A Reassuring Sound Above Traffic's Din
Friday, August 3, 2007
With all the advanced technology available in the world, a proper bridge inspection comes down to a pick hammer and a "ping."
Not a "thud." A thud is bad.
A nice, high-pitched ping means the bridge's steel hexagon bolts are tight. And tight bolts mean the intricate lattice of steel diaphragms, cross braces, bearings and splice plates -- in short, the entire superstructure of the bridge -- will hold up as thousands of vehicles pound across it everyday.
A "thud" means the bolts have started to come loose. If all they need is a little tightening, most bridge inspectors carry a yard-long wrench for the job. Oh, there is the occasional need for ground-penetrating radar to check for potholes on the concrete deck above and red dye penetrant or magnetic powder to look for cracks in the steel below. But by and large, bridge inspection is not rocket science.
Ronaldo T. "Nick" Nicholson, a former Virginia Department of Transportation bridge inspector who is manager of the Woodrow Wilson Bridge project, pointed to his eyes. "In bridge inspection, your best tools are these," he said. And, of course, the ears. "It's all visual or audio."
Nicholson explained the intricacies of pings and thuds yesterday under Bridge B609, one of 50 ramps and bridges in the Springfield Mixing Bowl. High above, strapped into an orange lift on the back of a VDOT pickup, Ray Tudge, a bridge inspector of 17 years, wielded his little hammer. From the ground, 35 feet below, Tudge's hammering sounded like a dull "thwack," with an occasional hollow "blang." But Tudge later affirmed that from up high, the noises were indeed pings, just what one would expect from a brand-new, state-of-the-art bridge built to last 100 years.
Nicholson was leading a gaggle of TV cameras and reporters to observe the inspection to reassure motorists that Virginia's bridges were indeed safe after the catastrophic failure of a bridge in Minneapolis. The Maryland Department of Transportation called a news conference to provide the same reassurance. Nicholson said Virginia, Maryland and other surrounding states follow the federal government's rigorous National Bridge Inspection program standards.
Inspectors are trained to make small fixes, such as minor bolt tightening, Tudge explained. To be certified, inspectors must complete a two-week federal program. If he finds a small crack, he drills a hole at one end to keep it from spreading. But if he sees anything that merits watching, he notes it in a report. Cracks are measured. Digital photographs are taken. If he finds something more serious -- say, rust building up in such a way that bolts and rivets are in danger of popping -- he calls in a bridge repair team.
But if he finds a crack, signs of wear or fracturing so serious as to warrant emergency action, he and every other bridge inspector in Virginia has the authority to immediately shut down the bridge. That, Nicholson said, has happened only two or three times in the past decade in Northern Virginia that he can recall.
In Virginia, inspectors such as Tudge are responsible for inspecting 20,000 bridges, about 2,200 of which are in Northern Virginia. They inspect each bridge every two years, more often if the bridges are older or show signs of stress. Parts of the old Wilson Bridge that was demolished last year were of such concern for potential catastrophic failure that bridge inspectors increased some inspections to every six months.
For the most part, inspecting a bridge is tedious, painstaking and not for the faint of heart. For Tudge to eyeball every bolt on this quarter-mile-long bridge in Springfield will take about three weeks, he said -- a month and a half if it were in bad shape. And when he gets to the section that arcs over the pounding interstate traffic, he'll have to use the state's only "bridge snooper," a machine that will lower him over the side of the top deck so he can clamber around the bridge's underside.
Nicholson said he watched with horror as the Interstate 35W bridge in Minneapolis collapsed. The bridge had been inspected in 2005 and 2006. One consolation, he said, is that VDOT has replaced all the similarly styled deck truss bridges in his Northern Virginia district, most recently turning one on Route 7 over Goose Creek in Loudoun County into a pedestrian-only historic byway.
But he does have pressing worries, such as the Washington Street Bridge over Columbia Pike in Arlington County that was built in the 1940s and was not designed to handle the volume of traffic it gets everyday. "That one needs to be replaced," he said, "before something happens."