Saturday, May 26, 2007

New Covered Bridge Opens in Union County

This new covered bridge may appear all wood but the truss it utilizes is a combination of wood and steel. This is not a new innovation as many old covered bridges used a combination of iron or steel and wood in their truss. Most notably - and probably the best CB truss - the Howe truss used metal as an adjustable vertical tension member. As metal got cheaper wood was done away with altogether in the truss, which meant the wood roof was no longer necessary to protect it from rotting and covered bridges became history!

John Smollen, former County Engineer of Ashtabula county is leading a minor rebirth by building several new wood CBs in Ohio, which he argues can outlive some modern materials. These are not replicas of historic CBs but utilize a modern variant of a Pratt Truss of his design. A Pratt truss was rarely used in all wood bridges because wood is less suitable for use under tension as required in the long (diagonal) members of this truss. The Pratt truss did come to dominate in metal bridges because metal is better suited for tension loading.

Now if we just had a similar champion for iron truss bridges.

Monday, May 14, 2007

Wheeling Suspension Bridge

Photo 5/2007

Not really Ohio (but close) this was the longest suspension bridge in the world at 1,010 ft when built in 1849 and is the oldest such bridge in service in the country. It spans the east channel of the Ohio River from Wheeling Island to Wheeling WV. Its deck was blown away in 1854 in much the manner the Tacoma Narrows suspension bridge was in 1940. It was quickly rebuilt with a truss reinforced deck to prevent future wind damage. This lesson apparently was lost on the designers of the Tacoma bridge!

Tuesday, May 08, 2007

National Road S-bridges

New Concord S-bridge
Guernsey County S-bridge

Blaine S-bridge & Blaine Hill Viaduct

They are not metal but eastern Ohio is home to these three restored masonry arch S-bridges on the Old National Road (later Rt 40). The Blaine bridge is the oldest in Ohio (1828) and is part of a trio of adjacent bridges two of which are visible in the lower picture. The S-bridge carried the National Road and is now closed to traffic. The Viaduct seen in the background carries Rt 40 and just behind it (not visible) is another bridge that carries I-70.

The bridges are S-shaped so that they cross the waterway with the shortest span.