Ryan+S

Jack Pulito and Ryan Sileno 8th hour science December 3, 2010

Kintai Bridge Project Report

We learned many things about bridges through this project. We learned about how bridges balance forces, the structure of modern bridges, the history of bridges, the three types of bridges, how physics and geometry are used to build bridges, and about the Kintai Bridge. By the 1800s in the United States, bridge builders began to use cast iron instead of stone and wood. By the late 1800s, they were using steel, which was strong and relatively lightweight. The use of new building materials was not the only change. Engineers began designing different types of bridges as well. They found that they could build longer, larger bridges by using a suspension structure. The three types of bridges are beam bridges, arch bridges, and suspension bridges. A beam bridge is a bridge built on beams. When using this bridge the compression force is inward, the tension force is pushed outward and the reaction force is pushed up the beams. An arch bridge is built on top of an arch. The compression forces are pushed from the bottom of the arch to the land while reaction forces push in the opposite direction on the arch. A suspension bridge is built on beams with suspension cables running throughout the top of the bridge in multiple “U” shapes. In this bridge tension forces are pushed from the suspension cables to the beams while reaction forces are pushed up the beam and out the sides of the bridge. Physics is a main focus on builder’s minds when building a bridge. The weight of the bridge and the traffic on it are called the load. When a heavy truck crosses a beam bridge, the weight of the load forces the beam to curve downward. This creates tension forces that stretch the bottom of the beam. At the same time, the load also creates compression forces at the top of the beam. The bridge does not collapse because there are upward forces that balance the downward forces. Other examples of physics being used in building bridges are the reaction forces that oppose one another and the cables under tension. Geometry is also used in building bridges. Engineers use various geometric figures in drawing bridge plans. Figures that have right angles are squares, rectangles, and triangles. Figures that have acute angles and obtuse angles can be triangles and parallelograms. The accuracy of the design of a bridge is crucial to handling to stress from heavy train loads and constant vibrations. As in all bridge structures, each steel piece has to be measure and fitted accurately- including widths, lengths, angles, and points of intersection and attachment. We used physics when building our bridge model. We built our arches so the compression forces push out of the bottom of the arches into the bricks while the bricks pushed a reaction force on the arches. The bridge we chose to build our model after is the Kintai Bride in Iwakuni, Japan. This bridge is an arch bridge because it is made with five arches. It was built in 1673. It has been rebuilt and restored for the past three hundred and twenty seven years. It is composed by five wooden arches on four stone columns as well as two wooden columns on the riverbed. Each of the three middle arches is each 35.1 meters long while the two end arches are each 34.8 meters long. This is a total of about 175 meters long with a width of five meters. We chose to build a model of this bridge because it looked very interesting and appealing to us. It caught our attention and we thought it would be fun to make a model of it. We learned a lot from this project. This includes the three types of bridges, how bridges have changes throughout history, how physics and geometry are used in building bridges, about the Kintai Bridge, and its history.

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