17 Dec. 2010|
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Below is information concerning the types of bridges and information about our bridge building project. In modern girder bridges, steel I-beams are used, but they are subject to twisting and are not good for bridges with any curve to them.
This modern bridge type uses box girders made not of steel plates but of concrete reinforced with steel bars. Suspension bridges involve a continuous girder hung from cables supported by towers erected on piers. Similar to a cable-stayed bridge except there is one main cable that runs between the towers with hanger cables below it. The girder and roadbed are not resting on the piers as with other bridge types, but is hanging from the hanger cables! A typical cable stayed bridge is a continuous girder with one or more towers erected above piers in the middle of the span. First, you must have drafted an accurate and well thought out plan before you can start building your bridge.
Drawing is extraordinarily well done with dimensions, title, scale, and details and it accurately depicts the actual bridge. Drawing is well done with dimensions, title, scale, and details and it accurately depicts the actual bridge. All students will be using equal amounts of materials to build a bridge in class in teams consisting of two students. During the course of the bridge construction project, students will be required to make sketches, and drawings of their ideas.
After reading the information about bridges go to: the Build a Bridge Game to find out if you understand the different purposes for different bridges. The arch transmits the load from the bridge deck to the abutments on both sides of the span and thus to the ground below. They are a very old bridge form, although, in their modern incarnation, they are widely used where very long spans are needed.
A truss bridge uses a series of triangles in some sort of superstructure to transfer the load from the deck to the piers. Here, the diagonal members all slant toward the closest bridge end, so they are subject to compressive forces. The introduction of steel wire cables in the 1830s greatly extended the potential of suspension bridges. Since the elements of a truss are subject only to tension (stretching) or compression (pushing) forces and cannot handle bending forces, truss bridges are typically best used for straight alignments. Students should also use this opportunity to research common problems associated with bridges. Many modern beam bridges are composed of beam girders (typically I-beams or box girders) supported on piers.
Short modern arch bridges may use wood or concrete, while longer arch spans are built of steel.
At both ends of the bridge, large anchors are placed (usually underground) to hold the ends of the main cables. A truss bridge can support heavy weights and span long distances, but it requires a fair amount of vertical room to accommodate the truss structure.
Patented by Caleb and Thomas Pratt in 1844, this was among the most common American bridge types for the ensuing decades and was built in both wood and metal. The main cables are stretched from anchor to anchor over the tops of the towers, passing over a saddle which allows the cable to slide as loads move on the bridge. Though only a few cables are strong enough to support the entire bridge, their flexibility makes them weak to a force we rarely consider: the wind. For longer span cable-stayed bridges, careful studies must be made to guarantee the stability of the cables and the bridge in the wind.
Once complete failure occurs or any part of the bridge touches the river, the bucket will be weighed to find the overall weight supported by the bridge. Since the strength of a beam bridge depends largely on the close spacing of piers, this bridge type is generally ill-suited to long spans. While other bridge types are supported by piers or abutments, here the girder and bridge deck hang suspended from the main cables. Since the abutments transfer both horizontal and vertical forces from the bridge deck, arch bridges can only be used where the ground or foundation is solid and stable. Due to the flexibility of the cables, long suspension bridges are prone to vibrate in high winds, much like the string of a guitar or violin. Construction of an arch bridge is difficult, since the structure is unstable until the two sides of the arch are joined.