Span awaits assembly

Sections of Bay Bridge deck are fabricated in Sparrows Point

September 06, 2007|By Michael Dresser | Michael Dresser,Sun Reporter

The Bay Bridge road surface you might be driving on next summer lies in stacks today in a weedy, open-air storage area on the sprawling Sparrows Point steel mill complex.

It is there that a contractor for the Maryland Transportation Authority is fabricating the immense sections of bridge deck that will be put aboard tractor-trailers and barged down to the Bay Bridge, where they will be put together as if pieces in a giant puzzle. The transport operation is expected to begin in the middle of this month.

Yesterday, toll authority officials invited the media in for a glimpse of what is taking place at the heavily secured facility. It was, in effect, a short course for nonengineers on the anatomy of a bridge deck.

The public relations effort comes as doubts are being raised about the quality of American bridge engineering in the wake of the Aug. 1 collapse of the Interstate 35W crossing of the Mississippi River in Minneapolis. Thirteen people were killed.

As Maryland officials prepare to proceed with the second phase of the replacement of the deck of the Bay Bridge's three-lane westbound span, the authority faces questions about its performance in the first phase.

The project ground to a halt three years ago when inspectors found that the new concrete surface on parts of the bridge was cracking. A subsequent investigation found that the concrete did not properly adhere to the undersurface of the bridge when temperatures dipped.

Much of the repaving had to be redone, and motorists were subjected to some of the worst delays in the bridge's history as extra lanes were closed to finish the work.

The fiasco prompted the authority to rethink its approach to the second phase, which is expected to cost about $60 million. It decided to abandon efforts to pour the concrete surface on-site and instead to replace the current deck section by section on the suspension and "through truss" portions of the bridge.

Geoffrey Kolberg, chief engineer for the authority, explained that fabricating the bridge off-site has advantages in quality control and in reducing the need to close lanes.

`A better method'

"This is a better method, much more predictable, better controlled," Kolberg said.

That doesn't mean it's exactly a stroll though the park.

The scale of the challenge can be seen in the storage area, where more than 130 concrete panels - each cast to fit seamlessly with adjacent panels - await their barge voyage to the staging area just south of the bridge on the Western Shore.

Each slab weighs 25 to 50 tons, Kolberg said, and is 34 to 40 feet long and 16 to 18 feet wide, with concrete "muscle" encasing a skeleton of steel girders and rebar.

The surface where the rubber will meet the road is rough to the touch, with hundreds of grooves in the pavement to increase traction. Kolberg said the sections are slightly curled so that the grooves carry water off the bridge, preventing cracking.

Each of the sections is fashioned from scratch by employees of American Bridge and its subcontractors, working out of leased space at the now largely empty steel complex.

Some of the work is painstakingly done by hand. Yesterday, several workers were bent over, twisting the wires that would hold together a section of the gridlike steel rebar that reinforces each section. Nearby, other workers created a racket as they pounded the steel frames into place.

In the nearby casting shed, a structure renovated for the bridge project, the epoxy-coated steel frame and rebar, as well as white conduit tubes that will hold steel tension rods, are assembled in a forming tray. Then the concrete is poured to encase the steel structure and steam-cured.

Kolberg said the operation has been able to make four deck sections a week and has almost completed fabrication of the 144 pieces of the deck of the suspension section of the bridge, the highest part of the span. When that work is complete, it will turn to cranking out the estimated 156 panels in the lower "through truss" section. That work is expected to continue until next summer.

Kolberg said that shipping the sections - aboard tractor-trailers that will themselves take a barge ride down the bay - is to begin about Sept. 15.

He said the authority expects the contractor to remove the old panels and install new ones at a rate of one a night, maybe two if the crews become extraordinarily proficient.

No rigid timetable

Unlike in the first phase, the contractor will not be held to a rigid timetable.

"We're letting the construction drive the schedule," Kolberg said.

The authority expects most closings of the westbound bridge this fall to begin between 8 o'clock and 10 o'clock on weekday nights, with the span reopening by 5 a.m. the next day. While the westbound bridge is closed, traffic will flow in both directions on the two-lane eastbound span. All lanes will be open during the morning and evening rush hours, and on weekends.

Deck-work target

The deck work - the first full replacement on the westbound span since it opened in 1973 - is expected to be completed in late 2009. The new deck should be good for 30 years, Kolberg said.

The authority plans to hold two "community outreach" meetings next week for people interested in the project.

The first will be held from 5 p.m. to 8 p.m. Tuesday at the Bay Bridge Automotive Shop, 881 Oceanic Drive in Annapolis, and the second next Thursday during the same hours at the Kent Island Volunteer Fire Department hall at 605 Main St. in Stevensville.

michael.dresser@baltsun.com

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