Bridges must be able to withstand several types of forces. The two most common to model bridges are compression and tension, pushing and pulling respectively. The other two are torsion (twisting) and shear. Learn what these forces mean so that you can build a better model bridge.
Compression is a pushing (compressing) force. The shorter a piece of wood is, the more compression it can hold. The longer a piece of wood is, the less compression it can hold. When you compress a long stick of wood you will notice that it starts to bend. When a piece of wood breaks because of compression, we say it failed from buckling. Typically the top chord of a bridge, including model bridges, will be in compression. Different truss designs spread out the force so that various internal parts will be in compression as well.
Tension is a pulling force. Wood has the ability to resist a lot of tension. It would be hard to break a popsicle stick if you held both ends and pulled apart. Tension may be applied parallel to the grain of the wood, but should be avoided perpendicular to the grain. Wood is very strong in tension parallel to the grain, but much weaker in tension perpendicular to the grain. Also, unlike in compression, the ability of wood to resist tension does not change with its length. A shorter piece of wood should hold the same amount of tension as a longer piece.
Torsion is a twisting force. When you wring out a cloth, you are applying torsion to the cloth. If you take a stick pretzel, twist one end, and hold the other end still, it will break very easily. If you do that with a baseball bat, it will not break. However, if you take a piece of licorice and apply torsion to it, the licorice will twist around several times before it breaks. Each of these materials has a different way of responding to torsion. Bridge designers must watch for torsion and try to reduce it as much as possible.
Shear is an interesting force. It happens when there are two opposing forces acting on the same point. If you hold a piece of wood with both hands next to each other, and push up with one hand and down with the other, you are applying shear to that piece of wood. Shear usually occurs horizontally, and not vertically.
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Physics-Bridge Project Essay
2226 WordsOct 30th, 20129 Pages
Humans have tamed steel, stone, lumber, and even living vegetation, all in effort to reach the people, places, and things that we desire. Although the concept of bridges is as simple as a tree falling across a creek, bridge design and construction requires very serious ingenuity. Artists, engineers, and architects pour vast resources into bridge construction so that they can reshape our daily environment for the better. When building bridges you’ll need help from BATS which are the key structural components of bridge construction such as beams, arches , trusses, and suspensions. Various combinations of these four technologies make it possible for numerous bridge designs, ranging from some bridges as simple as beam bridges, arch bridges,…show more content…
The truss design, which is 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. After being used for 2000 years of architectural use, the arch continues to feature prominently in bridge designs. Its semicircular structure elegantly distributes compression through its entire form and diverts weight onto its two abutments, which are the components of the bridge that directly take on the pressure being exerted onto the bridge. The tensional forces in arch bridges are virtually negligible. That is because the natural curve of the arch and its ability to dissipate the force outward greatly reduces the effects of tension on the underside of the arch. The greater the degree of curvature, the greater the effects of tension on the underside of the bridge. If you build a big enough arch, the tension will eventually overtake the support of the bridges natural structure. While there is a fair amount in variety in arch bridge construction, the basic structure of every arch bridge is the same. For example there is Roman, Baroque and Renaissance which are all architecturally different they all have the same basic structure. It is the individual arch itself gives its namesake bridge its strength. An arch made of stone doesn’t need a mortar. In fact the ancient Romans built arch bridges and aqueducts that are still standing today and are made