The world’s then longest suspended span, the Wheeling Suspension Bridge, at Wheeling, Virginia (now West Virginia), was destroyed by wind in 1854. Designed by Charles Ellet, Jr. in 1847, it had been constructed in 1849 (Pic. 1). On May 17, 1854, a severe windstorm swept up the Ohio River, destroying the bridge. Wheeling’s newspaper, The Intelligencer, described the collapse (Kemp 1997);
Pic 1.Drawing of Ellet’s Wheeling Suspension Bridge, built in 1849, before its collapse under high winds (HAER 1984)
. . . we watched it with a breathless anxiety, lunging like a ship in a storm; at one time it rose nearly the height of the tower, then fell, and twisted and writhed, and was dashed almost bottom upward. At last there seemed to be a determined twist along the entire span, about one-half the floor being nearly reversed and down went the immense structure from its dizzy heights to the stream below with an appalling crash and roar.
There were 50 cm (20 in) of snow on the ground and winds gusting up to 72 km/h (45 mph) on a December night in 1876, when a cast and wrought iron bridge collapsed into the Ashtabula River in Ohio, taking with it a passenger train (Simmons 1985). Ninety-two people were killed. The bridge at Ashtabula was a Howe truss that had been built 11 years earlier. While moderate wind velocity contributed to the collapse, the Ashtabula disaster did not initiate a discussion on wind pressure. Material and construction problems were identified as the main causes. The Ashtabula disaster shook the American engineering community. A public outcry launched investigations. The construction weekly Engineering News filled with articles describing the collapse,
reports on the investigations, editorials, and opinion contained in letters to the editor.
Review of the periodical’s issues (Rutz 2004) reveals a huge interest in the collapse throughout much of the subsequent year 1877. A new demand for engineering specialists responsible for public safety—consultants—rather than employees of bridge manufacturers came about. Three years later the crossing at the Firth of Tay in Scotland— the Tay Bridge—collapsed in a windstorm. A train plunged into the water below; none of its 75 passengers survived. Lack of lateral bracing to accommodate the severe wind is blamed for the Tay Bridge collapse of 1879, shown in Fig. 4. As was the case with Ashtabula, a response to the Tay collapse is documented in issues of Engineering News seemingly throughout the year 1880.
The designer of the Tay Bridge, Thomas Bouch, made insufficient allowance for wind load. He was in possession of a report from Astronomer Royal George Airy regarding winds to be expected at the estuary to the south, the Firth of Forth. Airy, writing from the Greenwich Observatory, reported that the entire structure would experience a pressure of 480 Pa (10 psf), although “for very limited surfaces, and for very limited times, the pressure of the wind does amount to sometimes 40 lb. per square foot” (Petroski 1995). It is to be noted that the high girders for the replacement bridge were designed for 2.68 kPa (56 psf) wind pressure (Petroski 1995). Investigations of these disasters brought lessons to light (Watson 1975):
- The use of cast iron was abandoned altogether.
- The railroads realized that reliance on the bridge companies alone was insufficient; specialists in bridge construction were needed.
- Procedures for material testing and quality control were introduced and studies of wind bracing were made.
Smith calculated the wind pressure as that necessary to “produce the observed effect.” Thus the actual wind pressure must have been at least that, but probably greater. Smith did not state his failure criteria.
Tay Bridge, Before Collapse
Tay Bridge, After Collapse
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