Structural engineer

Be a Structural Engineer!

The unit introduces elementary age students to processes involved in designing and building things, with a focus on structural strength. The approach to student learning is one of discovery, followed by presentation and clarification of concepts. Evaluation is based on teacher observation of the students as they work both alone and in groups. Formal assessment is tied to the rubrics that evaluate the design, process, and testing of the students final truss-building projects.

TitleIII Technology Literacy Challenge Grant

Learning Unit

Overview | Content Knowledge | Essential Questions | Connection To Standards | Initiating Activity | Learning Experiences | Culminating Performance | Pre-Requisite Skills | Modifications | Schedule/Time Plan | Technology Use

LU Title: Be a Structural Engineer!Author(s): Jim Dever
Grade Level: 4-5School : New York Mills Elementary
Topic/Subject Area: EngineeringAddress: 1 Marauder Blvd., NY Mills
Email: jdever@ny-mills-csd.moric.org

Overview

The purpose of this unit is to introduce elementary age students to some of the processes involved in designing and building things with a focus on structural strength. This is done through a series of projects.

Although the emphasis of this unit is on Learning Standard 5 (Technology), this unit also has strong ties to MST Standard 1 (Analysis, Inquiry, and Design), and Standard 7 (Interdisciplinary Problem Solving).

The general approach to student learning is one of discovery, followed by presentation and clarification of basic concepts. Evaluation takes place throughout the unit via teacher observation of the students as they work both alone and in groups. Formal assessment is tied to the rubrics which evaluate the design, process, and testing of the students final truss-building projects. 

Content Knowledge

DeclarativeProcedural
 Students will know what an engineer’s job involves. Students will be able to measure distances.
 Students will be able to identify the four basic bridge types. Students will be able to take data and produce a graph of it.
 Students will understand the meaning of ‘tension’ and ‘compression’ as forces in a structure. Students will be able to gather data and make hypotheses.
Students will know the general properties of different building materials. Students will be able to work as a team to create models and evaluate them bases on specified criteria.
 Students will be able to define what a ‘truss’ is. Students will be able to discuss the advantages and disadvantages of particular truss designs.
 Students will be able to identify truss applications in everyday life. 

Essential Questions

 What does an engineer do?

What factors are important in structural design?

What are the qualities of different materials used in construction?

What is the process involved in designing and manufacturing a truss?

Connections to NYS Learning Standards

Standard 5 – Technology

1. Engineering design is an iterative process involving modeling and optimization used to develop technological solutions to problems within given constraints.

2. Technological tools, materials, and other resources should be selected on the basis of safety, cost, availability, appropriateness, and environmental impact; technological processes change energy, information, and material resources into more useful forms.

3. Computers as tools for design, modeling, information processing, communication, and system control, have greatly increased human productivity and knowledge.

7. Project management is essential to ensuring that technological endeavors are profitable and that products and systems are of high quality and built safely, on schedule, and within budget.

Initiating Activity

Building for Strength

Students will be introduced to the job functions of an architect and an engineer, including what their roles would be on a project, and the importance of their having to work together. (Architect – a person who plans and designs things to be built with an interest in its appearance. Engineer – a person who can develop the best way to build something considering cost, strength, time, etc.)

Each student will then make a choice to be either an architect or an engineer. ‘Architects’ and ‘engineers’ will be paired to work on their first building project. Review the project guidelines below and pass out the project sheet with the specified materials to work with.

Project Guidelines: Each group is to create an attractive structure which will support as many textbooks as possible, holding them at least one inch off the table surface. No more than 15 gumdrops, and 25 toothpicks may be used. No more than one toothpick can connect any two gumdrops in the structure. The structure must be one connected object able to support the books for a time of 15 seconds. Projects will be judged on appearance (class rating from 1 to 5), and strength (number of books that can be supported), in the next class session.

Learning Experiences

Day 1: Initiating Activity (‘Building for Strength’ – described above)

Day 2: Testing and Evaluation of the Gum Drop projects

Each group will receive a project evaluation worksheet with the names of each team’s project on the sheet. At this time each group will rate all of the other groups projects on ‘appearance’, and also make a prediction as to how many books they believe each structure will be able to hold.

