Pre-Stressed and Post-Tentioned Concrete Bridges

Grade Level: 
High School
Technology Education, STEM
Lesson Overview:
To develop skills with bridges, modern bridge design, pre-stressed and post-tensioned concrete beam bridges, teams of two students will design and construct a reinforced concrete bridge model from cement, sand, and copper wire to withstand the largest load while minimizing the bridge costs.
Design constraints:
  • Bridge must use a reinforced concrete design.
  • Models will be constructed using a mixture of cement, sand, and 28 Gage copper wire.
  • Length of span is 12”.
  • Height will be less than 1 ½”.
  • Distance between sides will be greater that 5” and less than 6”.
  • The road deck will be continuous without holes or gaps.
  • A load plate 2” X 2” will be used to load the structure at the mid span point.
  • There must be a 3/8” hole through the roadway deck at the mid span point to allow for the load piston to enter and connect to the load plate.
  1. Analyze different bridge designs and uses.
  2. Analyze modern highway bridges strengths/weaknesses.
  3. Analyze material properties of cement, sand, and wire. Calculate proper material usage and ratios for best outcome.
  4. Define and label parts of modern bridges.
  5. Understand, draw, and calculate bridge load paths using free body diagrams.
  6. Define and apply concepts of reinforced concrete construction, including pre-stressed and post-tensioned in the building of bridge model.
  7. Complete bridge model and design book (which includes bridge drawing, daily journal, pictures, calculations, definitions, etc.).
Time Required: 

Projected Timeline: 2 Weeks (based on block 90min every other day)



