What We Build

May/June 2008

A Bold Approach

Seattle keeps Fremont Bridge open during entry-replacement project

By Sheila Bacon

Seattle’s Fremont Bridge remained open to traffic while the bridge’s elevated approach structures were replaced. In this August 2006 aerial, the entire east half of the approaches were completely formed, with rebar installed, as crews awaited the end of a month-long regional concrete workers’ strike. (Photo Courtesy of Soundview Aerial Photography)

When planning began to replace the elevated approaches of the 319-ft-long Fremont Bridge in Seattle’s Fremont neighborhood, it quickly became clear the job would be anything but typical.

As one of the main entryways to a popular and quirky neighborhood that dubbed itself “The Center of the Universe,” the bridge needed to remain operational during construction, allowing to proceed, among other things, the dozens of festivals, parades and seasonal functions that intermittently turn the already popular locale into a crowded party zone.

The 91-year-old Fremont Bridge is a bascule-type drawbridge, a movable structure with a counterweight that continuously balances the span throughout its entire upward swing. It spans the man-made Lake Washington Ship Canal, a corridor for ships passing between Lake Washington and the Puget Sound. It opens to marine traffic up to 35 times each day in the summer and handles 33,000 vehicle trips and 1,200 bicycle trips daily. Two pedestrian paths cross beneath the elevated approaches, and office buildings are located within feet of the north approach on both sides.

There were thoughts early on about closing the bridge during construction of the approaches, “but those didn’t last long,” says Lorelei Williams, project manager with the Seattle Dept. of Transportation.

When faced with the possibility of a two-year, full-bridge closure, the tight-knit Fremont business community appealed to Seattle’s mayor to find additional funds, says Einer Handeland, project manager with the Seattle office of Parsons Brinckerhoff, the job’s design consultant. The community also came up with funds of its own to help offset the cost of performing the work in pieces—a process that added nearly a year to the job but kept half of the bridge open to traffic during the rehabilitation.

Demolition of the existing approaches was done carefully to ensure debris did not fall into the Lake Washington Ship Canal below. (Photo Courtesy of Seattle Dot)

“It’s not very often when a community comes together and offers those kinds of things,” says Handeland, who was involved in the planning process from the beginning. “It really made an impact on the decision-makers.”

Stakeholders felt that full closure of the bridge would not only impede access to the coffee shops, restaurants, clothing stores and other businesses in the tourist-friendly neighborhood but also would increase traffic on the few crossings elsewhere along the ship canal.

Owner-initiated planning efforts to keep business owners, residents, motorists, bicyclists and other bridge users informed of the job’s progress included open houses, newsletters, media releases, a dedicated project Website and frequent meetings with the businesses most affected. The city also hired a liaison to keep in constant contact with the Fremont business community during the project.

The $38-million project was divided into two major parts: the replacement of the 500-ft-long north and 150-ft-long south elevated concrete bridge deck approaches, followed by the restoration of the bridge’s original mechanical and electrical drive mechanisms. AGC member Mowat Construction Co., Woodinville, Wash., was the job’s general contractor.

Mowat crews removed the old bascule bridge’s gears and motors before replacing the system with four new drives, each weighing 26,000 lb. (Photo Courtesy of Seattle Dot)

Mowat crews started work in September 2005 with construction of new pilings, footings, columns and the lower halves of piers beneath the north and south approaches. Because the bridge was required to stay open, the contractor drove 8-in. micropiles to their required 80-ft depths. Augured piles were used because vibratory driving was prohibited due to the close proximity of high-tech businesses. The 14-ft drilling rig also fit neatly in the constricted site. Once work was completed nine months later, traffic was diverted to the west half of the bridge and approaches, while crews demolished and rebuilt the east half.

When the east half had been completed, traffic was shifted back to allow the west half to be demolished and rebuilt. The new approach structures are a combination of designs using cast-in-place concrete columns rising to 22 ft and 25 ft, with concrete girders and a concrete deck, thickened slabs and steel girders with a concrete deck.

