![]() Therefore, most beam bridges rarely span more than 200 feet (61m), however, old truss bridges crossing major rivers are often as long as 500-600 feet (152-183m), not including end supports such as piers.Īrch bridges are the easiest type of bridge to recognize. Engineers have used many different truss patterns in bridges. For larger beam bridges designed for heavy car and railroad traffic, the beams are substituted by simple trusses, or triangular units, which are more economical than solid beams. The farther apart the supports or piers, the weaker a beam bridge becomes. When a load pushes down on the beam, the top portion of the beam is pushed together by a compressive force while a tensile force stretches the lower portion. However, the beam itself must be able to support its own weight and loads between the piers. The weight of the beam and any additional load on the bridge is transferred directly to the piers. ![]() The most simple beam bridges consist of a horizontal beam that is supported on each end by columns or piers. Used with permissionīeam bridges are the simplest and least expensive type of bridge to build. It is the purpose of the bridge design to handle these forces without breaking or failing in some manner.Ĭopyright © 2007 Denise W. Thus, a force of tension is acting on it to lengthen the spring. If we pull both ends of the spring away from each other, we are stretching the spring. Thus, a force of compression is acting on it to shorten the spring. If we push both ends of the spring towards each other, we are compressing the spring. Tension, or tensile force, is a force that acts to expand or lengthen the thing it is acting on. Compression, or compressive force, is a force that acts to compress or shorten the thing it is acting on. Two major forces act on a bridge at any given time: compression and tension. To understand how bridges work, we must understand the forces that act on every bridge. Three basic types of bridges used in transportation are: beam and truss bridges, arch bridges and suspension bridges. (Show a map of Vancouver, BC, Canada, or another city with many bridges.) For example, the jutting features of Vancouver would be difficult to access if it were not for the bridges that tie this region together. Think about bridges as a way that engineers help us bring worlds together. Who designs these bridges? Civil engineers do. Bridges enable roadways to pass through varying terrain, over waterways and through mountains with minimal deviation, saving time in transport or commute or even connecting areas that would otherwise be inaccessible. What impacts do bridges have on our communities and cities? Bridges provide essential links between places, providing us with access to resources, other places and other people. (Optional: Provide each student with a copy of the Bridge Notes Worksheet to fill-in what they know about bridges before the activity and take notes on during the introduction portion of the activity.) Explain situations for which different types of bridges would be best suited. ![]() Describe and locate compressive and tensile forces acting on various types of bridges.Define three major types of bridges, including a beam or truss bridge, an arch bridge, and a suspension bridge.Teams of engineers decide on the bridge type, design and materials to best distribute the load across an obstacle, and draw detailed design plans, specifying materials, measurements, shapes and angles for construction of the bridge.Īfter this activity, students should be able to: To design bridges of any type, engineers must understand the forces that act on every bridge: compression and tension, and then design bridges to handle these forces without breaking or failing. Using the countless design possibilities of beam, truss, arch and suspension bridges, civil and structural engineers create the bridges that are essential to the infrastructure of our world. Students model different bridge types such as a cable-stay bridge
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