BAY BRIDGE -- Sometimes you have to think inside the box.

When architects designed the new Bay Bridge, they drew slender, white, side-by-side decks hanging from gently draped cables over the water as if by magic.

That left Caltrans engineers with a challenge worthy of David Copperfield: Where do you hide the anchorages for the world's longest self-anchored suspension span?

Domineering, chunky piers were out of the question both for aesthetics and cost. The architects blanched at slapping onto their svelte bridge a monstrous, multistory anchorage housing.

If you cannot go down or out, you go inside.

Pushed by the architects, engineers compressed the anchorages into the "The Box," shorthand for the interior of the span's side-by-side hollow steel bridge decks. Only a trained eye can see where the decks jut out slightly into a nearly invisible wedge discernible from beneath the bridge.

It was a true marriage of engineering and aesthetics, said the project's chief engineer and architect.

"Many engineers, bless their souls, don't have a good sense of proportion," said Bay Bridge project architect Donald MacDonald of San Francisco. "That's why the greatest bridges in the world have architects involved."

"People asked me again and again after the design was approved (in 1998), 'Brian, is it buildable?'" said Caltrans bridge engineer Brian Maroney. "The answer was yes. But the question should have been, 'How will you build it?'"


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Explaining the "how" to non-engineers is best done through show-and-tell.

In what may be the final outsiders' descent into the anchorages before they are closed under post-Sept. 11 national security protocols, Maroney led a Bay Area News Group reporter and photographer deep into "The Box" for a firsthand look.

Clambering down ladders, ducking through rounded doorways and clicking along the grated walkway under artificial yellow light feels like below-decks in a big ship.

"The Box" is actually two side-by-side steel shells running underneath the 2,047-foot suspension span roadway built from 28 segments fabricated in China, barged to California, lifted into place with crane and welded together.

Inside, it looks like Ikea build-it-yourself-furniture on steroids -- the thousands of differently shaped steel plates bolted in a variety of geometric patterns onto the walls, floors and ceilings must have given ironworkers vertigo.

The boxes are orthotropic, meaning they contain steel stiffeners that run in multiple directions. This deck type is lighter, and the reduced weight helped engineers constrain the anchorages' size to fit within the bridge's narrow profile, Maroney said.

It took three quarters of an hour walking up and down stairs and through hatches below the roadways to reach the westbound anchorage entrance as Maroney and his colleagues stop and point to one and then another construction detail.

Once inside the dimly lit inner sanctum, there is a church-like hush.

Only the cable-draped 525-foot tower rivals the anchorages when it comes to bearing the weight of this 77.6 million-ton bridge.

A self-anchored suspension span is just what its name says: The suspension cable ties back into the bridge, and the combined forces of weight and compression allow the span to hold itself up.

On the new Bay Bridge, the 1-mile-long cable wraps sling-like around its western end at Yerba Buena Island. The two sides of the cable then rise to the saddle atop the tower before they descend and split into their respective anchorages.

Standing inside the anchorage and looking straight up at its two-story wall, each of the cable's 137 steel strands poke through a strategically placed bore hole.

Chunky steel blocks and nuts big enough to put a child's hand through secure to the wall each hand-numbered strand.

Aligning the holes and strands was like playing "Whac-A-Mole," Bay Bridge project manager and engineer Ken Terpstra said. "Just when you got one lined up, another one would go out of place."

Later, American Bridge/Fluor project director Brian Petersen, whose company is building the suspension bridge, summed up the project's sheer complexity this way.

"I've worked at Cape Canaveral for NASA," Petersen said. "But building this bridge makes launching rockets look easy."

It's so fascinating, it's hard to pull away, but the best is yet to come.

An unexpected lull in the construction means the small troupe is allowed to cross onto the other side of the anchorage wall and shimmy on their bellies deep into the splay chamber.

This is where the single 2.6-foot-diameter steel cable splits, or splays, into the 137 wire bundles needed to spread the nearly unfathomable weight load into more manageable units.

We crawl straight into a cold steel web of 2½-inch thick strands like Lilliputians exploring a the guts of a grand piano.

Here, the bridge feels alive. Her steel hums and vibrates beneath our fingers.

It is physics, not biology, of course.

As Maroney explains, the bridge expands and contracts several inches each day as the air temperature rises and falls.

Still, the humans grow giddy, knowing they are among the few who will ever stand in this place and feel a bridge breathe in and out as though it were a living thing.

Contact Lisa Vorderbrueggen at 925-945-4773, lvorderbrueggen@bayareanewsgroup.com, politicswithlisav.blogspot.com or Twitter.com/lvorderbrueggen.

vitals: NEW BAY BRIDGE

Construction began -- 2002
Statistics -- The 1.6-mile state-owned span is actually two bridges tied together and sandwiched between complex elevated connector structures: The 1.2 mile side-by-side skyway curves westward from Oakland toward Yerba Buena Island, where it links with the 2,047-foot self-anchored suspension span, the longest in the world.
Cost -- $6.42 billion, the largest public works project in California history.
Main construction contractors (partial list) -- American Bridge/Fluor Enterprises, Kiewit/FCI/Manson
Designers (partial list) -- T.Y. Lin/Moffatt Nichol Engineers, Donald MacDonald Architects,
Opening date -- Labor Day 2013