The bridge remained open to light vehicles, bicycles and pedestrians during the bulk of the work, closing only for one weekend day and a handful of scheduled nights. Trucks and buses were rerouted.

Meredith Daniels, Mowat’s project manager, says unforeseen conditions at the north end of the bridge nearly halted one part of the job when as-built plans failed to show a below-grade parking structure directly beneath the planned location of one of two cranes that would be used in tandem to place a section of 120-ft-long girders.

That discovery nixed the use of the second crane. However, the largest crane available at the time—a 550-ton crane—was not robust enough to complete the pick on its own. Work threatened to screech to a halt.

Fortunately for the contractor, a new 650-ton hydraulic crane that was waiting to be sent to the Tacoma Narrows Bridge jobsite (Constructor Sept./Oct. 2007 p. 64) by Sicklesteel Cranes Inc., Mount Vernon, Wash., became available and was powerful enough to perform the solo pick.

“We had to completely rework the erection scheme and had absolutely no solution until we found out about Sicklesteel’s new crane,” Daniels says. “As it was, we needed full counterweight and the superlift to make the pick, and we shoehorned the crane into the site. It had only inches to spare for its counterweight to swing and was set within 3 ft of several walls and the new bridge piers.”

Once approach construction was complete last spring, all lanes were reopened to traffic and the behind-the-scenes work began. The mechanical and electrical portion of the job included replacement of motors, controls and electrical systems that open and close the bascule bridge, as well as new navigational lights and a new locking mechanism between the two bridge leaves.

The Mowat project team dropped from 80 members to just 12 for the smaller scope of work, but that didn’t mean the job was any less intense. The four new gear boxes—two for the south bridge leaf and two for the north—weighed 26,000 lb each and required extreme coordination to move them into place.

Crews erect girders at the Fremont Bridge’s north approach.(Photo Courtesy of Seattle Dot)

Their final locations in out-of-the-way alcoves meant the heavy machinery had to follow a circuitous route. Mowat crews installed steel beams across the bridge’s subgrade bascule pit and attached overhead cranes to move the gear boxes through small openings in the side of the bascule pier.

The boxes were then lowered into the pit, moved across it on rollers and raised back up with another set of overhead cranes. Then they were slid into place.

To operate the bascule bridge for marine traffic while the new system was being installed, Mowat crew members became temporary bridge tenders. They used a temporary winch and electric motors to open and close the side of the bridge they were working on, while the other side was operated by city workers.

Project team members knew they had met the stringent requirements set forth by the city when, at the substantial completion ceremony for stakeholders on Feb. 29, they were each given a commemorative Fremont Bridge project baseball cap with the following phrase stitched on the back:

"Keep it open,' they said — so we did. "

(Photo Courtesy of Seattle DOT) Fremont: The Center of the Universe Fremont is a popular, fast-growing residential and commercial Seattle neighborhood with dozens of off-beat shops, cafes and bars that have made it a popular gathering place. Formerly an industrial neighborhood in decline, Fremont has been experiencing a resurgence in recent years, especially along the Lake Washington Ship Canal, where a number of office buildings have been developed. The area has recently seen construction of new apartments and condominiums, and companies such as Adobe, Google and Getty Images have offices there. The eclectic residents—the majority of them artists—call themselves “Fremonsters,” and a sign at a central intersection claims Fremont as “The Center of the Universe.” A 16-ft-tall bronze statue of Vladimir Lenin mocks pedestrians at one of the main intersections, and the popular annual Solstice Parade features, among other things, hundreds of naked bicycle riders. The neighborhood is home to about 13,000 people north of downtown Seattle. June’s Solstice Parade draws between 40,000 and 50,000 people to the neighborhood, and the popular Oktoberfest celebration draws about 15,000 people over a weekend celebration. A weekly outdoor cinema in the summer hosts 1,500 people each night, and the year-round Fremont Sunday Market can draw up to 5,000 visitors on a sunny Sunday.