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INFORMATION ABOUT COVERED BRIDGES



The first covered bridge to be built in the United States was located on Market Street in Philadelphia. Pennsylvania, and spanned the Schuykill River.  It was built in 1805.  It was quite a lengthy structure.  Shortly, thereafter, the second covered bridge in the United States was built, a 1,008 foot giant that crossed the Delaware River between Morrisville, Pennsylvania and Trenton, New Jersey.  The greatest period of bridge building activity took place in the United States from the 1820s to the end of the nineteenth century.  During this time period, there were at least 1500 covered bridges built in a variety of sizes and truss design.  

Why are covered bridges covered?   They may have been covered for many reasons.  The biggest reason was to protect the wooden structure from the weather.  Rain, snow, ice and the sun all make wooden bridges fail much faster.  By covering the wooden bridge, the bridge will last longer.  They are also covered to help get cattle over the bridge, the sight of the rushing water scar the cattle and make them hesitate going over the bridge.  It also helps prevent the cattle from stampeding across the bridge. Some towns used to fine people if their horses or cattle went over the bridge too fast, claiming it was damaging to the bridge.  They were also covered to keep the rain off the wooden deck of the bridge which would make it very slippery.  The roofs on covered bridges also kept the snow off the bridge.  It is also said that the roofs and walls on a covered bridge covered up the ugly trusses, and also provided shelter in bad weather.  Some people also claim that the reason why covered bridges are covered was that the roof and walls help strengthen the covered bridge, adding to the reason to cover a bridge.

THE COVERED BRIDGE NUMBERING SYSTEM -THE WORLD GUIDE NUMBER (WGN)

The covered bridge numbering system - World Guide Number (WGN) was devised by John Diehl of Cincinnati, Ohio.  The system has three numbers separated by hyphens.  The first number represents the number of the US state in alphabetical order, for example Alabama is number 01, Ohio is 35, and Wyoming is 50.  The second number represents the county in that state.  Adams County in Ohio is 01.  Each bridge in that county can them be sequentially numbered as additional bridges are built, like 02.  Therefore a bridge in Adams County Ohio would be 35-01-02.  When the first Would Guide to Covered Bridges was published, it adopted the same system and expanded it to include numbers for the Canadian Provinces, New Brunswick is number 55, Ontario is number 59 and Quebec is number 61.  Foot bridges are identified with a lower-case letter and bridges large enough to handle vehicles are given a capital letter, and bridges of interest are given a (A or (a depending if its a vehicular bridge or a foot bridge.  A footbridge in Adams County Ohio would be 35-01-a or 35-01-A depending on its capacity.  When a bridge is almost completely destroyed by fire or flood but are rebuilt to closely resemble the old bridge the are given a suffix of # 2, etc, is added to the bridge number to distinguish the new bridge from the old bridge.  A new bridge in Adams County Ohio would be 35-01-02 #2.


TRUSSES

KINGPOST TRUSS

This is the oldest truss design used in building covered bridges.  It consists of a stringer, a Kingpost (vertical beam), and two diagonals and is used primarily for a short span of twenty to thirty feet.

MULTIPLE KINGPOST TRUSS 

The Multiple Kingpost truss design was developed to span longer distances up to a hundred feet.  The design consists of one Kingpost in the center with several right angle panels on each side of the center.

QUEENPOST TRUSS

The Queenpost truss followed the Kingpost in design chronology.  It is used to span long distances up to 75 feet.  The Queenpost truss is an expansion of the Kingpost because of an additional rectangular panel in the center which is placed between the two triangles that faced the center vertical Kingpost timber. The upper horizontal member of that rectangle has to be placed below the horizontal upper chord of the exterior side framework.

BURR ARCH TRUSS

Theodore Burr from Terringford, Connecticut built a bridge spanning the Hudson River in 1804 and patented the Burr Arch truss in 1817.  His truss design became one of the more frequently used designs.  The Burr Arch truss uses two long arches, resting on the abutments on either end, that typically sandwich a Multiple Kingpost truss.

