BRIDGE REHABILITATION Steel Is the Workhorse

38 Metals in Construction Spring 2008 Rehabilitation 39 Given the well known resiliency of structural steel, the Manhattan Bridge will stand for at least 75 more years before another reconstruction of this scope goes up for consideration.

Previous 80,000 vehicles and 320,000 Above The bridge’s suspender cables transit riders cross the Manhattan Bridge were replaced. every day. Facing The rehab replaced the span’s floor beams and decking.

The Manhattan Bridge has repeatedly been of the Manhattan Bridge was bridge engineer Moisseiff’s design, NYCDOT hired Weidlinger Although slightly different in appearance from the elements, corrosion from pigeon droppings, that sit on masonry piers have been replaced described as the workhorse of the East River Leon Moisseiff, known for his work on deflection Associates as designer and structural engineer the old lateral bracing, the new steel members and an overall neglect that characterized New with Teflon-coated multi-rotational bearings that spans. So it was no surprise that, after nearly a theory and subsequently designer of many other on the rehabilitation project. Assessing the are barely visible to drivers. All of the ’s understandably laissez-faire approach have a very low friction coefficient. Installing the century of service, the crossing was found to be famous spans employing this concept. The situation, the firm worked out a scheme to lateral members are built-up T, reversed U, or to infrastructure during the fiscal crisis of the new bearings was a feat in and of itself. After in dire need of repair. In response, the New York concept asserts that the stiffness of a bridge brace the bridge’s under-designed lateral stiff- H shapes, with the flanges welded to the stem. 1970s. These cavities and weaknesses were installing a temporary steel frame underneath City Department of Transportation (NYCDOT) deck could be decreased with more dead load, ening system with new structural steel members, All connections are made using A325 high plugged over time with steel plates fastened the crossing’s trusses, Koch closed the launched a bold 15-phase rehabilitation effort meaning the longer bridges were the more thus creating a “torque tube,” which along strength bolts. The cost of this phase of the work via high-strength bolts. bridge to subway and car traffic, then hydrauli- that began in 1982 and, with completion flexible they could be. Thus stiffening trusses with re-decking the bridge and re-anchoring its represented approximately 10 percent of the In the case of the bridge’s signature decora- cally lifted the bridge a half-inch, clearing enough expected in 2013, is nearing $1 billion in costs. could be minimized for longer, inherently heavier cables ensured that this vital city artery would total budget. The larger proportion of project’s tive work, which includes canopy structures, room to switch out the deteriorated load bearings. As part of this effort, the bridge’s four stiffening bridges in Moisseiff’s view, and this innovative not deflect more than three feet. steel contract was devoted to deck replacement. handrails, and informational plaques, “we paid One final aspect of the rehabilitation efforts trusses have been reinforced, the decking and thesis formed the underlying principal of the The torque tube plays the vital role in Divided into separate contracts, crews ultimately attention to the original architectural details that involved meticulously removing the bridge’s bearings have been replaced, and the main East River span. But in the early 1900s, minimizing deflection. Weidlinger reinforced replaced approximately 1,600 roadway and are evident and unique to the bridge,” Terrence lead paint and recovering the structure with cables have been re-anchored, work encom- deflection theory wasn’t advanced enough the lower lateral bracing, located beneath the subway track floor beams, and many more Daly, senior vice president of general contracting safer and more durable epoxy coating—in passing thousands of tons of structural steel. to accommodate the complex conditions of bridge’s lower deck, and installed all-new lateral stringers. The existing roadway beams were firm Koch Skanska and steel erector, says of the bridge’s famous blue, of course. Still, Brian Now, owing to the material’s enduring strength the Manhattan Bridge: For reasons that are bracing underneath the upper deck (the original built-up, riveted members, the ones replacing the castings that were undertaken. “Some of Gill, the engineer in charge of the project for and flexibility, the 1,470-foot main span of the now unexplainable, Moisseiff decided to run the had been removed in the 1950s due to visible them are welded plate girders of the same that work is so unique for a contractor that it’s NYCDOT, emphasizes that better defenses do Manhattan Bridge is ready to continue carrying subway train tracks along the outer edges of cracking), forming a four-sided shape that led size, but with improved section properties and difficult to price correctly. It’s not something not preclude more regular maintenance. Each the 80,000 vehicles and 320,000 mass transit the roadway, instead of running them down the to its “tube” designation. The engineers also stronger Grade 50 type steel. The new members we do as a normal course of business.” maintenance schedule depends on the compo- riders that cross it everyday well into the future. middle. As a result, the subway cars exerted in- added 16 end frames to the towers and anchor- are connected to the trusses with bolted con- Whereas the ornamental metal work nent, he says, although, say, spot-patching the Originally intended to relieve the credible torque on the structure. The workhorse, ages in order to better transfer twisting load nection angles using high strength bolts. But demanded a historically respectful approach, paint—one of a bridge’s best barriers against Bridge’s throngs, the Manhattan Bridge was the it turns out, was a bucking bronco—its deck tilt- into vertical load. The new steel reinforcing and not all floor beams beneath the upper roadway stiffening measures permitted an injection of high corrosion—can happen anytime. But given the first East River crossing to accommodate vehi- ing as much as eight feet under the weight of a bracing members are attached to the trusses were replaced, meaning that the bridge still hosts technology. For all members, ASTM A588 Grade well-known resiliency of structural steel, he ex- cles as well as subways traveling in both direc- loaded train, forcing suspension cables to shift via new, larger gusset plates, which vary in size some older patch repairs made to counter sec- 50 steel, which has atmospheric corrosion pects that the Manhattan Bridge will stand for at tions when it was completed in 1909. But not all relative to and abrade against the steel trusses. depending on the forces present at the connec- tion loss. Indeed, whole chunks of the structure resistance properties, replaces older Grade 36 least 75 more years before another reconstruc-

firsts equate to bests. Among the designers To find a solution to the problems posed by tion, but are never less than ¾ inch in thickness. and this page: NYC DOT Bridges Previous NYC DOT Bridges had disappeared as a result of long exposure to material. And in the approach spans, the bearings tion of this scope goes up for consideration. M

40 Metals in Construction Spring 2008 Manhattan Bridge Rehabilitation 41 Facing and above Rehabilitation efforts included restoring the bridge’s signature ornamental ironwork.

MANHATTAN BRIDGE REHABILITATION

Owner: New York City Department of Transportation, New York, NY Designer and Structural Engineer: Weidlinger Associates, New York, NY General Contractor: Koch Skanska, Inc., Carteret, NJ Structural Steel Fabricator: American Bridge Manufacturing, Coraopolis, PA Structural Steel Erectors: Northeast Structural Steel, Mt. Vernon, NY; Koch Skanska, Carteret, NJ Miscellaneous, Architectural, and Ornamental Metal Erectors: Northeast Structural Steel, Mt. Vernon, NY;

NYC DOT Bridges Koch Skanska, Carteret, NJ

42 Metals in Construction Spring 2008 Manhattan Bridge Rehabilitation 43