Ten earth-covered missile assembly buildings built at K.I. Sawyer Air Force Base in Michigan's upper peninsula presented the contractor with scheduling and forming challenges. The massive 112x46-foot concrete buildings had heavily reinforced walls 3 feet thick at the base, tapering to 2 feet at the top. The 40-foot-span arch roof needed shoring to remain in place until the concrete became self-supporting.
With about 550 cubic yards of concrete in each structure, a 2-foot limit on lifts, and an absolute prohibition of cold joints, progress was slow and costly on the first two buildings. When the remaining eight missile assembly buildings were to be built, the contractor for this second phase consulted formwork specialists. The form supplier designed and built formwork that made it possible to simplify and speed up construction. Efficiency depended on two basic ideas:
- Reduce the size of the pour--Instead of casting each 112-foot-long building in only two 56-foot sections, use smaller forms and place concrete for the building in four 28-foot sections.
- Make the inside form in three pieces--Instead of the single U-shaped form tried in Phase I, use two L-shaped forms and a narrow center form which stays in place with its shoring support after the L-shaped forms are stripped.
This approach enabled the contractor to eliminate most of the overtime and waiting time. Each pour could be completed in 6 1/2 hours. Outside wall forms could be stripped the second day after casting, and the two inside L-shaped forms could be stripped the third day as soon as the concrete reached 2000 psi.