Projects will then be tested in this way. First one text book will be placed on the structure, followed by another book every 15 seconds, until it either collapses, or the books come within one inch of the table. It must hold the books for at least 15 seconds to receive credit for supporting the additional book. Each group will record the score of every other group, and produce a graph of the strength results with an average score.

Finally, groups will be asked to comment on their observations as to what factors appear to most significantly contribute to strength.

Day 3: Choices in Building Materials

Students will be asked to list the products used in building (wood, concrete, steel, plastic, ice, rubber, rope, animal skins, bamboo, grass, etc.), and then discuss where each product might be used, and why. Consider the different things that ‘homes are made of’. This may serve to broaden student’s scope of thinking.

Introduce the qualities of various building materials by defining such terms as strength, rigidity, flexibility, weight, cost, availability, etc.

Conclude the lesson by distributing a matrix for students to complete which asks them to evaluate these different materials in terms of their qualities.

Materials Rating Worksheet (1=low, 2=average, 3=high, 4=very high)

MaterialFlexibilityStrengthDurabilityCostAvail-abilityEase of Use
Wood      
Concrete      
Steel      
Plastic      
Rubber      
Ice      

Day 4: Basic Principles of Strength in Construction

Students will again use toothpicks and gumdrops to construct a series of two-dimensional shapes that they will evaluate for rigidity. From this exercise, students will pair up and write a paragraph explaining their discoveries in the form of advice they would give to someone that would help them to build something that is strong.

Day 5: Introduction to Bridges

Show the class some picture of different types of bridges, and the reason for their design. Demonstrate the advantages of each of the 4 basic bridge structures including ‘truss’, ‘suspension’, ‘arch’, and ‘cantilever’. Show students the concept of compression and tension as being the two forces that act in the members of of different bridges. Have some books from the library available and the materials below to demonstrate ‘tension’ and ‘compression’.

Introduce the report that each student will do on a bridge of his or her choice.

 Day 6 – 7: Bridge Research

Students will use an online encyclopedia, the internet, and the library to collect information about one bridge of their choice. Their report should include a picture of the bridge, an explanation of its purpose, and some basic facts about its history, style, type, and construction.

Day 8: Bridge Building Team Competition

Students will will be grouped in teams with the challenge of attempting to see who can span the greatest unsupported distance using the given materials, and following the guidelines below.

  • No more than 30 gumdrops may be used.
  • Gumdrops may not be cut or divided.
  • Only one toothpick may connect any two gumdrops. (no ‘doubling up’ of toothpicks.
  • The bridge must be able to support a cardboard ‘road’ 1 inch wide and as long as the bridge. It should be able to allow a standard matchbox car to pass over the bridge.
  • The bridge, once placed on 4 inch high supporting blocks, must be able to hold 3 matchbox cars for a period of at least one minute without breaking or touching the ground.
  • Successful bridges will be scored by measuring the distance between the supporting blocks in centimeters.

Day 9: Evaluation of Bridge Projects

Team projects will be presented to the class tested, and measured for the unsupported distance that they can span. Students will identify what type of bridge each group chose to build. Completed projects can be placed in the school display case.

Day 10: Trusses

Define what a ‘truss’ is. A truss is a framework of beams or other supports usually connected in a series of triangles and used to form a support for a roof, bridge, or floor.

Demonstrate the differences between truss construction and traditional construction methods as they relate to roofs and floors.

Show the similarities between truss bridges, and roof and floor trusses. Discuss the advantages and disadvantages of trusses as opposed to traditional construction.

Advantages of trusses: Trusses take less material to have a comparable strength. They can be pre-fabricated in a factory to speed onsite construction. Construction costs are lower because they are faster to install. Trusses do not require center supports and therefore give more flexibility in doing interior design work.

Disadvantages of trusses: Trusses should be professionally constructed to insure proper strength. They reduce or eliminate your opportunity to have attic space. Trusses are not as fire retardant as conventional beams.

Point out the similarity between floor trusses and the bridges that students built. Explain that we are going to begin a new project involving the design of a standard roof truss in our next class.

Day 11-14: Truss Design and Construction Activity (Culminating Activity described below)

Day 15: Field Trip

Class field trip to a local truss manufacturing plant where students see the process of truss building, beginning with the design phase on computers under the direction of an engineer, to the manufacturing of the trusses by assembly line workers, and finally the delivery and installation of the trusses at the construction site.

