Wayne,
The bulk of these "covered bridges" were built during the middle to late
1800's. Nearly all are truss bridges (using various truss designs) with a
"barn" built over them.
Reason for the "barn" part:
In the middle and late 1800's, steel was a premium, short in supply (in the
U.S.), much of it being used for rail, and little (if any) for structural
use such in bridges or buildings. Many smaller bridges were made of wood;
enormous wood beams (often laminated). The alternative, stone block, was
very costly. There wasn't much in the way of paint then either . . .
whitewash and "milk" paint . . . which did little to protect wood very
long. If the wood structural members were left exposed to the weather, as
many were in the late 1700's and early 1800's (in the U.S.), it rotted
within a few years. It didn't take long to figure out it was easier and
cheaper to replace barn siding and roofing than the large beams used for
the structural members.
Most are single spans supported only at the ends. The impressive part of
these bridges is the massive structural truss made entirely of wood hidden
from view by the siding. If you look closely at the walls, they do not
extend all the way to the roof. There is good reason for this too. It
didn't take long to figure out a 100-200 foot (30-60 meter) long barn with
openings only at the ends could get mighty hot inside during the summer.
The gap between the top of the wall and the eave of the roof allows heated
air inside the bridge to escape by convection. Many longer bridges have
windows with eaves over them which helped also. Most of these surviving
bridges in Indiana have been moved from their original locations to nearby,
very lightly traveled "section line" roads to preserve them.
-- John
At 05:12 6/17/00 , Wayne Harridge wondered:
>John wrote:
>
>>
>> Does this look anything like what you found with 3 ton weight
>> limit? It
>> was miles from the nearest *State* Highway on a county
>> section line road.
>>
>http://members.xoom.com/_XMCM/johnlind/olympus/olympusgallery/om57.html
>
>Just an aside, what is the reason for putting a roof on a bridge ?
>
>Wayne Harridge
>Ivanhoe, Victoria, Australia
>http://www.geocities.com/wayneharridge/
>
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