Hines soon determined the schedule and the museum's move-in priorities weren't clear. For one thing, LNJV's substantial completion date was July 15, 2011; however, the museum had decided it needed to occupy the administration building by April 1, 2011, to prepare for the opening. But LNJV had left that building for last because it was the simplest.

By May 2010, Hines and LNJV had developed a new sequencing plan. The biggest change was moving the administration building to the head of the critical path to allow LNJV to achieve the April date. “All of a sudden, buying toilet accessories and other mundane things became most important,” says Vavrek.

The new strategy worked. LNJV met the April 1 partial completion date and received a temporary certificate of occupancy for four more buildings on June 10. The armadillos and a gallery on the west side of the pond are just about done, which leaves the crab building and its neighbor to be completed on Aug. 15. Pond flooding is set for October. “The collaboration between Hines and LNJV is keeping the project on time,” says Bigelow.

Though all parties are mute on the project's cost, museum officials say it is on budget, with some change orders. There are no claims to date, they report.

In May 2005, when Walton announced the project and Safdie's selection, she also bought an 1849 painting called “Kindred Spirits” by Asher B. Durand. The scene brings to mind the Crystal Spring landscape—before crews disturbed 10 of its acres. To build a new home for the Durand painting and other art, crews blasted 190,000 tons of rock and removed 950,000 tons of material.

When Safdie first saw the site, it reminded him of the rugged landscape of ravines crossed by suspension footbridges he had seen a couple of months earlier during a trip to the Kingdom of Bhutan, near India. The suspended roofs might never have materialized had it not been for the trip, says Safdie. But for the Crystal Bridges museum, the architect's “suspension footbridges” are not made for walking: The reinforced concrete slabs of the armadillos and crab may look like bridge decks because of abutments and anchorages, but the slabs bear on concrete shear walls, not cables.

How Weir It Is

On a summer's day, Crystal Spring is usually 10 to 12 ft wide and 8 in. to one foot deep. In flash floods, the depth can swell to 8 ft and the width to 25 ft. The elevation drop from the cliff to the 8-ft-wide ravine bottom varies from 30 to 60 ft. The south-to-north flowing creek has a 700-acre drainage area.

CEI Engineering designed the pond system to accommodate a 500-year storm, plus a safety factor, so the buildings would never flood, says Massey. Stormwater relief is provided by the drainable ponds or through the creek's permanent diversion pipe.

CEI is using a labyrinth weir, which in plan resembles the outline of the teeth of a closed jack-o'-lantern's mouth, because its back-and-forth wall segments provide greater flow capacity than a straight-line weir. “If we had used a straight-line weir, the buildings would have been farther away from the water,” says Massey. CEI designed the weir with engineer BH.

In the pond design, water enters the site and flows into the 150-ft-wide upper pond before it hits the first weir under the 133-ft-long armadillo. It then spills over the weir through the 3.5-ft space between the weir and the armadillo's slab and enters the lower pond. Water then flows toward the second weir, topples over the weir under the 185-ft-long armadillo into a third, smaller pond before it re-enters the creek bed. Water in each constructed pond will be 6 to 8 ft deep; the armadillo slabs are another 6 ft above that.

The weirs were put to the test in April during a downpour. They did very well, even though at least one weir section was missing from each, says Massey.

Structurally, the cable-roof buildings, including the 11,092-sq-ft armadillo, the 6,604-sq-ft armadillo and the 5,275-sq-ft crab, are fairly similar, says BH's Correa. Pairs of 4-in.-dia steel cables, separated by braced glulam arches, span in tension between opposite abutments. BH devised a universal ball-and-ring socket to accommodate the angular variation between each arch end and the cable, both as the cable is being loaded and permanently. Many other connections adjust because of the varying geometry. Roof cladding provides a structural diaphragm.

The suspension system carries dead load. Structural-steel mullions carry live load, sloping in from roof edges. Mullions have a pinned detail top and bottom to allow rotation to accommodate side sway. Sloped glazing completes the envelope.