Introduction
An inspiring old English proverb states "let every man praise a bridge". In everyday use bridges are taken for granted, we expect them to make our paths of travel easy and efficient. Since early civilizations, bridges have played a significant role in linking communities and cultures.
Bridges affect everyday life in some of the most unique ways. The unique way that they affect us can be through environment, location and economics. They exist so that they can be used by us. Bridges can be created as well for aesthetic qualities. This can be for enhancement of the environment. As stated by Martin Gehner, Professor Emeritus of Architectural Engineering at Yale University, "Bridges like no other human artifact, better represents the human need for continuity, life and change." The bridge in itself makes our lives easier. For instance their, location is important in the fact that, the bridge, connects one community to another. The bridge makes crossing a river, terrain or mountain accessible to communities other wise separate. Another important factor is environment. When writing about environment several factors come into play namely weather patterns. The bridge has to with stand these conditions over a long period of time.
The climate imposes a significant effect on a bridge. The climate in my city changes seasonally, thus giving our bridges a break from one particular type of weather season over a long length of time. Another factor when bridges are built is economics. The economic condition of the place where the bridge is built is important to the community. The bridge makes traveling from one mall to another easier. The city depends on bridges to make significant connections between people within the larger region. It helps with the transportation of goods and material over rivers. Bridges make it easier for local resources to be imported and exported.
First of all a bridge is like the game tug of war where each team has equal weight. If each side is equal it will balance out. They are pulling and pushing but no side falls. That's how a bridge stays up. The bridge's members are either in compression or tension. This is the tug of war that is involved with the structure of the bridge. The members are built to keep the bridge in a balanced state. You can tell a bridge is a bridge because it has a deck, supports, a span and a foundation. These basic members comprise the whole bridge's structure. What has made the bridge of interest to me as a teacher is their total existence.
This unit will explore my hometown of Pittsburgh, Pennsylvania by looking at several truss bridges. While looking at the truss bridges, I will be using computer interactive software games involving a tangram puzzle. In the tangram puzzle there are polygon shapes the square, triangle and parallelogram and in which the triangle is a major shape in the truss design. Trusses become efficient and strong structural systems through the use of triangular geometry of its members. The trusses that will be used in this unit are the steel trussed lattice type, the lenticular truss, and the steel arched form.
My city is in the north east and is often called the city of bridges. It has acquired this name because it has the most bridges per capita in the world. (Flying off the Bridge to Nowhere and other tales of Pittsburgh Bridges) (1993) we have hills, mountains and rivers so this topography lends to a community of bridges. Pittsburgh is unique in the fact that it has three self anchored suspension bridges; that are called sister bridges because they are right next to each other. The city is noted for great bridge companies such as American Bridge Corporation, which is currently repairing bridges across the country, and the G.W.G. Ferris and Company which inspected bridges in the 1800s. This later company was founded by George Washington Gale Ferris, Jr. George made one of the first steel bridges in America and also he invented and built the first Ferris wheel. His main focuses in both of his inventions were unique applications for tension, compression, load and capacity of structural systems. I will be looking at these concepts in the truss bridge. Andrew Carnegie an industrialist, made cast iron train bridges, Bessemer steel bridges and several museums are named after him here in Pittsburgh. The truss initially was made for the railroad, because of its capability to carry heavy loads. We will look at these pioneers in depth. Pioneers are inspiring models for creative young minds to study while exploring the four Ts. Pittsburgh and its many bridges will be a resource in researching the history of bridges.
The first T is the geometric shape Triangle. This is a polygon. This shape provides the basic stable geometry designing of a truss. Another important polygon is a square. This shape is initially used with a diagonal brace to create a stable form. This brace makes two triangles within the square and makes the weaker square into two strong triangles. In looking at the triangle I will discuss single forces that when added create an imposed load. In this instance I would like to research the math and science aspects related to bridge design related to forces.
The second T is Tangram used in combination with the third T Technology. A tangram originated in China. It involves polygons that are used in a puzzle. You make two- dimensional designs with this puzzle. The problem contains five triangles, one square and a parallelogram. This part of the unit is technology driven.
The puzzle is on software provided by the Public Broadcasting Company. It can be accessed at pbskids.org. The software provides an opportunity to design different figures and objects. Design is so important when making bridges. The bridge may become a wonderful picture as in the tangram. The tangram game will provide my students with methodical design making. This is a basic way of letting them experience some visual geometrical patterns of bridge design. They will put things together to create a bridge, and engage themselves in exploring how things fit together. In this part of the unit I will also discuss the designer/ architects Lindenthal and Ferris. Lindenthal designed the Smithfield Bridge and Ferris just happen to have invented the Ferris wheel which just happens to have triangles, and not only did he do that, he designed a bridge. Andrew Carnegie as well will be discussed because of his iron bridges for rail cars. I am including the iron bridges because of their importance with the design of the truss. The designing engineer must consider several factors when designing a bridge. They consider the distance to be crossed and the community within which it will be located. These considerations and the history of Pittsburgh will help with the development of this unit. In this section of the unit my students will do journal drawings of bridges. This will help them with the visual application of bridge making.
The Truss is the fourth T. I choose the truss bridge because of its simple design. Trusses are created by fastening structural elements together to form triangles. It has so many great scientific principles related to support, strength and capacity. The simple truss is an endangered bridge. I will use the truss to discuss bridges in general. Truss bridges have strong frames that support many other bridges such as the arch, beam and cantilever over its span. The framework distributes the load. They can carry heavy loads and are economical to build. Some of the other bridge types incorporate the truss principles.
I will look at the purpose of a bridge and why it is so important to transportation and a
community. As a cumulative activity we will be taking a field trip to all of the bridges in this unit. So in writing about the four Ts, I will be looking at mathematics, sciences, visual arts and history using variety of stories to motivate and arouse the student's interest.
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