Trestle
Encyclopedia
A trestle is a rigid frame used as a support, especially referring to a bridge composed of a number of short spans supported by such frames. In the context of trestle bridges, each supporting frame is generally referred to as a bent
. Timber and iron trestles were extensively used in the 19th century, the former making up from 1 to 3% of the total length of the average railroad. In the 21st century, steel and sometimes concrete trestles are commonly used to bridge particularly deep valleys while timber trestles remain common in certain areas.
Many timber trestles were built in the 19th and early 20th centuries with the expectation that they would be temporary. Timber trestles were used to get the railroad to its destination. Once the railroad was running, it was used to transport the material to replace trestles with more permanent works, transporting and dumping fill around some trestles and transporting stone or steel to replace others with more permanent bridges.
In the later 20th century, tools such as the earthmover
made it cheaper to construct a high fill directly instead of first constructing a trestle from which to dump the fill. Timber trestles remain common in some applications, most notably for bridge approaches crossing floodways, where earth fill would dangerously obstruct floodwater.
on the Lucin Cutoff
in Utah
. It was replaced by a fill causeway
in the 1960s, and is now being salvaged for its timber.
Many wooden roller coaster
s are built using design details similar to trestle bridges because it is so easy to make the roller coaster very high. Since loads are well distributed through large portions of the structure it is also resilient to the stresses imposed. The structure also naturally leads to a certain redundancy (provided that economic considerations are not overly dominant). Such wooden coasters, while limited in their path (not supporting loops), possess a certain ride character (owing to structural response) that is appreciated by fans of the type.
The Camas Prairie Railroad
in northern
Idaho
utilized many timber trestles across the rolling Camas Prairie. The major trestle across Lawyers Canyon was the exception, constructed of steel.
, timber trestles were relatively short-lived as a structural type, one of their major uses being to cross the many deep valleys in Cornwall
on the spinal rail route through that county. These were all replaced by masonry viaducts.
So few timber trestles survived into the 20th century. Two that did, and which are still in daily use, cross the Afon Mawddach on the coast of Wales
only a few miles apart, at Barmouth
and Penmaenpool
. The former, built in 1867, carries trains on the heavy rail Cambrian Coast Line travelling from England via Shrewsbury to the various small towns on Cardigan Bay
. It also carries a toll-path for pedestrians. Road traffic at this location has to travel many miles around the estuary to cross at either (for light traffic) the second trestle bridge, at Penmaenpool, which is a toll bridge; or (for heavy traffic) at Dolgellau
even further up the estuary.
. These generally carried decking consisting of some form of trussed girder, as at Crumlin Viaduct, Belah, and Meldon; though two rare examples, at Dowery Dell
(demolished in 1962), and Bennerley
had lattice girder
decks.
are steel trestles.
New Orleans utilizes steel
trestles to support parts of I-10
, the Pontchartrain Expressway
, and Tulane Avenue
. Also, trestles support the elevated railroad leading to and from the Huey P. Long Bridge.
Bent (structural)
A bent is a framework composed of several structural members that defines the cross-section of a timber frame building or supports a trestle. The term bent is probably an archaic past tense of the verb to bind, referring to the way the timbers of a bent are joined together...
. Timber and iron trestles were extensively used in the 19th century, the former making up from 1 to 3% of the total length of the average railroad. In the 21st century, steel and sometimes concrete trestles are commonly used to bridge particularly deep valleys while timber trestles remain common in certain areas.
Many timber trestles were built in the 19th and early 20th centuries with the expectation that they would be temporary. Timber trestles were used to get the railroad to its destination. Once the railroad was running, it was used to transport the material to replace trestles with more permanent works, transporting and dumping fill around some trestles and transporting stone or steel to replace others with more permanent bridges.
In the later 20th century, tools such as the earthmover
Wheel tractor-scraper
In civil engineering, a wheel tractor-scraper is a piece of heavy equipment used for earthmoving.The rear part has a vertically moveable hopper with a sharp horizontal front edge. The hopper can be hydraulically lowered and raised. When the hopper is lowered, the front edge cuts into the soil or...
made it cheaper to construct a high fill directly instead of first constructing a trestle from which to dump the fill. Timber trestles remain common in some applications, most notably for bridge approaches crossing floodways, where earth fill would dangerously obstruct floodwater.
