Eight feet. That's how far Manhattan Bridge swings from one extreme to the other when a subway train crosses. The train tracks are on the outside of the bridge, with a lower roadway between them and an upper roadway above them on each side.
"They placed the subway tracks on the outside instead of in the center as they did on the Williamsburg," Tom Nilsson, project manager for Koch Skanska, told Roads & Bridges. "It's fine when you have subway trains on both sides," but when there is a train on just one side, the swing puts tremendous stress on certain parts of the bridge.
"What's being done right now is that we basically are replacing all the bad parts," said Nilsson. "In addition, we are stiffening the bridge to minimize this movement."
Manhattan Bridge is the youngest and the widest of the three historic suspension bridges across the East River. Williamsburg Bridge lies to the north and Brooklyn Bridge to the south.
Construction of Manhattan Bridge began in 1901. It was opened to traffic on Dec. 31, 1909. It has a total length of more than 6,000 ft, with a main suspended span of 1,470 ft. The four suspension cables are each 3,224 ft long and 21.25 in. in diameter. The towers stretch 336 ft high.
To stiffen the bridge and cut down on the swing, Koch Skanska Inc., Carteret, N.J., is adding steel in the form of cross-members, called upper laterals, positioned under the lower roadway.
Koch's contract with New York City is worth about $175 million, but with added work it will probably come to $200 million. The extra items include installing a bicycle lane (the original bridge had no pedestrian or bicycle lanes), renovating the colonnade at the Manhattan entrance to the bridge, replacing the subway tunnel roof where it comes off the bridge and goes underground and installing new maintenance platforms and netting.
Koch's original contract for the north side of the bridge included stiffening the suspended spans; replacing the truss bearings on the approaches; removing all the lead-based paint and repainting; reconstructing the subway framing; reconstructing the upper roadway in the suspended spans; rehabing the approach spans, elevated structures and subway tunnels; and installing an intelligent transportation system.
The work on the south side of the bridge was done previously under different contracts to another construction company.
Some assembly required
The south-side work took six years to complete. Koch began its north-side work in February 2001 and plans to finish in July 2004. Prefabrication is helping Koch shorten the construction time.
"We pre-assemble everything we can possibly pre-assemble into the largest pieces we can handle," Terrance Daly, vice president of Koch Skanska, told Roads & Bridges. "You get everything together someplace, put it all together, make sure it fits perfectly and then take it apart in the biggest pieces possible."
When the pieces get to the jobsite, they simply install them as planned, with no delays for workers to figure out what to do next. The subway framing, for instance, was fabricated off site and delivered in large pieces. The concrete sidewalk pieces were poured in New Jersey and delivered by truck in 18- x 12-ft sections.
Koch also prefabricated new truss bearings, but replacing the old ones took more than a little assembly.
The bearings under the deck between the bridge truss and the support piers on both approach spans are original equipment installed 100 years ago to let the bridge respond to shifting caused by factors like temperature, wind and traffic. Over the years, the bearings have suffered from ordinary wear and inadequate maintenance.
"They're overdesigned, but when you don't grease them and you don't clean out the bird crap and the rust and the paint, they just wear themselves out," said Daly. "Some of them were actually frozen when we got there."
The old bearings were roller bearings, and some of the pins were so worn they had flat spots. The new bearings are pot- and disc-type bearings made of stainless steel and Teflon to reduce friction.
Getting your bearings
To remove the old bearings and install the new ones, Koch Skanska had to engineer a complicated "jacking frame" built of steel sturdy enough to stand in for the bearing in supporting the bridge.
"We bear on top of these piers, and we actually lift the bridge off the existing bearings," said Daly, "and hold it there for a couple of weeks while we pull out the old bearings and put in the new ones."
The jacking frame has to support loads of up to 2,000 kips (1 kip = 1,000 lb). Koch is replacing about 32 bearings at 16 locations.
The rehab has been a major disruption to traffic across the bridge. On an ordinary day with all lanes open, the bridge carries about 78,000 vehicles and about 266,000 subway riders, the most subway riders of any bridge into New York City.
With so much traffic on the bridge, it is understandable that Koch faces penalties if it is late finishing its work. The company has already met its first and second milestones and avoided any disincentives. It is in the midst of meeting the third milestone, reopening the upper roadway.
"We think we can be on time and probably a little bit early," said Daly, "so we're anticipating collecting some of the bonus money."
If Koch finishes early, the company can collect $50,000 per day. If it is late, it can be penalized the same $50,000 per day.
The fourth milestone, completion of the subway and painting, Daly said will be the toughest to meet.
"Right now we feel we're on time," he said, "but we've also taken on about $12 million worth of extra work that has to be completed in this milestone. We're still confident we can make this milestone."
The final milestone is completion of the entire job, and Daly is confident it will happen on time.
Removing the lead-based paint to meet the fourth milestone is the most environmentally sensitive part of the Manhattan Bridge rehab job. Most of the work of removing the old paint and applying modern paint is being done under a $20 million subcontract to Campbell Painting, New York.
The city originally planned to remove the old paint after the other work was completed, but Koch requested that the paint come off first.
"We had the city change that to remove all the lead first," said Nilsson, "and then we go and do our work, which really brought down our lead exposure."
The Manhattan Bridge painting job requires a Class 1A containment structure as specified by the Structural Steel Painting Council.
The containment is a tent-like structure that is hooked up to ventilation equipment that continuously removes contaminated air, filters it and replaces it with clean air. The containment area is about 100 ft long and encloses the entire north side of the bridge structure.
The city specified using recyclable steel shot instead of conventional sandblasting sand. Using steel shot, which looks like tiny BBs, greatly reduces the amount of waste material generated.
"When you use conventional blast medium," Daly explained, "the medium becomes a waste byproduct of the operation. You use the shot to sandblast the steel and then you go back and recycle the shot, and the waste byproduct is greatly reduced.
"At the end of the shift, they vacuum it all up along with the waste they've generated from the lead," he continued. "It goes into a special machine and it gets scrubbed and sorted. The waste byproduct gets kicked out and then they reuse the shot."
The only physical drawback to using steel shot for blasting is that if the BBs get wet through humid air or some other source, the shot can rust together into a mass that clogs the equipment. Daly said the Manhattan Bridge operation had run into no problems.
The city may have reconsidered using steel blasting shot after seeing how expensive it is to work with. The trade-off with the recyclable shot method of paint removal is that it is more expensive to perform but less expensive to dispose of the waste. It is less expensive to do conventional sandblasting but more expensive to dispose of the waste.
After specifying steel shot for the Manhattan Bridge work, Daly said, the city has given Koch the choice of methods on future projects.
In late October, Koch Skanska was about 50% finished with its work overall on the north side of Manhattan Bridge. The upper roadway was about 75% finished and scheduled to open this June. The truss bearing replacement work was about 25% completed. The repainting work was about 90% finished.