Defying gravity

The roof of the Kingdome is the largest concrete dome in the world, spanning 660 feet. It is held up by a balance of pressure between its inner and outer rings the compression ring in the middle anchors the tops of the ribs, while the encircling tension ring keeps the ribs' bases in place.

The key to the implosion is to release this pressure by breaking the ribs in the middle. When this happens, most of the structure should collapse inward.

Compression ring
Anchors ribs in the center of the roof. It pushes down on the ends of the ribs, which in conjunction with the inward pressure exerted by the tension ring creates the arch in the ribs that supports the weight of the roof. The 28.8-foot wide, 7.5-foot thick plug will be broken up in the second phase of the implosion and will fall on a 25-foot cushion of crushed concrete below.

Tension ring
Keeps ribs from sliding outward. The 25-foot wide, 2-foot thick ring is composed of multiple lengths of steel cable encased in concrete. Since the cables won't break during the implosion, they will help keep debris within the footprint of the Kingdome.

Dome statistics
Building area:	9.34 acres
Roof area:	7.85 acres
Height:	250 feet
Diameter:	660 feet (inside wall)
	720 feet (exterior walls)
Volume:	67 million cubic feet
Exhibit space:	190,400 square feet
Weight:	130,000 tons
Structural steel:	443 tons
Concrete:	52,800 cubic yards

Graphics and text: Phil Loubere; Reporting and text: Whitney Stensrud; Reporting: Jeff Hodson / © 2000 The Seattle Times

Copyright © 2000 The Seattle Times Company