Week 1
Day 1
         Introduction to bridges/Review Material Categories & Properties
         Assign Chapters 1-2 Design of Highway Bridges/Discuss
         Introduce Bridge Building Activity
         Check students initial sketches
Day 2
         Begin final design drawing on Inventor/
Quiz on Chapters 1-2 Design of Highway Bridges
         Start Building Bridges
         Collect Software design Drawing
Week 2
Day 1
         Continue Bridge Construction
Day 2
Load Test Bridges
Day 3
         Student Presentations
         Collect Student Design Books
         Follow-Up Activity
Materials Needed:
  • Cement
  • Fine Sand
  • Copper wire
  • Scrap Wood
  • Sheet Metal/Aluminum Foil
  • Graph Paper
  • Computer with design software
  • Tensile Tester
Skills/knowledge gained by learners:
  1. Identifies talents/skills within team and delegate responsibilities. Allocate set dollar amounts to each material. Develop timelines for project completion.
  2. Brainstorm bridge ideas. Identify roles and tasks. Teams will give oral presentation to class in which they will instruct students on what was successful for them in the bridge design and building.
  3. Teams will evaluate the different materials available for bridge construction. They will analyze the results of their bridge model using free body diagrams before constructing a bridge.   Teams will organize collected data into their design book.
  4. Teams will monitor changes in bridge performance with change in copper wire or concrete. They will develop alternate bridge plans.
  5. Teams will use a variety of technology including computers (Word, PowerPoint, Inventor 8.0, & Publisher), calculator, scale, band saw, table saw, belt sander, drill press, box and pan brake, various hand tools, tensile tester.
  • Create a computer drawing of the bridge-using design software. Submit an isometric and oblique drawing (side, plan, and front).
  • Use a plot of the drawing as a template for constructing the false-works (forms) of the bridge to be poured with concrete.
  • Create a design book, which will include initial sketches, final drawings, and daily entries.
  • Load test bridge to failure.
  • Calculate bridge efficiency.
  • Present bridge outcomes to class in 5-minute presentation.
Closure (How to draw the project to a close):
  1. Each bridge model will be summed for total costs (1oz of cement = $100, & 1oz of copper wire = $700). (Those numbers are based on ratios of actual concrete and steel prices.) Students and teacher will record the amount and type of material at time of “purchased”. All material that is purchased by students must be counted in final bridge costs, even if all material is not used by students (minimize waste).
  2. Each bridge model will be load tested on a tensile tester to failure.
  3. Models will be ranked based on an efficiency number. The efficiency of each model will be calculated from:
Efficiency = Maximum Load (pounds)/ Total Cost (dollars)
  1. Summarize and wrap up with a discussion on why the team had the most efficiency when in comes to their bridge design.
  2. Each group will then present their final bridge projects
Chapter Questions/Quiz _______/50
Bridge Drawing _______/50
Load Test Efficiency _______/150
Journal _______/100
Presentation ______/100
Team Evaluation ________/50
Total Points Possible 500
Load Test Efficiency _______/150
Each model will be summed for total cost, and then load tested to failure. Models will be ranked based on an efficiency number (Load/Cost). Your score out of 150 will be determined by how efficient your bridge is. The group with the most efficient will receive 150 points. Each subsequent team in order of efficiency will receive 5 less points.
Project Journal ________/100
Your team will be required to maintain a daily journal of the bridge design and construction. At the end of the project this will be submitted as part of the project grade. The journal will be made up of the following sections:
·       Cover
·       Initial sketches
You will conceptualize your design and prepare a quality sketch of your bridge. This will be the concept you develop to completion. Any changes to your bridge will have to be sketched and documented.
·       Daily Entries
Every day keep track of your progress. Your entries must be made in the following form.
-       Date:
Tasks Accomplished
Tasks yet to be addressed
Presentation ______/100
     Power Point slides to include an Introduction slide, a slide of your free body diagrams, a picture of your bridge (before and after destruction), a slide of your initial drawing, a problems and solutions slide, & a summary slide. A time requirement of 5-10 minutes must be met.
Team Evaluation ________/50
National Standards Alignment
The National Academy of Sciences Standards:
           1.0 Science Inquiry
1.1  Ability necessary to do scientific inquiry
1.2  Understandings about scientific inquiry
2.0 Physical Science
          2.2 Structure and properties of matter
          2.4 Motions and forces
4.0 Science and Technology
          4.1 Abilities of technological design
5.0 Science in Personal and Social Perspectives
          5.6 Science and technology in local, national, and global
The National Council of Teachers of Mathematics Standards:
2.0 Patterns, Functions, and Algebra
          2.2 Use symbolic forms to represent and analyze
mathematical situations and structures
3.0 Geometry and Spatial Sense
          3.1 Analyze characteristics and properties of two- and
three-dimensional geometric objects
          3.2 Select and use different representational systems,
including coordinate geometry and graph theory
          3.4 Use visualization and spatial reasoning to solve
problems both within and outside of mathematics
4.0 Measurement
          4.1 Understand attributes, units, and systems of
          6.0 Problem Solving
                   6.1 Build new mathematical knowledge through their work
with problems
                   6.2 Develop a disposition to formulate, represent,
abstract, and generalize in situations within and
outside mathematics
                   6.4 Monitor and reflect on their mathematical thinking in
solving problems
          7.0 Reasoning and Proof
                   7.2 Make and investigate mathematical conjectures
          8.0 Communication
                   8.1 Organize and consolidate their mathematical thinking
to communicate with others
                   8.3 Extend their mathematical knowledge by considering
the thinking and strategies of others
          9.0 Connections
                   9.3 Recognize, use, and learn about mathematics in
contexts outside of mathematics
          10.0 Representation
                  10.1 Create and use representations to organize, record,
and communicate mathematical ideas 
International Technology Education Association Standards:
1.0  The Nature of Technology
1.2  Students will develop an understanding of the core  
    concepts of technology.
1.3  Students will develop an understanding of the
    relationships among technologies and connections
between technology and other fields of study.
2.0  Technology and Society
2.2  Students will develop an understanding of the effects
of technology on the environment.
2.4  Students will develop an understanding of the
influence of technology on history.
3.0  Design
3.1  Students will develop an understanding of the
attributes of design.    
3.2  Students will develop an understanding of
engineering design.
3.3  Students will develop an understanding of the role of
troubleshooting, research and development,
invention and innovation, and experimentation in problem solving.
4.0  Abilities for a Technological World
4.1  Students will develop the abilities necessary to apply
the design process.
4.2  Students will develop the abilities to use and maintain
technological products and systems.
4.3  Students will develop the abilities to assess the
impact of products and systems.
5.0  The Designed World
5.4  Students will develop an understanding of and be
able to select and use information and communication technologies.
5.7  Students will develop an understanding of and be
able to select and use construction technologies.
Created by: Steve Rogers, Walker Career Center
Design of Highway Bridges: Based on AASHTO LRFD Bridge Design Specifications. (1997) Barker, Richard, Puckett, Jay. John Wiley & Sons, INC, New York.
Bridge Engineering: Design, Rehabilitation, and Maintenance of Modern Highway Bridges. (1995) Tonias, Demetrios E. McGraw-Hill INC, New York.
Standard Specifications for Highway Bridges. 17th Ed. 2002. American Association of State Highway and Transportation Office (AASHTO).