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#Post#: 735--------------------------------------------------
An OLD Invention that is always New!
DIR By: AGelbert
Date: December 26, 2022, 12:16 pm
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December 25 🎄, 2022 By Mark Bushnell
[center]Then Again: News flash — Covered bridges weren’t
designed to be quaint[/center]
If covered bridges didn’t already exist, the Vermont tourism
industry would have to invent them :D. What more quintessential
winter image can you create of Vermont, especially around the
holidays? All you need is snow and a covered bridge, and you’re
done.
But don’t judge a bridge by its cover. Covered bridges might
appear antiquated in the extreme, as if their sole remaining
purpose is to be quaint, but in fact they are one of those rare
innovations that even after centuries still perfectly fits its
original purpose. That’s because covered bridges weren’t
designed to be quaint; their quaintness was a byproduct of good
design.
Some people have the misconception that the purpose of a roof on
a bridge is to keep snow off it so it doesn’t have to be plowed.
That was actually an unfortunate consequence of the design, but
we’ll get to that in a moment.
The roof had — and still has — two purposes. The main purpose is
to protect the deck and the trusses (the triangular sections
that use a combination of tension and compression to support the
bridge) from the elements.
While wood is a comparatively light, cheap and strong building
material, moisture is the death of wooden structures. An
uncovered wooden bridge might last only a decade or two before
succumbing to rot. In contrast, a covered bridge can easily last
more than a century. (A shout-out here to the Pump Mill Bridge,
located on the Middlebury-Weybridge town line, which recently
began its third century of service, making it the state’s
oldest.)
Covering a bridge also offers a second structural benefit: The
roof actually reinforces the truss, allowing for construction of
longer bridges.
The Permanent Bridge
In early Vermont, when water
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/>power was king, communities naturally grew up beside a river,
brook or stream. Build a mill by some dependably running water
and you had a power source to make almost anything.
Bridges soon followed the mills, because they allowed towns to
grow on both sides of the waterway. These bridges did away with
isolation, and eliminated the need either to establish a ferry
service or take a time-consuming detour.
When a community could afford to, it covered its bridges. The
increased longevity was a good investment. Timothy Palmer,
designer of America’s first covered bridge, believed that
keeping the supporting trusses dry would add 40 years to a
bridge’s lifespan.
Palmer’s original covered bridge was constructed in Philadelphia
and dubbed the Permanent Bridge. Opening in 1805, the bridge
spanned 500 feet, with a nearly 195-foot-long center section.
Palmer, however, underestimated the added life a roof could
bring to a bridge. His Permanent Bridge operated for 70 years
and was probably structurally sound enough to last for decades
more. Its end came not by rot, but by fire.
A series of bridges spanning the Connecticut River between
Windsor, Vermont, and Cornish, New Hampshire, faced similar
challenges, though not from fire but from rising water.
The first bridge was constructed in 1795 by the Cornish man who
ran the local ferry service across the river. He apparently
decided that collecting tolls from the comfort of his home,
which sat on the New Hampshire end of the bridge, was preferable
to ferrying paying customers in all weather. ;D
The structure, a simple, wooden bridge, was wiped out by a
spring flood in 1824. Its replacement went up that same year,
but like the first was destroyed in a flood. The third bridge on
the site met a slightly different fate in 1866. This time the
water came in the form of ice, which lifted the span off the
abutments and sent it rushing downriver, where it smashed
against a railroad bridge. The impact knocked nearly 400 feet of
the lower bridge loose.
Ten hours later, the largely intact railroad bridge was seen
floating past Brattleboro, which was roughly 50 miles
downstream.
This was an important crossing, so construction of the fourth
Cornish-Windsor bridge started that same year. Remarkably, the
bridge company entrusted the same two builders who had
constructed the third bridge to build the fourth. Not
surprisingly, they altered the design, including raising it
higher above the river.
Confident that this fourth bridge would last long enough to rot
if not covered, the builders added a roof to it. Their
confidence was well placed; the span — at 450 feet, the longest
covered wooden bridge in America — is still in operation today.
