Questions about Truss Bridges?

Question

-What loads work on bridges, and also, what loads are susceptible particularly to Truss Bridges?
- What negative forces may act on a Truss Bridge during events like earthquakes, storms, etc.?
- What materials are usually used to build Truss Type Bridges, and their advantage?
- What are the usual shapes used when building bridges, and also particularly Truss types? (are there more than just the triangle shape?)
I will give 20 points to anyone can answer all my questions, hows that.
Thank you in advance, i know, its alot, but i am researching Truss Bridges.

Answer 1

1º- Forces could be as example, the wind, the weight of cars...and they work in the truss bridges as tension (+) or compressive (-) forces.

2º- Forces tend to be prejudicial when they overall the limits (sigma of security) for what the structure is designed for , and each case is a case.

3º- steel is the most common material used in trusses. This is an yield material, i.e, it has the ability to allow relative long deformations before fracture witch is great to anticipate possible collapse of the structure.

4º- the most common truss types are the Pratt truss, Warren truss, Howe truss....depending the region. Truss is a triangular shape in the structures

Answer 2

Truss Bridge Materials

Answer 3

Assuming the other members at the joint are horizontal then all vertical forces must be supported by the vertical member so yes Rules for trusses: All joints are in equilibrium Joints carry no moment Members carry no moment Members carry only tension or compression Start at the roller support you know it cannot support a horizontal load===>all support forces are vertical at that joint====> all horizontal forces are supported by the pin====> neither the pin nor the roller support a moment===> that should be enough to find the reactions at both ends. Now start working through the joints from the end(s) where the joint is statically determinate and work through the joints. Remember that the compression or tension in any member is the same on both ends so when you solve a member you know the force from that member on the next joint If the joint includes 1 or more members at an angle, then the angle members MAY carry some of the vertical load. So, perhaps no.

Answer 4

I've been surfing more than 4 hours today looking for answers to the same question, and I haven't found a more interesting discussion like this. It's pretty worth enough for me.

Answer 5

I was here on Yahoo for something or other, then this question was displayed on the sidebar...

Answer 6

See the following:

http://www.du.edu/~jcalvert/tech/machines/bridges.htm

Answer 7

A truss bridge is a bridge composed of connected elements (typically straight) which may be stressed from tension, compression, or sometimes both in response to dynamic loads. Truss bridges are one of the oldest types of modern bridges. This type of bridge structure has a fairly simple design and is particularly cheap to construct owing to its efficient use of materials. For purposes of analysis most truss bridges may be considered to be pin jointed where the straight components meet. A more complex analysis may be required where rigid joints impose significant bending loads upon the elements.

The truss may carry its roadbed on top, in the middle, or at the bottom of the truss. Bridges with the roadbed at the top or the bottom are the most common as this allows both the top and bottom to be stiffened, forming a box truss. When the roadbed is atop the truss it is called a deck truss, when at the bottom of a box truss a through truss, and where the sides extend above the roadbed but are not connected, a pony truss or half-through truss.

Sometimes both the upper and lower chords support roadbeds, forming a double-decked truss. This can be used to separate rail from road traffic or to separate the two directions of automobile traffic and so avoiding the likelihood of head-on collisions.

Early truss bridges would typically use carefully fitted timbers for members taking compression and iron rods for tension members, usually constructed as a covered bridge to protect the structure. In 1820 a simple form of truss, Town's lattice truss was patented, and had the advantage of not requiring high labor skills nor much metal.
A few iron truss bridges were built in the United States before 1850. Bridges based on the Bollman truss (patented in 1852) were used successfully by the Baltimore and Ohio Railroad. Truss bridges became a common type of bridge to see built from the 1870s through the 1930s. Examples of these bridges still remain across the United States, but their numbers are dropping rapidly, as they are demolished and replaced with new structures. Wrought iron bridges in the U.S. started being built on a large scale in the 1870s. Bowstring truss bridges were a common truss design seen during this time, with their arched top chords. Companies like the Wrought Iron Bridge Company of Canton, Ohio and the King Bridge Company of Cleveland, Ohio became well-known companies, as they marketed their designs to different cities and townships. The bowstring truss design fell out of favor due to a lack of durability, and gave way to the Pratt truss design, which was stronger. Again, the bridge companies marketed their designs, with the Wrought Iron Bridge Company in the lead. As the 1880s and 1890s progressed, steel began to replace wrought iron as the preferred material. Other truss designs were used during this time, including the camel-back. By the 1910s, many states developed standard plan truss bridges, including steel Warren pony truss bridges. As the 1920s and 1930s progressed, some states, like Pennsylvania continued to build steel truss bridges, including massive steel through truss bridges for long spans. Other states, like Michigan, utilized standard plan concrete girder and beam bridges, and only a limited number of truss bridges were built.

