October 9, 1888 - The Washington Monument Opens

On this day in engineering history the Washington Monument was officially opened to the general public. This monument is one of the world's tallest masonry structures at 555 feet (169.29 m) and is made of marble, granite, and sandstone.

Robert Mills's original design called for a 600 foot decorated obelisk that rose from a circular colonnaded building 100 feet high and 250 feet in diameter. This temple was intended to be an American pantheon, a repository for statues of Presidents and national heroes.

Excavation for the foundation of the Washington Monument began in the spring of 1848. Its cornerstone was pure white Symington marble that weighed 24,500 pounds. The marble was laid on July 4, 1848 as part of an elaborate Fourth of July ceremony. The foundation extended from 7 feet, 8 inches below ground to 15 feet, 8 inches above ground.

By 1854 the obelisk had been built to a height of 152 feet. Continued growth allowed the monument to grow another four feet by 1856. This additional growth allowed the obelisk shaft to reach a height of 156 feet, 4 1/8 inches. The sides at the top of the obelisk averaged 48 ft, 9 and 5/8^th inches in length and had a wall thickness of 11 ft and 5/16^th inches. At this point, the shaft leaned 1 3/4^th inches to the north and had cost close to $300,000 (USD).

In 1856 a hiatus in construction occurred due to a lack of funds and the advent of the American Civil War. Construction resumed in 1879 under the direction of Lieutenant Colonel Thomas Lincoln Casey of the U.S. Army Corps of Engineers. Casey proved that the original foundation was incapable of supporting the projected height and weight of the monument. He redesigned the foundation, strengthening it so it could support a structure that ultimately weighed more than 40,000 tons. Today a difference in shading of the marble is visible at approximately 150 ft (45 m). This discrepancy clearly delineates where the initial construction ended from where it resumed.

The monument was not completed until 1884, almost 30 years after the original architect's death. The capstone was set on December 6, 1884, and the completed monument was dedicated on February 21, 1885. Upon its completion, the Washington Monument inherited the title of "world's tallest structure" from the Cologne Cathedral. It held this title until the Eiffel Tower was finished in Paris, France.

Washington Monument Statistics:

Total cost: $1,187,710

Height of monument above floor: 555 feet 5 1/8 inches

Width at base of shaft: 55 feet 1 1/2 inches

Width at top of shaft: 34 feet 5 1/2 inches

Thickness of walls at base of shaft: 15 feet

Thickness of walls at top of shaft: 18 inches

Depth of foundation: 36 feet 10 inches

Weight of monument: 90,854 tons

Sway of monument in 30-mile-per-hour wind: 0.125 of an inch

Sources:

http://www.nps.gov/archive/wamo/history/

http://www.tourofdc.org/monuments/washington-monument/

http://en.wikipedia.org/wiki/Washington_Monument