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The Cornish-Windsor Bridge stretches 450 feet across the
Connecticut River, making it the country's longest wooden
covered bridge. Pieces of the span were laid out in a field in
Windsor by builders James Tasker and Bela Fisher before they
connected them over the river. The lattice truss arrangement
that underpins the bridge was originally patented in 1820. Photo
from Wikimedia Commons
AGelbert NOTE: In order to fit this forum format, I had to
position the following graphics differently than in the article.
I replaced phrases "At left", "At top right", and "At top right"
with "above" to describe the location of the following graphics.
[center]
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Above, the diminutive Braley Bridge in East Randolph, sometimes
called the Johnson or Upper Blaisdell Bridge, is less than 40
feet long.
[center][img
width=640]
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Above, the Slaughter House Bridge, built circa 1872, is in
Northfield Falls.
[center][img
width=640]
HTML https://i2.wp.com/vtdigger.org/wp-content/uploads/2022/12/Mosely-Bridge-610x407.jpeg?strip=info&w=1280&ssl=1[/img][/center]
Above, a winding, snow-covered road leads up to the Mosely
Bridge, which is sometimes referred to as the Stony Brook Bridge
for the stream it crosses in Northfield. Photos courtesy of John
H. Knox. For a gallery of Vermont landscape photos by John H.
Knox, click here
HTML https://www.facebook.com/people/Vermont-By-a-Vermonter/100044390350824/?sk=photos.
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Not just a bridge
Though a community could justify a covered bridge’s expense on
purely practical grounds, the structures served other functions,
as Vermont author Ed Barna noted in his 1996 book “Covered
Bridges of Vermont.”
When not being crossed, the spans could function as large,
albeit rather airy, public buildings. As such, they were
sometimes used for church suppers, political rallies and
meetings of the local militia.
They were also convenient spots for travelers to get out of the
weather, for children to play, and for companies to post
advertisements for their products. Ads for horse medicines were,
predictably, a common sight on bridge walls.
Courting couples out on a walk or drive also knew the value of a
covered bridge, as it offered them the chance to share a secret
kiss (hence the term “kissing bridges”).
For all their benefits, covered bridges came with a unique
maintenance cost. Each winter, the town had to pay for “snowing
the bridge.” Think of it as the opposite of plowing. Before the
advent of automobiles, people relied largely on horse-drawn
wagons for transport. When it snowed, they switched out their
wagons for sleighs, which could ride atop the snow instead of
digging into it.
At this point, however, covered bridges’ ability to keep snow
off the decking proved a liability. Sleighs need snow to glide
upon, so towns hired a local resident each year to keep the
bridge deck covered in snow.
The number of covered bridges in Vermont peaked in the late
1800s at somewhere between 700 and 800. There is no official
count. The number has declined significantly since. A 1941 issue
of the Vermonter magazine noted that the state then had roughly
160 covered bridges. That figure would have been significantly
higher if not for the Flood of 1927, which destroyed an
estimated 200 covered bridges.
About 100 covered bridges remain
Today, Vermont has roughly 100 covered bridges. And they remain
vulnerable to severe weather. More than a dozen were damaged in
2011 by Tropical Storm Irene, which swept away the Bartonsville
Covered Bridge in Rockingham. A community effort led to
construction of a new covered bridge in the same spot a year and
a half later.
As covered bridges disappeared, people started romanticizing
them. “Covered bridging” has become a verb, much as “leaf
peeping” has.
Through no fault of their own, covered bridges have inspired
their share of saccharine artwork, as well as hyperbole. Take
for example C. Ernest Walker’s writing in his 1959 book “Covered
Bridge Ramblings in New England”: “Throughout our nation the
robed figure of Liberty has been accepted as the emblem of
Freedom, and the solidly framed covered bridge might well be
selected as the symbol of its integrity.”
It is easy to make fun of how covered bridges have been depicted
over the years in sepia-tinted photos and purple prose. They
remain not only a testament to Vermont’s past, but also a
practical gift to its present.
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