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Bridges. The Big Idea. Construction is the systematic process of erecting structures to meet human needs and desires. It reflects cultural norms, environmental conditions, and the requirements of enterprises and institutions. The Infrastructure.
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The Big Idea • Construction is the systematic process of erecting structures to meet human needs and desires. It reflects cultural norms, environmental conditions, and the requirements of enterprises and institutions.
The Infrastructure Ever wonder how the electricity gets to everyone's house? Ever wonder how large cities can supply everyone with water? Ever wonder where all that waste material goes when you flush the toilet? Ever wonder how your favorite store gets their products? It is the infrastructure. The underlying base or basic framework of our nation.
What about Bridges? • Everyone has seen a bridge, and it’s almost as likely that you’ve traveled over one today. • Maybe you laid a plank or log over a stream to keep from getting wet, you’ve even constructed a bridge. • Bridges are an important part of our nations infrastructure. • A bridge provides passage over some sort of obstacle: a river, a valley, a road, railroad tracks, etc. • Think about the longest and highest bridge you have ever crossed.
Bridges • There are three major types of bridges (beam bridges, arch bridges, and suspension bridges). • The biggest difference between the three is the distances they can cross in a single span. • A span is the distance between two bridge supports, whether they are columns, towers, or the wall of a canyon. • A modern beam bridge, for instance, is likely to span a distance of up to 200 feet while a modern arch can safely span up to 800 or 1,000 ft • A suspension bridge, the pinnacle of bridge technology, is capable of spanning up to 7,000 ft
Suspension Bridges • This basic suspension bridge design can be applied using other materials to build larger, stronger bridges.
Suspension Bridges • A suspension bridge’s cables and towers transmit the dead load of the bridge deck and the live load of traffic to the massive anchor blocks at each end of the bridge. • The tension in the cables leading up from the bridge deck is balanced by the tension in the cables leading to the anchor blocks, as well as the compression in the towers. • The anchor blocks must be massive enough to resist the tension in the cables caused by the weight of the bridge deck.
Arch Bridge • An abutment is the part of a structure that • bears the weight of an arch, • supports the end of a bridge, • anchors the cables of a suspension bridge.
Beam Bridges • A single beam spanning any distance experiences compression and tension. • The very top of the beam experiences the most compression, and the very bottom of the beam experiences the most tension. • The middle of the beam experiences very little compression or tension.
Beam Bridges • A truss system takes this concept one step further. Think of one side of a truss bridge as a single beam. The center of the beam is made up of the diagonal members of the truss, while the top and bottom of the truss represent the top and bottom of the beam. • Looking at a truss in this way, we can see that the top and bottom of the beam contain more material than its center (corrugated cardboard is very stiff for this reason).
Beam Bridges • Another reason why a truss is more rigid than a single beam: A truss has the ability to dissipate a load through the truss work. • The design of a truss, which is usually a variant of a triangle, creates both a very rigid structure and one that transfers the load from a single point to a considerably wider area.
