What Col. Thomas Casey found in 1876 when given the daunting challenge of completing the Washington Monument was shocking. The 46-year-old U.S. Army Corps of Engineers structural engineer was presented with the beginnings of a colossal marble-faced masonry pillar with significant flaws. Proposed as a glorious tribute to the nation’s first president and envisioned as the tallest masonry obelisk in the world, the incomplete monument had stood neglected for nearly a quarter of a century — a national disgrace.
Even though it was less than one-third of its projected 600-foot height when Casey took over, the square masonry pillar (shaft) was already exerting more than 10,000 pounds per square foot (psf) of pressure on fragile supporting soils. It leaned 1.7 inches out of plumb and sported alarming cracks, chipping, and spalling in its marble skin and masonry near its base, as well as inferior masonry work at its top. And there was considerable concern about its footings and overall structural integrity.
Would America be embarrassed internationally by erecting a fiasco — a 19th century “Leaning Tower of Pisa?” Not with the daring Casey having absolute control!
Planning an appropriate memorial to George Washington began in 1832, the 100th anniversary of the first president’s birthday, with the forming of the Washington National Monument Society led by James Madison and John Marshall. Although donations for the project were initially sluggish, the society moved ahead, believing the sight of a memorial being built would generate unbridled support and funding.
First came a design competition won by American-educated engineer/architect Robert Mills (1781-1855), a one-time draftsman to Thomas Jefferson and the designer of the U.S. Treasury, Patent Office, and General Post Office facilities. His entry called for a narrow, 600-foot-tall, flat-topped masonry pillar surrounded by a massive circular colonnade at its base with an imposing sculpture of Washington in a chariot on its roof. Its price tag was $1 million ($22 million in today’s dollars). That cost had its critics. So did the design’s ostentatious base colonnade sprouting a skinny central shaft that appeared chopped off at the top.
The society nonetheless pushed forward. On July 4, 1848, the memorial’s cornerstone was laid by President James Polk in an elaborate ceremony attended by several dignitaries including Abraham Lincoln. From the very beginning, the shaft’s foundations were severely compromised. U.S. Treasurer Elisah Whittlesey (1783-1863), a lawyer and comptroller for the project, said the building committee and the board of managers believed the original footing, only 80 square feet bearing on a compressible bed of clay and fine sand (8 feet below the surface), was safe enough. It would have resulted in the completed shaft exerting a dead-load base pressure of approximately 19,000 psf!
Construction came to an abrupt halt in 1856 from lack of funds, support, and direction. Then, after celebrating the Centennial of Independence in 1876, President Ulysses Grant approved appropriations to complete and maintain the monument — if Casey could salvage what had been built, streamline the design, and make it structurally stable. He quickly fixed the masonry and marble skin-panel problems and redesigned the monument to resemble a sleek Egyptian obelisk with a pointed pyramidion. However, salvaging and strengthening the masonry foundation was another matter.
Imperative was giving additional spread to the as-built footings and carrying them down to a solid stratum of boulders and gravel. Casey engineered a modified foundation system with two and a half times the original area, extending 13-1/2 feet deeper.
As the monument reached completion on Dec. 6, 1884, Casey ceremoniously placed a rare 100-ounce aluminum tip onto its 3,300-pound capstone, bringing its height to 555 feet, 5-1/8 inches — the world’s tallest masonry monument.
Officially dedicated Feb. 21, 1885, and opened Oct. 9, 1888, the soaring marble-faced structure resembled a classical obelisk with its height 10 times its base width. It towers over everything in the national’s capital, a reminder of Washington’s immense contribution to the republic and a vivid example of what structural engineers can accomplish when fully in charge.
Richard G. Weingardt, P.E., is CEO and chairman of Richard Weingardt Consultants, Inc., a Denver-based structural engineering firm. He can be reached via e-mail at email@example.com.