Special Reports

Bridge update: March 4, 2007

Construction this week on the new Tacoma Narrows bridge:

Crews pasting and wrapping the main cables have refined their techniques to deal with wet weather and are beginning to make good progress.

As of Friday, 12 of 270 “bays” had been wrapped. (A bay is the approximately 40-foot space between suspender hangers. Each takes 3.3 miles of wrapping wire.)

This week all four wrapping machines will operate – two near the top of the Tacoma tower, working their way down toward the anchorage, and two at the Gig Harbor anchorage, working their way up.

Most of the bolting needed to permanently join the 46 deck sections will be finished this week. That will leave only the bolts on some diagonals and those on the U-ribs that support the top deck plates. The U-rib bolts can’t be permanently tightened until the top plates are welded together.

The welding crews are forging ahead. At the end of last week they had finished 15 of 45 joints.

Crews installed gantries over the 24th Street on-ramp to the bridge in Gig Harbor last week to accommodate transponder-reading devices for the “Good to Go” automatic toll-collection system.

This week, they’ll install electrical conduit lines and electronic hardware at the gantries.

Why is the deck of the new bridge higher in the middle than the old one? – Karen P., Gig Harbor

The two decks weren’t designed to match precisely. They’ll be closer to the same level when the new one is paved. Paving material will constitute 15 percent of the total weight of the deck.

Rob Carson, The News Tribune