CONTEXT:

The need to move from one point to another has existed from prehistoric times to the present day.  Often the path is free of obstacles, but at one time or another, insects, land animals, and human beings must bridge a gap or overcome a natural barrier in order to complete a journey from Point A to Point B.

Whether it was a small river or a massive river gorge, structures had to be built to provide safe passage for travelers and their cargoes of food, tools, clothing and other necessities.  Wood, stone, brick, and later metal proved to be reliable construction materials. As technology advanced, these materials were used in combination to bridge greater distances and to support heavier loads.

Early bridges used natural materials, such as a fallen trees and rocks from a stream.  Rubble from streambeds was often used to construct Stone Arch bridges; this was a rough and unfinished stone.  Squared stone, shaped into rectangular pieces, and ashlar (a further refinement of the stone) improved upon the appearance and longevity of timber bridges.  Today's state-of-the-art suspension bridges use advanced engineering designs and materials, including wire cables and reinforced concrete to distribute the load or weight of the bridge and its load.

As America entered the Industrial Revolution, metal truss bridges became the standard for construction. Moveable bridges in floating, swinging, and drawbridge styles offered features beyond the inherent strength of steel. By surrounding steel I-beams and reinforcement bars with concrete, bridges could span greater distances while using fewer materials (which meant less bridge weight). These bridges were able to carry much heavier loads, even supporting two decks for vehicles moving in opposite directions.  As modern highways developed around the world, new designs, materials, and construction methods have allowed bridges to reach higher and farther than ever imagined.

CHALLENGE:

EXPLORATORY
Research and report upon a bridging structure. Compare and contrast your selected design with another student or group.
 
INTERMEDIATE
Using a single design for a bridging structure, construct similar models using an least three (3) different materials (paper, wood, foil, plastic, etc.). Test each model and compare the strengths and weaknesses of the different materials used.
 
ADVANCED
Design and construct a structure with the provided materials that will have a clear span of 75 cm between supports and meet a chosen standard for strength, flexibility, and weight. 

MATERIALS:

EXPLORATORY

• Texts, references, and other readings, or Internet if available
• Student bridges from previous years for contrasting and comparison

INTERMEDIATE

• Cardboard
• Paper, various weights/colors
• Aluminum foil
• Plastic pieces
• Other found materials
• Glue, masking tape. scissors. X-acto knife
• Bridge Tester or;
• Bridge Tester or free weights, clay, sand bags, etc.

ADVANCED

• Wooden toothpicks (boxes of 750)
• Guitar strings (wire)
• Bridge Tester or free weights, clay, sand bags, etc.
• Slabs of foam (sections cut  from old foam cushions)

CRITERIA:

Your success on this Challenge will be based on your completion of the activities below. Three general criteria for your performance will be: your participation in the activity; the accuracy of your measurement and model construction; and the performance of your design.  Your teacher will help you understand how your performance will be graded.

EXPLORATORY

• Research and report upon a bridging structure. View past student work, if available.
• Write several paragraphs that summarize the bridge?s structural elements.
• Work with another group or individual student; compare and contrast your designs.
• Write a brief summary of your findings.
• Present your design.

INTERMEDIATE

• Research a bridging structure. View past student work, if available.
• Research basic construction techniques (corrugation, beam, truss, etc.)
• Choose one construction technique; find an example of a bridge built with that technique.  Write a list of the materials needed to build a model of that bridge.
• Build the model using only the materials approved for the project.
• Devise a strength test; test the model; present your design and the test results.
• Compare the strength of the different materials used.

ADVANCED

• Research a bridging structure. View past student work as well.
• Research basic construction techniques (corrugation, beam, truss, etc.)
• Sketch and/or draw a design, to scale that includes a clear span of 75 cm between supports.
• Based on your design, determine what materials are needed and gather those materials
• Build the model with the approved materials.  Determine the weight of the finished model.
• Devise a strength and flexibility test; test the model; present your design and the test results.
• Compare and contrast the different materials and construction techniques.  The "best" design may be one that is strongest and most flexible, but with the lowest total weight