technology for Large Structural Systems (ATLSS) Center. &amp;quot;What happens in traffic is repeated loading, and if you keep repeated loading, fatigue damage will increase.&amp;quot;  The bridge needs a major fix for the long term, and that&amp;#039;s where Roy and his colleagues come in. In their vast warehouse-like testing facilities at Lehigh, researchers are running stress tests on a prototype of a replacement-deck segment designed by Parsons Transportation Group of New York. The prototype has six hydraulic actuators bolted in a fixed position above the deck, and three actuators bolted below it. The actuators are basically giant hydraulic pistons that can apply differing degrees of pressure to the steel deck. To mimic the weight and movement of a vehicle, the actuators apply pressure to the deck in sequence, one after the other, just as a moving car or truck would. The more pressure the hydraulic actuators put against the steel deck, the heavier their imaginary vehicle is.      The ATLSS team&amp;#039;s task is to accelerate fatigue. They try to condense decades upon decades of vehicular bridge use into a matter of months. To do it researchers and students at ATLSS work around the clock. But aside from the conversational buzzing, the laboratory is surprisingly quiet. Although you&amp;#039;d expect the hydraulic actuators to be loudly whirring and buzzing, the massive pistons produce a very minimal amount of noise. In fact, Roy says, if you were to stand underneath the prototype structure with the actuators turned on, it would sound similar to actual trucks passing over the bridge, right down to the slight rumbling when the vehicles pass overhead, says Roy. Every 4 hours, Roy and his team visually inspect the structure for cracks. If they find any, Roy reports them back to the bridge&amp;#039;s designers, who will correct the final design of the replacement deck. The old bridge deck still in use is made of a steel grid filled in with concrete. Despite its strength, concrete is sure to have tiny microscopic cracks upon hardening. As the deck withstands rain and snow, water slips into the cracks and accelerates corrosion. Concrete decks are given a shelf life of 45 to 50 years or so before regular maintenance is needed just to keep the deck in shape. The Verrazano has been in active use since 1964, so it&amp;#039;s time for a revamp.  With the new deck, it&amp;#039;s out with the cracking concrete. The new design is a steel orthotropic deck that beats concrete in several key ways, Roy says. Orthotropic decks incorporate two different stiffnesses of steel that run in two different directions. In one direction, the direction of traffic, the steel is tough and rigid. However, the steel that runs perpendicular to the flow of traffic is relatively flexible. Orthotropic decks are also 100-percent steel\u2014no concrete. The design requires less material overall, and steel generally corrodes more slowly than concrete. Once the testing at ATLSS is concluded, the Verrazano&amp;#039;s new deck will be fit into place in New York much like the pieces of a puzzle: segment by segment, lane by lane. According to Tabikh, work on the bridge is projected to begin in 2012 and end roughly around 2017. With the new deck in place, the bridge will look about the same from afar. But in terms of longevity, the Verrazano will have been given a new lease of life. One of the ATLSS&amp;#039;s goals is to ensure that the replacement deck will last a century, on par with recent suggestions from the Federal Highway Administration. &amp;quot;They want the deck to last a hundred years or more,&amp;quot; Roy says, &amp;quot;And our job is to ensure that it can be done.&amp;quot; "^^<http://www.w3.org/2001/XMLSchema#string>
<http://www.popularmechanics.com/technology/infrastructure/a6556/how-to-fix-a-suspension-bridge-the-verrazano-narrows-upgrade-5518985/>