Bridge Basics - A Spotter's Guide to Bridge Design - from Pghbridges.com - Illustrates many of the various types of truss arrangements used in bridges.
Historic Bridges of Michigan and Elsewhere - Many photos of truss bridges are available on this informative and mainly truss-focused bridge website.
Historic Bridges of the Midwest - An enormous database of historic bridges. Over 1000 truss bridges are listed here.
Iron and Early Steel Bridges of Ohio - A comprehensive inventory of all remaining truss bridges in Ohio. Includes maps, photos, and invites visitor assistance in identifying extant or demolished bridges.
Matsuo Bridge Company: Bridge Types - Truss
structurae.de The Structurae database on bridges.

Trusses are used to stiffen and support a bridge by distributing the loads and forces acting upon the bridge based on the positions of the vertical, horizontal and diagonal chords. They are based on triangular configurations. How those chords are arranged identifies the type of truss. Trusses are also used on cantilever bridges and to support the decks in suspension bridges. Trusses are "through trusses" when the truss is above the deck, and "deck trusses" when they are underneath, supporting the truss. Three early American bridgebuilders--Timothy Palmer (1751-1821), Lewis Wernwag (1770-1843) and Theodore Burr (1771-1822) built truss bridges and are known as the "Inspired Carpenters." Palmer is credited among the first to cover the the truss, leading to construction of covered bridges in the United States. The truss bridge was described as long ago as the sixteenth century by Andrea Palladio in his Four Books on Architecture.

The Betsy Ross Bridge, across the Delaware River between Philadelphia, Pennsylvania and Pennsauken, New Jersey, is relatively recent, constructed between 1969 and 1976. According to the Delaware River Port Authority, this bridge is "the first U.S. bridge named after a woman." Over 29000 tons of structural steel were used for the bridge and its approaches. It is a continuous through truss bridge. Its length, from abutment to abutment, is given at 8,485 feet. The main span is 729 feet long, and the two side spans are 364½ feet each. The equilateral triangles are typical of the Warren Truss design, which is common for simple and continuous truss bridges.

The Warren Truss was patented in 1848 by James Warren and Theobald Manzani and is marked by equilateral triangles. David W. Harris, in his book Truss Fun, notes that "the diagonals carry both compression and tension forces," and "Warren Trusses generally can span distances of 50 to 400 feet." Variations include the subdivided Warren Truss, with vertical members bisecting the triangles, (as in the Uhlerstown-Frenchtown Bridge below), the double warren (shown below in the Washington Crossing Bridge and Riverton_Belvidere Bridge) evidencing a diamond-like appearance, and the quadrilateral Warren Truss

The Pratt Truss was invented in 1844 by Thomas and Caleb Pratt. In this configuration, the diagonals are in tension and the verticals in compression. The diagonals slant downward and towards the center. This truss can be used with spans up to 250 feet and was a common configuration for railroad bridges as truss bridges moved from wood to metal.

In his article in American Heritage Magazine in 1994 titled The Golden Age of the Iron Bridge, Eric DeLony wrote that cast iron and wrought iron bridges are "the rarest and least appreciated . . . Yet in some ways [they are] the most technologically significant." Their heyday was between 1840 and 1880, after the age of wood and before the age of steel. Cast iron is an iron alloy with high carbon content that, while in common use in Roman times, first became economical at the beginning of the Industrial Revolution in the mid-18th century. Wrought iron has lower carbon content and is more flexible.

Hope this helps, and good luck in your research.