How to build a bridge!

This slideshow contains tips, hints and several interesting bridge designs.

The Romans frequently built bridges with several small arches on top of one another.

Tools and Equipment

• Not all of this is necessary, but all of it is very helpful.

“One only needs two tools in life: WD-40 to make things go, and duct tape to make them stop.”

-G. Weilacher

• Most glue is stronger than the wood itself• As long as you use glue for what is was

designed it might not really matter

Use the glue you are given!

CA Glue (aka superglue) – High School Use

• Dries quickly• Very strong• Comes off your

fingers naturally within two weeks

• Must use in a ventilated area

Excellent for gluing two sides together!

Wood Glue – Middle School Use

• Good brand of wood glue

• Three types available

• Clamp for ½ hour

• Water clean up

• Excellent for laminating beams together

Tools

• All of these tools are recommended but be careful as they are sharp and can injury you if used improperly.

• Scissors, ruler, square, level, and sharp blades

More tools

• Binder clips make excellent clamps (and are cheap)

• You need a sanding block and plenty of sandpaper.

Even more tools…

• Files will help you to shape the wood.

• Pins are available at hobby stores. You must have many.

A 3/32” square file is particularly helpful in making notched joints.

• A ceiling tile works very well to build on. It provides a level surface that you can pin into.

• Alternatively, you can use several sheets of cardboard stacked together.

• This is a ceiling tile that has been glued to a thin piece of wood.

• The wood keeps it level and prevents pins from pushing through.

How To Build Your Bridge

Planning

• The success of your bridge is roughly 50% design and 50% construction!

• A full scale template is highly suggested.• Use a ruler and make your plan full scale

and symmetric• Glue sticks together to make an actual-

size ruler – two thick, three thick, etc.

• Tape your full scale plans to the board and pin a piece of wax paper on top. Plan templates are available from me!

• The wax paper prevents the glue from ruining your plans.

• Glued joints will be stronger if you pre-sand all of the wood.

• Choose the best pieces of wood for the vertical and horizontal major components.

• Darker wood tends to be brittle but stronger.

Use your balsa sticks wisely as you can only use the materials you are given.

Construction

• Take care to make good joints.• When you are done, gently sand it.• Extra glue adds weight, but not strength.• Make sure to follow the gluing directions!• Take your time!• CA glue is a solvent for itself. That means

if the glue has cured, don’t add more or it will dissolve itself.

• Make the beams first.

• Each beam is clamped with binder clips

• Alternate the clips so that the beam does not warp

• Sand each beam until it is flat after it dries

• Make each side one at a time

• The aluminum pins are available at any hardware store

• Don’t pin through the wood!

• Complete each side and then remove it from the wax paper

• Leave the pins in place for the second side to insure that they are identical

• Put the sides together and cross brace them

• Note that this design has an undertruss which is not allowed in this year’s competition!

• Sand the entire bridge!

• Insert gussets where needed

Baking Your Bridge!

• You can loose A LOT of water mass by baking your bridge!

• Low setting for about 15 minutes

• Seal in a plastic bag after baking Bake at your own risk!

Bending Wood• To bend wood, soften

it first over boiling water.

• Steam softens wood.• Bend, pin in place

and let it dry.• After dry, glue it• Be very careful not to

burn yourself or your teammates! Never pin through the wood!

Truss Designs

Warren Truss

Pratt Truss

Howe Truss

K Truss

Types of Joints

End joint

(weak)

Notched Joint

(better)

Lap Joint

(best)

Gussets improve a joint

Loading your bridge• You have 5

minutes to place your bridge on the load frame and position it with the loading bucket.

• You have 20 minutes to load your bridge to failure.

Good Luck!• Bridges are rated on efficiency.• Your bridge needs to be light and strong!• Awards are given for the top 3 teams in

both divisions.• Judge’s Choice award will be given at the

discretion of the judges.• The high school winner may receive a

$1000 scholarship if they choose to enroll at UMKC in the School of Computing and Engineering!