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9.6 Integral FE Bridge Deck with Soil and Hydrostatic Pressure Loads

Permissions Recommend to library. Related search. By Author M. No search history Recently Viewed. Loads and load distribution. Gerard Parke and Nigel Hewson.

SA35: Influence Line and Moving Load Series in Trusses

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. 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. 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 Pennsylvania , continued to build steel truss bridges, including massive steel through-truss bridges for long spans.

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Other states, such as Michigan , used standard plan concrete girder and beam bridges, and only a limited number of truss bridges were built. 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 an example of this was the IW Mississippi River bridge. When the truss members are both above and below the roadbed it is called a through truss an example of this application is the Pulaski Skyway , 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 road traffic. Since through truss bridges have supports located over the bridge deck, they are susceptible to being hit by overheight loads when used on highways — the I-5 Skagit River Bridge collapsed after such a strike, and such impacts were common and required frequent repairs before the collapse.

The through truss Skagit River Bridge on Interstate 5 collapsed after an overhead support was hit by a passing truck.

It carries three lanes of automobile traffic on top and two of rail below over nine truss spans. The Hart Bridge spanning the St.

Bridge Structure - an overview | ScienceDirect Topics

A railway bridge with a rail track in Leflore County, Mississippi. Bridges are the most widely known examples of truss use. There are many types, some of them dating back hundreds of years. Below are some of the more common designs. The Allan truss , designed by Percy Allan , is partly based on the Howe truss. Also constructed of ironbark, the bridge is still in use today for pedestrian and light traffic.

The prefabricated and standardized truss elements may be easily combined in various configurations to adapt to the needs at the site. In the image, note the use of doubled prefabrications to adapt to the span and load requirements. In other applications the trusses may be stacked vertically. The Baltimore truss is a subclass of the Pratt truss.

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A Baltimore truss has additional bracing in the lower section of the truss to prevent buckling in the compression members and to control deflection. It is mainly used for rail bridges, showing off a simple and very strong design. In the Pratt truss the intersection of the verticals and the lower horizontal tension members are used to anchor the supports for the short-span girders under the tracks among other things.

With the Baltimore truss, there are almost twice as many points for this to happen because the short verticals will also be used to anchor the supports. Thus the short-span girders can be made lighter because their span is shorter. The Bollman Truss Railroad Bridge at Savage, Maryland , is the only surviving example of a revolutionary design in the history of American bridge engineering.

The type was named for its inventor, Wendel Bollman , a self-educated Baltimore engineer. It was the first successful all-metal bridge design patented in to be adopted and consistently used on a railroad. The design employs wrought iron tension members and cast iron compression members. The use of multiple independent tension elements reduces the likelihood of catastrophic failure. The structure was also easy to assemble. The Wells Creek Bollman Bridge is the only other bridge designed by Wendel Bollman still in existence, but it is a Warren truss configuration.

The bowstring truss bridge was patented in [10] by Squire Whipple. In the Brown truss all vertical elements are under tension, with exception of the end posts. This type of truss is particularly suited for timber structures that use iron rods as tension members. Most trusses have the lower chord under tension and the upper chord under compression. In a cantilever truss the situation is reversed, at least over a portion of the span.

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  • The typical cantilever truss bridge is a "balanced cantilever", which enables the construction to proceed outward from a central vertical spar in each direction. Usually these are built in pairs until the outer sections may be anchored to footings. A central gap, if present, can then be filled by lifting a conventional truss into place or by building it in place using a "traveling support".

    In another method of construction, one outboard half of each balanced truss is built upon temporary falsework. When the outboard halves are completed and anchored the inboard halves may then be constructed and the center section completed as described above. The Fink truss was designed by Albert Fink of Germany in the s. This type of bridge was popular with the Baltimore and Ohio Railroad. The Appomattox High Bridge on the Norfolk and Western Railway included 21 Fink deck truss spans from until their replacement in The relatively rare Howe truss , patented in by Massachusetts millwright William Howe , includes vertical members and diagonals that slope up towards the center, the opposite of the Pratt truss.

    The K-truss is named after the K formed in each panel by the vertical member and two oblique members.

    One of the simplest truss styles to implement, the king post consists of two angled supports leaning into a common vertical support. This type of bridge uses a substantial number of lightweight elements, easing the task of construction. Truss elements are usually of wood, iron, or steel. A lenticular truss bridge includes a lens-shape truss, with trusses between an upper arch that curves up and then down to end points, and a lower arch that curves down and then up to meet at the same end points.

    Where the arches extend above and below the roadbed, it is a lenticular pony truss bridge. One type of lenticular truss consists of arcuate upper compression chords and lower eyebar chain tension links. As the horizontal tension and compression forces are balanced these horizontal forces are not transferred to the supporting pylons as is the case with most arch types.

    This in turn enables the truss to be fabricated on the ground and then to be raised by jacking as supporting masonry pylons are constructed. This truss has been used in the construction of a stadium, [13] with the upper chords of parallel trusses supporting a roof that may be rolled back. An example of a lenticular pony truss bridge that uses regular spans of iron is the Turn-of-River Bridge designed and manufactured by the Berlin Iron Bridge Co.

    The Long truss was designed by Stephen H.

    Lecture 15B.2: Actions on Bridges

    Long in Usually, it happens if the biggest load is over that support and as many a possible of the remaining loads are still on the span. In determining the largest moment and shear, it is sometimes necessary to check the condition when the bigger loads are on the span and the rest of the smaller loads are outside. Skip to main content. Moving Loads. Subscribe to MATHalino. Please join our community.