THURSDAY, FEBRUARY 14, 2008
Northern Westchester Bureau Chief
Do We Need Another Bridge Collapse?
On January 17, the New York State Department of Transportation (NYS DOT) announced that it would “move to immediately implement the recommendations of the National Transportation Safety Board (NTSB) and Federal Highway Administration (FHWA) based on their investigation of last summer’s Minneapolis bridge collapse.
The NTSB and the FHWA recommendations specifically referred to steel truss bridges. Truss bridges are one of the oldest types of modern bridges, most of which were built before 1940. These bridges were often used for railways where the economics of the simple pin-jointed construction outweighed appearance. Several of these bridges are still in heavy daily use in upper Westchester County.
The Northbound Amvets Memorial Bridge, over the Croton Reservoir, on the Taconic Parkway is a deck truss bridge that was built in 1931. At the time of its construction the 750-foot, triple-hinged, steel truss arch bridge was the longest of its type in the world. While much recent attention has been paid to the aging condition of the Tappan Zee Bridge (completed in 1955), the Amvets Memorial Bridge is 24 years older and is in obvious visible need of immediate repair. Adding to the concern is the considerable daily use this bridge receives. The Westchester
County Planning Department estimates that as many as 75,000 vehicles cross this bridge daily, a total of over 27 million annually.
The New York State County Highway Superintendents Association (NYSCHSA) met in Albany on January 22 to discuss the projected $175 billion in transportation investment needed statewide over the next 20 years. At that conference, Commissioner Astrid Glynn of the NYS DOT remarked, “Maintaining a safe transportation infrastructure is an essential part of encouraging economic growth across New York State. We must advance a strategy including preserving, and updating, our existing assets”.
Commissioner Glynn, in a press release dated January 31, detailed the sources of pressure resulting in the NYSDOT’s increased funding needs; “rising inflation, an aging infrastructure, and an historic lack of sufficient preventive maintenance”. She remarked, “Going forward, projects that increase safety, promote regional economic growth, and demonstrate energy efficiency, will be top priorities”.
Chief among those priorities in our area is the Northbound Amvets Memorial Bridge. The NYSDOT announced January 24 that it had scheduled maintenance for this bridge. But several calls from The Guardian to the NYSDOT regional and state offices as to
what type of maintenance is scheduled for this bridge, went unanswered.
Given the volume of daily traffic, and the age and construction design of this bridge, The Guardian’s concerns, and the concerns of local citizens, need to be addressed by the officials responsible at the state DOT. What do they have to hide?
Local residents have reason to be concerned over our aging infrastructure after witnessing the failure of other, similar bridges around the nation. According to the American Society of Engineers, between 1989 and 2000, there were more than 500 bridge failures in the United States; the average age of those bridges having been 52.2 years.
Bridge overload and lateral impact from trucks, trains, barges/ships, accounted for 20% of the failures. According to a 2003 report by that same society, “Other frequent principal causes are design, detailing, construction, material, and maintenance.” Similar studies conducted between 1977–2000 revealed almost similar trends, with “most failures occurring during the bridge’s service life”.
Even an inspection does not assure that a bridge will not fail as the nation discovered last summer when a bridge in Minneapolis, MN, on Interstate 35, collapsed despite the fact that the bridge had recently passed inspection. The investigation into this disaster, which left
13 people dead, reviewed what testing methods were actually used to determine the existence of any structural weaknesses. This bridge collapse led engineers to reexamine how best to pinpoint and predict metal fatigue.
According to Richard Meyers, a professor of engineering at Virginia Tech, “The number and magnitude of the loads have an influence on fatigue life. If your actual weights have increased over time to a point that’s greater than anticipated, or if you have overloads crossing the bridge on a daily basis without your knowledge, you will get fatigue damage.”
As reported late last year in Design News, an engineering periodical: Whether fatigue is caused by overloading or corrosion, the end result is
micro-cracking of the support steel. Engineers say such cracks, almost invisible to the human eye, can propagate under normal loads that occur later. Even then, however, there’s no guarantee bridge inspectors will be able to see the cracks.
William O’Donnell, Chairman of the American Society of Mechanical Engineers, said, “Typically, today’s inspection technology isn’t going to find microcracks. And even though the crack growth rate may be very small per loading cycle, if you put a million cycles on it, that crack can grow to be quite large.”
O’Donnell suggested consulting engineers can gather crack growth rate data by outfitting bridges with dynamic instrumentation that will provide data on dynamic loads on the bridge. That, however, can’t be done by bridge inspectors, who must climb over miles of structural steel each year in their search for telltale problems.
“Usually, the bridge inspector is stuck with the limitation of just looking to see if the cracks are already there. The technology it takes to do crack growth rate calculations is beyond the bridge inspector’s task,” said O’Donnell. Without a response from NYSDOT officials, The Guardian cannot inform our readers as to what type of inspections are being performed on the Amvets Memorial Bridge, when those
inspections were last done, if the equipment is in place to test for weight loads, and what repairs are needed to correct the corrosion already very evident on the superstructure.
Given the significant number of bridge failures nationwide involving bridges that are over 50 years old, it is reasonable to assume that the Northbound Amvet Memorial Bridge, built in 1931, may be nearing, or beyond, the end of its anticipated useful life. County
residents and all those who drive across and trust that bridge daily are entitled to know what, if any, plans exist to replace it, and what the state is doing in the interim to assure public safety.
Our readers may be assured that The Guardian will continue to seek answers from both the State Department of Transportation and other governmental agencies that need to be forthcoming with regard to the Northbound Amvets Memorial Bridge on the Taconic State Parkway.
Northern Westchester Round-Up
Buchanan: The Nuclear Regulatory Commission fined Indian Point $650,000 for missing multiple deadlines to get its emergency notification system fully operational. This is in addition to a $130,000 fine in 2007 for failing to have functioning sirens. The NRC has set a deadline
for this summer for this system to be fully operational.
Chappaqua: Hillary Clinton, the first viable female candidate for President, easily won the New York State Primary over Barack Obama,
a junior Senator from Illinois. Senator Clinton was accompanied by her family to the polling station at Grafflin Elementary School in her home town.
Ossining: Metro North announced that it will be removing asbestos and lead from its train stations in Ossining, Scarborough, and Philipse
Manor in preparation for renovations at those stations. The renovations will include new staircases, elevators, and overpasses.
Tarrytown: EF Education First, an international language school, applied for a permit to buy the Marymount College campus. This application is expected to be approved at the Village Board meeting on February 19. EF Education First is known to local area high school
students as the parent company for EF Tours, which offers international educational tours.
– Catherine Wilson