| BUILDING BRIDGES FOR THE 21ST CENTURY AND BEYOND More than a half million bridges carry cars and trucks across rivers in the United States every day. Of those bridges, the U.S. Department of Transportation estimates one in four is considered structurally deficient or functionally obsolete. Really, not surprising given that the majority of U.S. bridges are 50 to 60 years old having been built in the 1950’s and 60’s after the signing of President Eisenhower’s Federal Highway Act. It may be coincidence, but two of the largest bridge failures in the past decade occurred on bridges built during that time period. Minnesota’s I-35W Bridge, which opened to traffic in 1967 after three years of construction, came down during the evening rush hour in 2007 sending dozens of vehicles into the Mississippi River. Even though the bridge on Interstate 35 was the second busiest span in all of Minnesota, and even though the bridge had been flagged as “structurally deficient” beginning as early as 1990, construction of a new bridge was not scheduled to take place until 2020. Nearly six years later, a portion of another bridge on another major artery, I-5 in Washington State, collapsed after an oversized truck carrying a load to Vancouver struck several overhead support beams. This span, crossing the Skagit River and built in 1955, had already been flagged as "functionally obsolete” because it didn’t have redundant load bearing beams. Put another way, engineers recognized the failure of just one critical part could cause the whole bridge to come down. In spite of the above examples, the Federal Highway Administration insists U.S. bridges are safe. It says the structurally deficient or functionally obsolete designations simply mean a bridge either has a structural defect requiring the addition of a load or traffic limit, or in the case of a “functionally obsolete” bridge like the Skagit River Bridge, is carrying more and heavier traffic than originally intended. Whether federal and state experts consider the bridges unsafe or not, there is agreement that the bridges are, at the very least, vulnerable. The good news is states are working to fix or replace many of these more vulnerable bridges. A $4 billion replacement of New York’s Tappan Zee Bridge is the largest bridge project underway in the U.S. now, but it’s certainly not the only one. Projects are underway in all fifty states with the most urgent work taking place in northern states by crews trying to beat the arrival of winter. Before construction crews can do anything though, they need steel. In any given year, Casco Bay Steel Structures will see more than 20,000 tons of steel pass through its doors. From two locations in Maine, more than 100 people work to cut and weld steel girders together. These girders aren’t exactly small. Oversized trucks, forklifts, and heavy cranes lumber across a 30 acre yard. Delivering steel, unloading steel, moving steel; starting in the early morning hours and going late into the night. This steel will make its way into one of Casco Bay Steel’s two long fabrication facilities and eventually to projects throughout New England, New Jersey, and New York.  Like the rivers they cross, every bridge and the girders that support them, are different. Some are straight, some are curved, some are tapered, all with variable depths and lengths. The longest span to leave Casco Bay: 172 feet, more than half the length of a soccer field. The heaviest? 89 tons. As no company wants to fabricate a defective girder that could find its way onto a bridge used by thousands of cars and trucks a day, Casco Bay Steel’s fabrication process is highly disciplined. From the sourcing of the raw steel, to the final smoothing of the beam, the work is carefully done with several inspection points along the way. Though Casco Bay Steel is less than 20 years old, its president, Bryon Tait, is well versed when it comes to the fabrication of structural steel. He started in the business when he was 19, more than three decades ago. In that time, Tait has seen a lot of changes in the way girders are constructed. Today the process is faster and more automated. “The technology today has actually helped us produce more product with fewer hours and keeps us competitive. There are fewer of us today than 30 years ago, yet we’re producing more,” Tait says. One of the most notable changes for him was the move from oxyfuel to plasma cutting. Casco Bay Steel added plasma about seven years ago. Tait says improvements in cut speed alone made a huge difference. Casco Bay Steel went from cutting five inches of steel per minute with oxyfuel to 115 inches of steel per minute with Hypertherm plasma. As an added bonus, Casco Bay Steel found the cut quality when using plasma was better as well. “The quality of cutting that we have to use for our process is actually minus zero plus a sixteenth,” Tait explains. “We have to have nice square cuts with no gouges and Hypertherm gives us that.” In total, Casco Bay Steel uses two Hypertherm systems, a HyPerformance HPR260XD and HPR400XD. The thickness of steel cut with the systems can vary, though the most commonly cut thicknesses are in the 1/2 to 1 inch range. “We were impressed with the cut quality from Hypertherm. Once we saw the difference Hypertherm made, we wanted to make sure all of our future systems were Hypertherm.”  Two Hypertherm HyPerformance systems grace Casco Bay Steel facilities including this long table system. Among the girders fabricated with plasma are a series of steel girders used on a bridge in Hypertherm’s own backyard. Not even four miles from a major Hypertherm facility the New Hampshire Department of Transportation is replacing a bridge in service since 1927. The bridge has served admirably, but nonetheless nearly 90 years of traffic has taken a toll. The concrete pillars that hold the structure up over the Mascoma River are crumbling. The girders and rods are rusted and exposed. When the bridge was built nearly 90 years ago, the automotive scene looked quite different. There were an estimated 20 million cars on the road, an average of one car for every two U.S. families. Today, the numbers are reversed. Each U.S. family owns at least two cars. In all, more than 250 million cars and trucks traverse U.S. roads. An estimated 17,000 of those travel U.S. Route 4 over the Mascoma River every day; a number expected to nearly double by 2030. “There’s so much more to building a bridge today than 50 years ago,” says Peter Kehoe, a civil engineer with the New Hampshire DOT. “For example, environmental concerns, especially since the Mascoma River serves as a drinking water source for the City of Lebanon, and also traffic control issues. This route carries 17,000 cars a day and you need to make accommodations for that with detours, flagging, etc.” To improve safety and sight distance, the bridge going up now is quite a bit wider than the original 1927 span. Five variable depth plate girders, ranging from 86 to 125 feet in length and weighing a combined 430 tons, are spliced with a friction type connection to cover the 440 foot long span. The bridge is engineered to last 80 years, but Kehoe believes the solid construction will keep it operational well into the next century.  Old vs. new: the original Mascoma River Bridge next to its replacement with plasma cut girders. It took Casco Bay Steel about six weeks to complete the fabrication process and a construction team three weeks to erect and install the girders at the bridge site. “We are seeing more plasma being used on bridges now. Not just the bridge girders, but also the cranes and end dams to the bridge expansion joints,” Kehoe says. The first cars and trucks began crossing the new Mascoma River Bridge this month but the crew’s work is not done yet. Instead, they are moving next door to begin demolition of the old bridge. After that, it’s on to the next project which, for better or worse, there is no shortage of as the NHDOT works to replace another bridge on its list. |
 |
 |
| Connect with us: |
| Summer 2015 |
| CUSTOMER SPOTLIGHT |
 |
 |
 |
 |
 |
21 Great Hollow Rd, PO Box 5010, Hanover, NH 03755 USA
|
| Girders and plates of steel stretch through Casco Bay's South Portland facility. |