Culminating Performance

 Truss Design

Working in pairs, students must design a scale model of a truss to be used in a single story house. The scale drawing must be 17 centimeters wide. These drawings can be done using any simple simple painting, drawing, or desktop publishing program on the computer, or if necessary, they can be done with paper and pencil. Students should keep in mind that their truss will be tested for strength as shown below, and it will be evaluated for cost by computing $.35 per foot of wood used, and $.50 for each fastening point (refer to the ‘Cost Analysis Worksheet’).

Truss Construction (1 centimeter = 1 foot)

Every group will replicate their truss following the specifications below:

  • The truss must be peaked in the center, and span 34 centimeters in order to fit into the testing device.
  • It must be made exclusively from straws and tape.
  • Tape may not extend more than one inch from any joint.
  • Straw material will be charged at a cost of $.40 per centimeter and must be ‘purchased’ in whole straws.
  • Tape material will be charged at a fee of $.50 per joint. Students are not to use more than 5 inches of tape in joining any two pieces.
  • Completed trusses will be graded on strength, and on cost of materials.

Completion of Cost Evaluation Worksheets

Each group will complete the cost evaluation worksheet which shows his truss design, and carefully documents all of his materials and final costs.

Strength Testing of the Trusses

Each truss will have a mesh netting placed over it to help to distribute the weights that are added. One team member will then gradually suspend weights on the truss until it eventually collapses. During this process, the other team member will record on their drawing of the truss where its apparent weak spots were, and note any comments related to how the truss reacted to the stress on it.

Student Evaluation

Students will complete a summary chart which ranks all of the trusses in relation to their strength, and their cost with 1 being the lowest. Final rankings are added to determine the winning truss.

Evaluation Rubric 

 321
Design ProcessThoughtful planning, accurate scale drawing, significant attention to detail, and good use of concepts learned.Some signs of planning, and application of the concepts studied related to trusses.Little evidence of planning, poorly drawn diagram, showing little or no application of concepts learned.
ConstructionAccurately matches the drawing, joints are neatly done.Minor differences between the drawing and the finished product.Significantly different than the drawing, sloppily put together.
TeamworkStudents worked together and took advantage of each other’s abilities.Either one student dominated the group, or one or more students did not engage in the work.Students failed to work well together.
Cost ComputationWorksheet neatly and accurately completed.Minor errors in either measuring or computation of the cost of the truss.Major errors in the measuring of materials, and the related calculations.
Testing ProcessGood judgement demonstrated in the addition of stress to their truss.Students showed a limited understanding of how to apply force to their truss.Students showed little understanding of how to best apply stress to their truss.
Summary and Self-evaluationShowed the ability to work within constraints, and the ability to develop modifications based on observations.Limited ability to develop modifications and draw conclusions.Students did not demonstrate that they learned anything beyond what what was initially told to them.

Prerequisite Skills

It is helpful, but not essential, that students know how to use an electronic encyclopedia, and a desktop publishing program. Students need to be able to measure in centimeters, average numbers, and do the basic operations with decimal numbers. Students should also be able to write a simple report in standard format.

Modifications

No modifications were necessary with the group that we worked with. Because much of the work is done in groups, it is easy to provide help for students with the majority of handicapping problems.

Unit Schedule / Time Plan

Lessons are designed for 30 to 45 minutes each, but can be easily modified to longer time periods if they are available. This project can generally be completed in one month by having classes three times per week.

Technology Use

  1. Students will use an electronic encyclopedia, and the internet to do their bridge research project.
  2. Students will use a spreadsheet program to graph the results of the bridge building project.
  3. Students will produce a design for their ‘truss’ by using a desktop publishing program.
  4. Students will use a spreadsheet program to produce a graph showing the results of the strength, and cost evaluations for the trusses tested.

Related Web Sites

https://www.pbs.org/wgbh/nova/bridge/build.html

http://www.pbs.org/wgbh/nova/lostempires/china/miracle.html

https://pages.jh.edu/~virtlab/virtlab.html

Further reading: How to Write a Lesson Plan: 7 Steps