Why Were Covered Bridges Built?
A covered bridge is a timber-truss bridge with a roof and siding which, in most covered bridges, create an almost complete enclosure. Covered bridges were once common in the United States. Only a few Remain, they look like wooden tunnels, and were built during the days of the horse and buggy.
Some people think that the bridges were covered so that the horses would not be frightened while crossing the bridge and protecting pedestrians shying away from water. Actually, the roof and sides sheltered the bridge from snow and rain and protected the wood in the bridge from rotting. Uncovered wooden bridges have a short lifespan because of the effects of rain and sun.
Bridges having covers for reasons other than protecting wood trusses, such as early timber covered bridges consisted of horizontal beams laid on top of piles driven into the riverbed. The problem is that the length between spans is limited by the maximum length of each beam. The development of the timber truss allowed bridges to span greater distances than those with beam-only structures or arch structures, whether of stone, masonry, or timber.
Early European truss bridges used king post and queen post configurations. Some early German bridges included diagonal panel bracing in trusses with parallel top and bottom chords. To solve the problem of deterioration of the wood upon exposure to weather, various forms of covering came to be employed.
You can find covered bridges still standing in Vermont and several other states. Covered wooden bridges are no longer being built. Most bridges are now made of concrete or steel.