The derricks pulled themselves up the curved legs of the Arch; their adjustable supports kept them level regardless of the height and curvature of the legs. Because the height made it impracticable for workmen to climb to and from the work area, the derrick platforms (43 X 32 feet) were reached by a passenger elevator and were equipped with a tool shed for workmen, sanitary facilities, and communications equipment.
Two vertical tracks held the sled that supported the derrick and platform. These tracks, made from 12 WF steel beams with cover plates on both sides, were spaced 24 feet apart. Each track was about 2 feet from the extrados of the Arch leg and was attached to brackets held by four high-strength steel bolts of 1-1/4 inches in diameter.
Four high-strength steel pins of 5-3/4 inches in diameter connected the sled to the tracks. The telescoping steel legs that extended between the outer corners of the platform framing and the lower part of the sled had pin connections at both ends. As construction progressed, and the curvature of the Arch increased, the telescoping legs were shortened to keep the derrick platform level. Sections of track were added in about 48-feet lengths, and the entire derrick crept up after it had placed four sections of the Arch. Lifting an Arch section into place took only about a half hour.
Did You Know?
The Gateway Arch at Jefferson National Expansion Memorial is 630 feet high and the span of the legs at ground level is 630 feet across. Click here to learn more about the Gateway Arch. More...