POE@BHS-Unit 2: Materials and Structures, Topic 2.1 Statics Page 31
Lesson 2.1.G: Truss Design, Construction, and Testing
BALSA WOOD EXAMPLES:
Purpose: To compare the performance of a simple beam and an equilateral triangle truss under small loads.
Materials: 36 in x 1/8 th
in
2
balsa wood, exacto knife, hot glue, 1.00 kg mass
Structure #1 - The 20.0 cm simple beam:

Cut a 20.0 cm section of your balsa wood.

Support each end and hang the 1.00 kg mass from the midpoint of the beam.

Sketch the beam and explain what you observe:
Name: Date Completed:
Initials:
Preliminary
Grade:
Final
Grade:
Grader
Initials:

POE@BHS-Unit 2: Materials and Structures, Topic 2.1 Statics Page 32
Structure #2 – The 7 member equilateral triangle truss:

Cut seven 10.0 cm sections from your balsa wood.

Arrange the pieces of balsa to form a triangular truss, trim to fit, and hot glue the truss together.

Support each end and hang the 1.00 kg mass from the midpoint of the truss (use a paperclip if necessary).

Sketch your truss and explain what you observe:

Apply the graphical method from Lesson 3.4 to each of the joints in the 7-member equilateral triangle truss to determine the force in each member of the truss. Indicate whether the members are in tension or compression. Perform your analysis on a single sheet of graph paper.

Use MD Solids or the Johns Hopkins University Johns Hopkins University web-served software to construct a triangular truss and determine the forces in each member of the truss. Print out the result and turn it in along with a description of the ease with which you were able to use the software.

Compare and contrast the results of your graphical and software analysis. Include at least two advantages and disadvantages of each method of analysis.
Name: Date Completed:
Initials:
Preliminary
Grade:
Final
Grade:
Grader
Initials:

POE@BHS-Unit 2: Materials and Structures, Topic 2.1 Statics Page 33
Structure #3 – Enhanced equilateral triangle truss:

Use the balsa wood provided by your teacher to reinforce Structure #2 within the constraints set forth by your teacher.

Arrange the pieces of balsa to form a triangular truss, trim to fit, and hot glue the truss together.

Support each end and hang the as much mass as possible from the midpoint of the truss
(use a bungee cord to connect the masses to the truss). Indicate the mass of your truss as well as the maximum load held by your truss.
Mass: ___________________ g; Load held by truss: ________________ kg

Sketch your truss and explain what you observe:
Name: Date Completed:
Initials:
Preliminary
Grade:
Final
Grade:
Grader
Initials:

POE@BHS-Unit 2: Materials and Structures, Topic 2.1 Statics Page 34
Structure#4 – Self-directed truss design activity:
Purpose: To design and build a balsa wood truss that has a total mass less than 20.0 grams, is
12 cm long, no more than 3 cm tall and no more than 3 cm wide using just balsa wood and commercially available adhesive. The design must be based upon analysis using either MD
Solids or the Johns Hopkins University Truss Design software. The truss will be tested using the
Structural Stress Analyzer by placing it along a 10 cm span and applying a force hydraulically to the top center of the truss until the truss fails. The performance of the truss will be quantified by taking the ratio of the largest *effective* mass supported by the truss divided by the trusses mass.
Materials: Balsa wood and commercially available adhesive(s).
Type of Project: Individual based
Recommended Resource: http://www.garrettsbridges.com/design/trussdesign (and related)
Assessment: Based upon preliminary analysis (5 points), final design selection (5 points), construction (20 points), performance of final truss (10 points), and reflection on truss design and performance (10 points).
Schedule:

Due: __________ - related solutions, preliminary analysis

Due: __________ - refine ideas, submit design for approval, begin construction

Due: __________ - continue construction, turn in design and truss by the end of class period.

Due: __________ - submit documentation, mass truss, test truss and begin reflection

Due: __________ - due date for reflection
Name: Date Completed:
Initials:
Preliminary
Grade:
Final
Grade:
Grader
Initials:

POE@BHS-Unit 2: Materials and Structures, Topic 2.1 Statics Page 35
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Name: Date Completed:
Initials:
Preliminary
Grade:
Final
Grade:
Grader
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POE@BHS-Unit 2: Materials and Structures, Topic 2.1 Statics Page 36
ACROSS
1 A body subjected to a push.
6 The geometric center of an area.
9 Slender straight pieces of a truss connected by joints.
10 A support that only prevents a beam from translating in one direction.
14 A physical quantity that has magnitude only.
15 A support that prevents translation and rotation in a beam.
17 The resultant of a system of force is the vector sum of all forces.
20 A diagram used to isolate a body from its environment, show ing all external forces acting upon it.
21 The connection points of members of a truss.
22 A broad ridge or pair of ridges projecting at a right angle from the edge of a structural shape in order to strengthen or stiffen it.
23 A method of analysis of trusses w hich constructs free body diagrams of each joint and determines the forces acting in that joint by considering equilibrium of the joint pin.
24 A quantity that has both a magnitude and direction.
27 The direction of a vector is defined by the angle betw een a reference axis and the arrow ’s line of direction.
28 A strong rope usually, usually made of metal, designed to have great tensile strength and to be used in structures.
29 If one body exerts a force on a second body then the second body exerts a force on the first body w hich is equal in magnitude, opposite in direction and collinear.
30 A truss composed of triangles, w hich w ill retain its shape even w hen removed from supports.
31 A condition w here there are no net external forces acting upon a particle or rigid body and the body remains at rest or continues at a constant velocity.
common point on the body or having their lines of action w ith a common intersection point.
11 A truss that lies in a single often used to support roofs and bridges.
12 body subjected to a pull.
13 A surface or shape exposed by making a straight cut through something at right angles to the axis.
16 The sense of a vector is indicated by the arrow .
18 The change of motion of the body is proportional to the net force imposed on the body and is in the direction of the net force.
19 A mathematical property of a cross-section that is concerned w ith a surface area and how that area is distributed about a centroidal axis.
25 A plate or bracket for strengthening an angle in framew ork.
26 The turning effect of a force about a point equal to the magnitude of the force times the perpendicular distance from the point to the line of action from the force.
DOWN
2 The absolute value of a number.
3 A structure or body w hich is over-constrained such that there are more unknow n supports than there are equations of static equilibrium.
4 Something made up of interdependent parts in a definite pattern of organization, such as trusses, frames, or machines.
5 A support that prevents translation in any direction.
7 Every body or particle continues at a state of rest or uniform motion in a straight line, unless it is compelled to change that state by forces acting upon it.
8 A force system w here all the forces are applied at a
Name: Date Completed:
Initials:
Preliminary
Grade:
Final
Grade:
Grader
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