TOWN LATTICE TRUSS

Ithiel Town, who also came from Connecticut.designed and built his first bridge in 1820 using the Town Lattice truss.  After a glimpse at the pattern formed by its members explain its name.  It became very popular in some areas because it used smaller dimension lumber than other trusses, required a limited amount of framing  and hardware, easily be built by unskilled laborers, and could span distances up to 200 feet.  

HOWE TRUSS

William Howe of Massachusetts patented the Howe truss in 1840.  It is a elaboration of the Multiple Kingpost truss where by two heavy metal rods are used for the vertical timbers.  There is a variation that added a second diagonal timber to the original single diagonal fo the Multiple Kingpost and/or another diagonal timber running in the different direction between the vertical rods.

SMITH TRUSS

Robert J. Smith of Tippecanoe City, Ohio developed four truss systems.  None became popular.  The Smith truss, Type 2 was the only one of the four to receive a patent in 1867 and 1869.  There are three variations of the truss.

LONG TRUSS

Col. Stephen H. Long became the frist American to use mathematical calculations to develop a truss in 1830.  It is made entirely of wood instead of a combination of wood and metal.  It became known as the "X" truss, and he made further improvements patented in 1835 and 1837.

PRATT TRUSS

This truss was originally designed by Thomas and Caleb Pratt in 1844.  It is a transition from wood designs to metal.  The identifying features are the diagonal web members which form a v-shape.  The center section has crossing diagonal members.  This truss is practical for use when spans up to 250 feet long. 

PARTRIDGE TRUSS

Ruben L. Partridge received a patent in 1872 for his design of a truss that was close to the Smith truss design.

CHILDS TRUSS

Horace Childs developed the Childs truss in 1846.  It is a truss that simply adds diagonal iron rods to a Multiple Kingpost design.

WARREN TRUSS

In 1848, two Englishmen of Great Britain, James Warren and Willoughby Moinzoni pattened the Warren truss.  It uilizes isosceles triangles or many equilateral by the web members which connect to top and bottom chords.

WERNWAY TRUSS

Lewis Wernwag, a German designer, constructed a single span in 1805 of 340 feet long spanning the Schuykill River, a record of the day.  It was rumored that the bridge would collapse when the scaffolding was removed.  Mr. Wernwag removed the supports himself and it stood soundly for 26 years before being destroyed by fire

HAUPT TRUSS

Herman Haupt designed and patented his truss in 1839.  The truss concentrates much of its compressive force through the end panels and onto the abutments. 

PADDLEFORD TRUSS

Peter Paddleford worked with the Long truss system and eventually adopted it, but was unable to patent it due to challenges from owners of the Long truss patent.  The truss are remarkable in that the assembly of interconnected timbers require exceptional skill for a proper fit.  They behave more like frames than trusses, involving shoulder bearing at the frame connections with much of the resistance due to shear and bending stresses in the elements.

BOWSTRING ARCH TRUSS

Squire Whipple patented the Bowstring Arch truss in 1841.  It is similar in appearance to a tied-arch bridge, a bowstring truss is a truss and has diagonal load-bearing members.

BROWN TRUSS

Joseph Brown Jr., of Buffalo, New York patented it in 1857.  It is a diagonal cross compression member connected to horizontal top and bottom stringers and known for economic use of materials.

POST TRUSS

It is a hybrid between a Warren truss and a double-intersection Pratt truss.  It was invented by Simeon S. Post in 1863, nut no patent was ever received.


OLDEST EXISTING BRIDGE IN THE UNITED STATES  

That depends on who you ask about the oldest existing covered bridge in the United States.  There are three bridges with unconfirmed completion dates before 1830:  The Hyde Hall Bridge (WGN 32-39-01) in Oswego County, New York, circa 1825' Haverhill-Bath Bridge (WGN 29-05-04) at Woodsville, New Hampshire, circa 1829; and the Roberts Bridge (WGN 35-68-05) in Preble County, Ohio, built in 1829.       
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