Truss bridges

The triangular units forming the truss are slim and straight in form.

Truss bridges

For purposes of analysis, trusses are assumed to be pin jointed where the straight components meet. This assumption means that members of the truss chords, verticals and diagonals will act only in tension or compression.

A more complex analysis is required where rigid joints impose significant bending loads upon the elements, as in a Vierendeel truss. In the bridge illustrated in the infobox at the top, vertical members are in tension, lower horizontal members in tension, shearand bending, outer diagonal and top members are in compression, while the Truss bridges diagonals are in tension.

The central vertical member stabilizes the upper compression member, preventing it from buckling. If the top member is sufficiently stiff then this vertical element may be eliminated.

If the lower chord a horizontal member of a truss is sufficiently resistant to bending and shear, the outer vertical elements may be eliminated, but with additional strength added to other members in compensation. The ability to distribute the forces in various ways Truss bridges led to a large variety of truss bridge types.

Some types may be more advantageous when wood is employed for compression elements while other types may be easier to erect in particular site conditions, or when the balance between labor, machinery and material costs have certain favorable proportions.

The inclusion of the elements shown is largely an engineering decision based upon economics, being a balance between the costs of raw materials, off-site fabrication, component transportation, on-site erection, the availability of machinery and the cost of labor.

In other cases the appearance of the structure may take on greater importance and so influence the design decisions beyond mere matters of economics.

Modern materials such as prestressed concrete and fabrication methods, such as automated weldingand the changing price of steel relative to that of labor have significantly influenced the design of modern bridges. Model bridges[ edit ] A pure truss can be represented as a pin-jointed structure, one where the only forces on the truss members are tension or compression, not bending.

This is used in the teaching of statics, by the building of model bridges from spaghetti. Spaghetti is brittle and although it can carry a modest tension force, it breaks easily if bent. A model spaghetti bridge thus demonstrates the use of a truss structure to produce a usefully strong complete structure from individually weak elements.

History in the United States[ edit ] Warren-type through-truss of the former Seaboard Air Line Railwaylocated near the village of Willow, Florida ; abandoned since the mids Because wood was in abundance, early truss bridges would typically use carefully fitted timbers for members taking compression and iron rods for tension membersusually constructed as a covered bridge to protect the structure.

Few iron truss bridges were built in the United States before Truss bridges became a common type of bridge built from the s through the s.

Examples of these bridges still remain across the US, but their numbers are dropping rapidly, as they are demolished and replaced with new structures.

As metal slowly started to replace timber, wrought iron bridges in the US started being built on a large scale in the s. Bowstring truss bridges were a common truss design during this time, with their arched top chords.

The bowstring truss design photo fell out of favor due to a lack of durability, and gave way to the Pratt truss design, which was stronger.

Truss bridges

Again, the bridge companies marketed their designs, with the Wrought Iron Bridge Company in the lead. As the s and s progressed, steel began to replace wrought iron as the preferred material. Other truss designs were used during this time, including the camel-back.

Basics of Truss Bridges

By the s, many states developed standard plan truss bridges, including steel Warren pony truss bridges. As the s and s progressed, some states, such as Pennsylvaniacontinued to build steel truss bridges, including massive steel through-truss bridges for long spans.When people reflect on "historic bridges," they most often envision covered wooden truss bridges.

With its picturesque design, the wooden truss bridge has a near universal appeal. For many years, travelogues and historians alike have documented them and promoted their preservation, more than any. Excel Bridge bridge engineers build any types of bridges your project requires, from truss bridges, arch bridges, beam bridges, steel bridges and more.

Call now. Truss bridge is a type of bridge whose main element is a truss which is a structure of connected elements that form triangular units. Truss is used because it is a very rigid structure and it transfers the load from a single point to a much wider area.

Truss bridges appeared very early in the history of modern bridges and are economic to construct because they use materials efficiently.

Truss Bridge Construction

All these different truss patterns also factored into how beam bridges were being built. Some takes featured a through truss above the bridge, while others boasted a deck truss beneath the bridge..

A single beam spanning any distance undergoes compression and tension. Truss is a formation produced by triangular components, in accordance with the truss bridge drawings, and coupled at joints known as nodes. The truss bridge construction is initiated with a detailed soil analysis to determine the suitability of soil for the bridge and traffic loads.

List ranked by length of main span. The length of main span is the most common method of comparing the size of bridges. The length of the main span will often correlate with the depth of the truss (height the truss from bottom to top) and the engineering complexity involved in designing and constructing the bridge.

Truss Bridge - Facts and Types of Truss Bridges