Oak Valley Middle School

Science Olympiad Elevated Bridge

Coach: Jay Trischman

Phone: 858-312-1342 (home) 858-472-5651 (cell)

E-mail: trischman2@cox.net

trischmanj@saic.com

What is the Elevated Bridge Event ?

• Teams of 2 will build a bridge prior to the competition.

• It must be constructed only of wood bonded by glue

• It must meet a set of size limits listed in the rules

• During the competition, you will test how much weight the bridge will hold

• You will add weight until it reaches 15 kg or until the bridge breaks

• Score = weight held divided by the bridge’s weight

Strength and Weight are Equally Important

Bridge Dimensions - 2010

20 cm 15 cm

20 cm opening

Loading Block

Chain

Sand Bucket (not to scale)

Test Platform

Also see drawing at: http://soinc.org/elevated_bridge_b

35 cm span

5 cm bearing zone

5 cm

15 cm clear area

Size Rules• Bridge must span at least 35 cm• Bridge can touch test surface only in “bearing zone” 5

cm on either side of span• Bridge must be less than 20 cm high• Bridge must have clearance for 15 cm x 15 cm block• Bridge must support 5 cm x 5 cm loading block centered

over opening• Bridge must provide space for a chain or rod to extend

below loading block• There is no restriction on the width of the bridge

Bridges that don’t meet the rules are penalized

Materials

• The bridge must be built of wood only– No bamboo, paper, particle board, composite

material, or pre-laminated wood– We will have Balsa wood for you to use– You can get other types may be from hobby and

craft stores – Thin pieces can be laminated (glued together in

layers) to create stronger, thicker pieces if needed

Remember, weight is important

Glue

• Any kind of glue can be used– “Super” glue is strong and dries quickly

( Use sparingly and Don’t glue your fingers together )

– White wood glue (must dry overnight)

Remember, weight is important

Designing Your Bridge• Designing means creating plans of how your bridge will

look and be built• Look for ideas in structures you see around you• The bridge must be elevated, so it might look different from

the winners in other contests.• The bridge must be light and strong; you probably want to

use a truss design

Tower Bridge Truss Bridge

Your Design Ideas

• Start with sketches in a notebook• Include notes about how thick each piece should be• After the bridge is built and tested you will add notes

about what works and what doesn’t work• Your plans and notes let you rebuild a bridge that

breaks• You can also make improvements each time so each

bridge is better than the last

Hints: Building A Strong Bridge

• The vertical pieces are called columns• Columns break by buckling (bending in

the middle) when loaded

• To prevent buckling, attach cross-pieces to the columns

• The angled pieces give stiffness by forming triangles

Weight

Buckling

Triangles are your friend !

Truss Design• A truss is a structure made of straight thin members

connected to each other, usually forming triangles• Each member (piece) of a truss is either

– under Compression (being squeezed) or– under Tension (being stretched)

• Computer programs can tell you the amount and type of forces in each member of a truss

Example Truss Analysis

-15 -10 -5 0 5 10 15

2

4

6

8

10

12

14

-0 55

-178

-55

156

-133

55

111

-55

-89

55

67

-82 82

-19

-29 76

0

178

-178

55

156

-55

-133

55

111

-55

-89

67

55-69

-27

69

-1260

length, cm

He

igh

t, c

m

Load

Red pieces are under compression, black are under tension.Higher numbers mean larger force.

Construction Hints• The side sections (trusses) of your bridge can be built on

top of your full-sized plans– Tape the plans to a piece of cardboard– Cover the plans with wax paper– Cut wood and check sizes against the plans– Use tape or pins on either side of the wood strips to hold them

while the glue dries

Construction• Build two identical trusses and attach them together• One approach is to use stacks of books and tape to hold

the trusses in place• Make sure the spacing and alignment is exact and the

trusses are vertical• Glue in cross pieces on each end and the top• Once these have dried, remove the books and add the

rest of the cross supports

Competition – Set up

• On competition day the Bridges are weighed and placed on a test stand

• The loading block with a chain or rod attached is put in place …

Competition - Loading

The student adds sand to a bucket suspended from the bridge until the bridge breaks or the maximum weight (15 kg.) is reached.

The loading technique is important too!

Testing

• The best way to learn what works is to build bridges and then break them !

• Each failure teaches us something

On-line Resources

• The Science Olympiad Site:http://soinc.org/elevated_bridge_b

• Truss designerhttp://www.jhu.edu/virtlab/bridge/bridge.htm

• Some pictures and ideas:http://www.bridgesite.com/funand.htm

• Check out YouTube to see videos of bridges being tested

• Notes that some bridge contests have different rules

Meetings / Practices

• Competition: Saturday, Feb 6, 2009 atBernardo Middle School

• Meeting / Building Sessions:– Place: Trischman House - 9647 Deer Trail Dr.– Days: Wednesday (alternating weeks)– Time: 4:30 – 6:00 pm

• Possible Dates: – Oct 14, Oct 28, Nov 11, Dec 9, …– These weeks fall on Thanksgiving and Christmas

• What are you conflicts and preferences?