1
Tower Design Project
OBJECTIVES:
1. Learn basic engineering principles.
2. Identify basic shapes that form structures.
3. Design a tower for structural strength that will hold weight.
4. Use the student made design to construct a tower using given materials.
Students will work in groups of two to design and build a balsa wood tower. The tower will be
tested until failure to see how much weight it will hold.
RESOURCES:
www.trebuchet.com
wikipedia.org
INTRODUCTION
A tower is an exceptionally tall building or part of a building or an exceptionally tall structure
used for some functional purpose. In the past, towers were usually used to house bells (bell
towers), for observation (watch towers) or for signaling (light houses) (Scrudder, 2009).
Perhaps the earliest record of a tower comes from the Bible where the story of the tower of Babel
is told. Other notable towers include the Tower of Pisa and Eiffel Tower, two completely
different types of towers. Today there are many more types of towers which are used for a wide
variety of functions. A few examples are transmission line towers, radar towers, radio and TV
broadcasting towers, even towers for suspension bridges (San Joaquin Expanding Your
Horizons, n.d.).
BASIC ENGINEERING PRINCIPLES AND DEFINITIONS
Tension: the action of being stretched to stiffness
Compression: the action of being pressed or squeezed
Weight: a load with a certain heaviness, a specific force due to gravity
Support: to hold up or serve as a foundation
Tensile Strength: the greatest stress a substance can bear without tearing apart
2
Butt Joint: A technique in which two members are joined by simply butting them together. The
butt joint is the simplest joint to make since it merely involves cutting the members to the
appropriate length and butting them together. It is also the weakest because unless some form of
reinforcement is used it relies upon glue alone to hold it together. Because the orientation of the
members usually presents only end grain to long grain gluing surface, the resulting joint is
inherently weak.
Lap Joint: In woodworking, a lap joint describes a technique for joining two pieces of material
by overlapping them. Usually, no material is removed from either of the members to be joined,
resulting in a joint which is the combined thickness of the two members.
BASIC STRUCTURAL SHAPES
triangles - rigidity of the triangular shape can support weight securely
squares - can support weight, but can twist and collapse if not supported
polygons - like squares, can support some weight, but will twist and collapse if not supported.
TIPS FOR STRUCTURE: The best advice for building structures starts with commitment.
Your dedication and attention to detail is the winning combination. The following list of tips will
help you succeed but only if you are dedicated to the project. Be sure you understand the event
rules before designing your prototype.
1) Draw your preliminary design with full wood outlines. This should help you to decide
whether to use butt joints or lap joints.
2) ALL joints should have absolutely flush surfaces before applying glue. Anytime glue is
used as a "gap filler", it dooms the structure! Cut the wood precisely and carefully sand the part
so that it fits flush. Then, number the part and use it as a template to make numbered duplicates
in assembly sequence (i.e.: two for bridges, four for towers).
3) Structures are symmetric. When building a bridge or a tower with two or four sides, build
the two primary sides one on top of the other. Once the first side is built, cover it with wax paper
and build the second side directly on top of the first. This helps insure the structure's
symmetric integrity.
4) Up to 20% of the structure's mass may be from over gluing. Adhesives do not work better
when they are drooled all over the structure. Use the adhesives sparingly where any more than a
translucent, moist surface becomes wasted, excess mass.
3
Materials and Specifications
1. The tower must be constructed ONLY from the following materials:
-21 ft. of 1/8" x 1/8" balsa wood
-non-toxic glue
2. Equipment:
-one cardboard work area
-wax paper to cover the drawing during construction
-straight pins (to hold wood in place while the glue dries)
-one X-acto knife
3. Specifications:
-Over-all tower size height: 12" (a 1/2" tolerance will be allowed without deductions.)
4. The tower must support a target weight of 60lbs.
5. Limitations:
A. Only balsawood and non-toxic glue will be used.
B. Wood cannot be treated in any way to change its strength or appearance.
C. Only the amount and type of materials specified will be used in the tower.
D. Wood pieces may be bonded together with glue ONLY at joints.
E. Splitting or laminating are not allowed.
GOAL
Build a tower that holds a weight of exactly 60lbs.
Having the greatest efficiency rating.
STRESS TEST A TOWER
A. Tools and Materials
1. Completed tower (allow overnight drying time)
2. Testing equipment (provided by Instructor)
a. Testing block
b. Weights (various sizes)
c. Calculator
d. Tower support device
B. Procedure
1.
2.
3.
4.
Check tower to see that it meets all specifications.
Compare tower to drawings.
Measure weight of tower and record.
Place tower on support system.
4
5. Place testing block on top of tower.
6. Place weight on testing block in even, increasing measurements by sliding them on top of the
testing block, then carefully lowering the testing block to rest on the tower.
8. Continue until the tower (breaks).
9. Determine weight held (test block, weights)
10. Calculate efficiency using the following equalizing formula:
Efficiency = Failure Weight / Tower Weight
11. Clean up test area.
References
Scrudder, N.R. (2009). Engineering structures: Balsa wood tower. Carrollton-Farmers Branch
Independent School District, Carrollton, TX . Retrieved August 19, 2009 from
http://cfbstaff.cfbisd.edu/scrudderr/Tower/towers.htm
San Joaquin Expanding Your Horizons. (n.d.) MESA: The paper tower. Retrieved August 19,
2009 from https://sjeyh.org/ThePaperTower.pdf
Note* -- much of this material is take directly from the references listed. It appears that one of
the references actually utilized materials of the other. We are not sure who used the information
first so we are crediting both in a general statement and doing as Dr. Harry Wong suggests for
education purposes, stealing. Please cite these references as they are the original creators or
thieves.
5
Grading Rubric: Tower Design Project
Name 1: __________________________________________________
Date: __________
Name 2: __________________________________________________
1.
2.
Description
Possible
Design/Engineering Log:
a. Following the engineering design process
b. Thoroughness
c. Design
d. Collaboration
20%
_____
40%
_____
5 pts.
5 pts.
5 pts.
5 pts.
Weight Held:
a.
b.
c.
d.
e.
f.
60 lbs +
55 – 59 lbs
50 – 54 lbs
45 – 49 lbs
40 – 45 lbs
39 – lbs and below
Received
40 pts.
35 pts.
30 pts.
25 pts.
20 pts.
10 pts.
3.
Efficiency:
(Calculate Efficiency Here!)
20%
_____
4.
Redesign/Reflection:
20%
_____
a.
b.
c.
d.
e.
Great Redesign and reflection
Above average redesign and reflection
Average redesign and reflection
A redesign or a reflection
No redesign or reflection
20 pts.
15 pts.
10 pts.
5 pts.
0 pts.
Total Score
_____
6