Timber trestles
One of the longest trestle spans created was for railroad traffic crossing the Great Salt LakeGreat Salt Lake
The Great Salt Lake, located in the northern part of the U.S. state of Utah, is the largest salt water lake in the western hemisphere, the fourth-largest terminal lake in the world. In an average year the lake covers an area of around , but the lake's size fluctuates substantially due to its...
on the Lucin Cutoff
Lucin Cutoff
The Lucin Cutoff is a railroad line which included a railroad trestle which crossed the Great Salt Lake in Utah. Built by the Southern Pacific Company between February 1902 and March 1904 across Promontory Point, it bypassed the original Central Pacific Railroad route through Promontory Summit...
in Utah
Utah
Utah is a state in the Western United States. It was the 45th state to join the Union, on January 4, 1896. Approximately 80% of Utah's 2,763,885 people live along the Wasatch Front, centering on Salt Lake City. This leaves vast expanses of the state nearly uninhabited, making the population the...
. It was replaced by a fill causeway
Causeway
In modern usage, a causeway is a road or railway elevated, usually across a broad body of water or wetland.- Etymology :When first used, the word appeared in a form such as “causey way” making clear its derivation from the earlier form “causey”. This word seems to have come from the same source by...
in the 1960s, and is now being salvaged for its timber.
Many wooden roller coaster
Roller coaster
The roller coaster is a popular amusement ride developed for amusement parks and modern theme parks. LaMarcus Adna Thompson patented the first coasters on January 20, 1885...
s are built using design details similar to trestle bridges because it is so easy to make the roller coaster very high. Since loads are well distributed through large portions of the structure it is also resilient to the stresses imposed. The structure also naturally leads to a certain redundancy (provided that economic considerations are not overly dominant). Such wooden coasters, while limited in their path (not supporting loops), possess a certain ride character (owing to structural response) that is appreciated by fans of the type.
The Camas Prairie Railroad
Camas Prairie Railroad
Camas Prairie Railroad Company was a short line railroad in northern Idaho jointly owned and operated by Northern Pacific Railway and Union Pacific Railroad. The Camas Prairie Railroad was known as the "railroad on stilts" due to the many wooden trestles. In one five mile stretch, there were...
in northern
North Central Idaho
North Central Idaho is an area which spans the central part of the state of Idaho and borders Oregon, Montana, and Washington. It is the southern half of the Idaho Panhandle region and is rich in agriculture and natural resources. Lewis and Clark travelled throughout this area on their journey to...
Idaho
Idaho
Idaho is a state in the Rocky Mountain area of the United States. The state's largest city and capital is Boise. Residents are called "Idahoans". Idaho was admitted to the Union on July 3, 1890, as the 43rd state....
utilized many timber trestles across the rolling Camas Prairie. The major trestle across Lawyers Canyon was the exception, constructed of steel.
In the United Kingdom
In the United KingdomUnited Kingdom
The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...
, timber trestles were relatively short-lived as a structural type, one of their major uses being to cross the many deep valleys in Cornwall
Cornwall Railway viaducts
The large number of Cornwall Railway viaducts were necessitated by the topography of Cornwall, United Kingdom, where hills and areas of high ground are separated by deep river valleys that generally run north or south...
on the spinal rail route through that county. These were all replaced by masonry viaducts.
So few timber trestles survived into the 20th century. Two that did, and which are still in daily use, cross the Afon Mawddach on the coast of Wales
Wales
Wales is a country that is part of the United Kingdom and the island of Great Britain, bordered by England to its east and the Atlantic Ocean and Irish Sea to its west. It has a population of three million, and a total area of 20,779 km²...
only a few miles apart, at Barmouth
Barmouth Bridge
The Barmouth Bridge is a single-track largely wooden railway viaduct that crosses the estuary of the Afon Mawddach river on the coast of Cardigan Bay between Morfa Mawddach and Barmouth in Gwynedd, Wales...
and Penmaenpool
Penmaenpool
Penmaenpool is a village on the south side of River Mawddach in Wales, near Dolgellau.- Points of interest :*Penmaenpool toll bridge - wooden tollbridge built in 1879, Cadw registered building...
