Toothpick bridge basic rules
Bridge built using ordinary flat toothpicks and white glue.
Bridge must be freestanding, and span a gap of 30 cm.
Roadway level, at least 5 cm wide and 30 cm long.
Glue unlimited :D
When your bridge is tested, it will 'fail' when the roadway breaks, or flexes more than 2 cm.
Instructions
EACH STUDENT WILL RESEARCH BRIDGE DESIGNS FROM LITERATURE OR ACTUAL STRUCTURES NOTING BRACING POINTS AND REINFORCEMENTS AND HOW EACH DESIGN TAKES INTO ACCOUNT GRAVITATIONAL AND LOAD FORCES AND THE MATERIALS USED. EACH STUDENT WILL THEN DESIGN AND BUILD A BRIDGE USING WOODEN TOOTHPICKS AND ELMER'S WHITE GLUE
Specifications
THE TOTAL WEIGHT OF THE FINISHED BRIDGE CANNOT EXCEED 40 gm
ANY DESIGN CAN BE USED AS LONG AS THE ROADBED IS FLAT AND UNOBSTRUCTED TO ALLOW A MATCHBOX CAR TO TRAVEL ITS LENGTH.
THE BRIDGE MUST BE FREE STANDING AND ALLOW FOR A 2 cm X 30 cm BOARD TO PASS UNDER THE BRIDGE WHILE IT RESTS ON A FLAT SURFACE.
ONLY THE MATERIALS LISTED MAY BE USED TO BUILD THE BRIDGE.
EXCESSIVE AMOUNTS OF GLUE MAY NOT BE USED AS PART OF THE STRUCTURE, i.e. THE BRIDGE MAY NOT BE COMPLETELY COVERED WITH GLUE.
Procedure
TO TEST EACH BRIDGE'S STRENGTH WE WILL PLACE THE BRIDGE ONTO AND BETWEEN TWO FLATTOPPED TABLES SPACED 25 cm APART.
AN 8" WOODEN DOWEL WITH A 1/2" DIAMETER IS SET ACROSS THE MIDDLE OF THE ROADBED. TWO LOOPS OF STRONG CORD ARE ATTACHED TO THE HANDLE OF A 5 gal BUCKET. EACH LOOP OF CORD IS THEN LOOPED OVER EACH END OF THE DOWEL TO SUPPORT THE BUCKET BELOW THE BRIDGE. SAND OR WATER IS ADDED TO THE BUCKET UNTIL THE BRIDGE BREAKS. THE BUCKET AND ITS CONTENTS ARE THEN WEIGHED.
RANKING
EACH BRIDGE WILL BE RANKED USING A RATIO OF LOAD WEIGHT TO BRIDGE WEIGHT.
Lesson Objectives:
Students will understand the importance of proper design.
Students will understand the importance of teamwork.
Students will review the metric conversions, force calculations.
Students will recognize the importance of using reference manuals/materials.
Students will understand the proper way to construct and interpret graphs.
Students will see how physics/science/math relates to an industrial job/proposition.
Materials (per team):
One box standard, wooden toothpicks
One large standard bottle of Elmer’s glue
One large bucket with handle
Water
Bathroom scales
Strong string
Metric ruler
Procedure:
1. In groups of 23 students will design/construct a bridge at least 30 cm long using only one box of toothpicks or less and one bottle of glue or less. The goal is to construct a bridge that will be able to withstand a large amount of weight/force. (This should take one class period.)
2. Students will test each group’s bridge to determine amount of “give” or bend as various amounts of force are applied.

Fill bucket with water, weigh on scales 5, 10, 15, etc. pounds of water.

Place bridge between two table tops and thread string through the bridge

Using a dowel or strong yardstick through bucket handle and string, hang the bucket on the bridge.

Using a smaller metric ruler, measure the “YMAX” or “bend” at each weight and record.
3. Using the provided reference materials, students will calculate

resistant force at point “A”

resistant force at point “B”

and the ymax or “bend” at each weight
4. Students will use calculations to graph Force vs. Deflection (or “bend” or “ymax”)
5. Students will discuss/make conclusions as to the pattern of this bridgebreaking process.
6. Following this activity a speaker would make a presentation concerning teamwork, use of math, science, technology in the workplace.
Weight

Force on Bridge
(calculate N)

Resistance “A” (N)

Resistance “B” (N)

YMAX (“bend”)
(mm or cm)

5





10





15























100(as needed)





Needed equation from reference* Fl^{3}
48 EI
l= length
E = modulus of elasticity (Gpa) (from “Table A7”)
I = moment of intertia (“Table A30—use rectangle) ( bh^{3} )
12
Evaluation:
Check student data and calculations

Bridge Building Code
1. Build the bridge on a piece of cardboard 15 cm by 35 cm.
2. Draw a river, 15 cm wide, in the middle of the cardboard.
3. Draw one 5 cm square at each end of the cardboard, 2.5 cm from the river and 2.5 cm from the edge.
4. Draw and cut a 4 cm square exactly in the center of the cardboard, in the river.
5. Draw plans of the bridge to show four views: the view from one end, the side view, the road bed, and the top view. The plans must be readable, clear, and may not be changed once construction has begun.
6. When building the bridge, apply glue sparingly only to join the toothpicks.
7. The bridge must at all times touch only the cardboard inside the drawn squares. Toothpicks may be glued into holes punched in the cardboard inside the squares.
8. The bridge must be more than 5 cm high. This distance is measured from the cardboard to where the deck of the bridge would be. The tag board boat, 5cm tall, must be able to travel the length of the river.
9. The bridge must be at least 4 cm wide. The tag board truck, 3.5 cm wide, must be able to travel the length of the road, if the bridge had a deck.
Bridge Construction – Contest Rules
1) The bridge must be built according to the bridge building code, using only materials supplied by the I.S.O. Lumber Company Warehouse.
2) The bridge will be judged for the quality of the building plans and the strength of the bridge.
a) Judging of the building plans will consider neatness of the finished bridge, how well the finished bridge matches its plans, and cost of the bridge.
b) The bridge will be tested for strength by placing a bar across the middle of the bridge and hanging weights from the bar.
i) The teacher will suspend weights from the bridge according to the project director’s wishes.
ii) The last weight that the bridge holds for 30 seconds without touching the cardboard in any spot (except at the bridge foundation) is the weight recorded for the strength of the bridge.
iii) Calculate the strength (mass supported) to mass of the bridge ratio.
Bridge Truss Designs
Be able to identify these types of bridge trusses:

PRATT


CURVED CHORD
PRATT


BALTIMORE


PENNSYLVANIA(PRATT)


WARREN W/O VERTICAL
SUPPORTS


WARREN WITH VERTICAL
SUPPORTS


QUADRANGULAR
WARREN


SUBDIVIDED WARREN
TYPE


SUBDIVIDED WARREN
TYPE


LATTICE


WHIPPLE