. The former, built in 1867, carries trains on the heavy rail Cambrian Coast Line travelling from England via Shrewsbury to the various small towns on Cardigan Bay
Cardigan Bay
Cardigan Bay is a large inlet of the Irish Sea, indenting the west coast of Wales between Bardsey Island, Gwynedd in the north, and Strumble Head, Pembrokeshire at its southern end. It is the largest bay in Wales....
. It also carries a toll-path for pedestrians. Road traffic at this location has to travel many miles around the estuary to cross at either (for light traffic) the second trestle bridge, at Penmaenpool, which is a toll bridge; or (for heavy traffic) at Dolgellau
Dolgellau
Dolgellau is a market town in Gwynedd, north-west Wales, lying on the River Wnion, a tributary of the River Mawddach. It was the county town of the former county of Merionethshire .-History and economy:...
even further up the estuary.
Iron Trestles
Trestles in cast- or wrought-iron were used during the 19th Century on the developing railway network in the United KingdomUnited Kingdom
The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...
. These generally carried decking consisting of some form of trussed girder, as at Crumlin Viaduct, Belah, and Meldon; though two rare examples, at Dowery Dell
Dowery Dell
Dowery Dell, near Hunnington in Worcestershire, was notable for a cast iron railway viaduct that carried the Halesowen to Longbridge railway until it was dismantled in 1964....
(demolished in 1962), and Bennerley
Bennerley Viaduct
Bennerley Viaduct is a disused railway viaduct spanning the Erewash Valley between Awsworth in Nottinghamshire and Ilkeston in Derbyshire.- Origins :...
had lattice girder
Lattice girder
A lattice girder is a girder where the flanges are connected by a lattice web. This type of design has been supplanted in modern construction with welded or bolted plate girders, which use more material but have lower fabrication and maintenance costs...
decks.
Steel trestles
The steel trestle shown below is a modern structure with a long expected lifetime compared to a wooden trestle. Being fire resistant in this brushy location is also an advantage. The approaches to the Kate Shelley High BridgeKate Shelley High Bridge
The Kate Shelley High Bridge is among the highest double-track railroad bridges in the United States. It is located approximately 3 miles west of the city of Boone, Iowa....
are steel trestles.
New Orleans utilizes steel
Steel
Steel is an alloy that consists mostly of iron and has a carbon content between 0.2% and 2.1% by weight, depending on the grade. Carbon is the most common alloying material for iron, but various other alloying elements are used, such as manganese, chromium, vanadium, and tungsten...
trestles to support parts of I-10
Interstate 10 in Louisiana
Interstate 10, a major transcontinental Interstate Highway in the Southern U.S., runs across the southern part of the U.S. state of Louisiana. It passes through Lake Charles, Lafayette and Baton Rouge before dipping south of Lake Pontchartrain to serve the New Orleans area and then passing through...
, the Pontchartrain Expressway
Pontchartrain Expressway
The Pontchartrain Expressway is a parallel 6-lane section of Interstate 10 and U.S. Route 90 in New Orleans, Louisiana. The designation begins on I-10 near the Orleans Parish/Jefferson Parish line at the I-610 Split. The expressway follows I-10 into the Central Business District of New Orleans ...
, and Tulane Avenue
Airline Highway
Airline Highway is a divided highway in the U.S. state of Louisiana, built in the 1930s and 1940s to bypass the older Jefferson Highway. It carries U.S. Highway 61 from New Orleans northwest to Baton Rouge, and U.S. Highway 190 from Baton Rouge west over the Mississippi River on the Huey P. Long...
. Also, trestles support the elevated railroad leading to and from the Huey P. Long Bridge.