Transcript How to build a bridge

How to build a
bridge
The Romans
frequently built
bridges with
several small
arches on top of
one another.
This slideshow contains tips, hints and
several interesting bridge designs.
You may use what you like. I will post
this on my website for you to view
later.
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
What glue
should you
use?
• Most glue is stronger than the wood itself
• As long as you use glue for what is was
designed it might not really matter
• Different glues do have different advantages…
CA Glue (aka superglue)
• Dries quickly
• Very strong
• Don’t get cheap
superglue
• Comes off your
fingers naturally
within two weeks
• Accelerators
available
• Must use in a
ventilated area
Excellent for gluing two
sides together!
Titebond (I,II and III)
•Good brand of wood
glue
•Three types available
•Clamp for ½ hour
•Water clean up
•Excellent for
laminating beams
together
Gorilla Glue
•Claimed to be very strong
•Expands while drying
•Takes 24 hours to dry
•Longer set time
•I wouldn’t use it.
Epoxy – the mother of all glues!
•Incredibly strong
•Relatively heavy
•Difficult to work with
•Available with different
working times
•Skin contact is bad
•Good for laminating
sticks together
Tools
•All of these tools are recommended.
•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.
You may need an assistant!
For playing with knives…
•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.
• 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.
How To Build Your Bridge
Planning
• Planning is good!
• I will provide a full scale template
• Use a ruler and make your plan full scale
and symmetric
• Glue sticks together to make an actualsize 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.
I buy 20 sticks.
You buy more if
you need it.
I have more for
sale!
• Glued joints will be stronger if you pre-sand all
of the wood.
• Choose the best pieces of wood.
• Darker wood tends to be brittle but stronger.
Balsa Wood
Bass Wood
• Don’t get the wrong wood!
• Balsa is much less dense and scratches much
easier.
• The bins at local suppliers are often mixed up.
Construction
• Take care to make good joints.
• When you are done, sand the heck out of
it!
• Extra glue adds weight, but not strength.
• Make sure to follow the gluing directions!
• Take your time!
• I made all of the
beams first
• Each beam is
clamped with binder
clips
• Alternate the clips
so that the beam
does not warp
• I used Titebond III
for the beams
• Sand each beam
until it is flat after it
dries
• Make each side
one at a time
• I used CA glue to
glue in the cross
braces
• The aluminum
rods 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
•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
Never pin through the wood!
Truss Designs
Howe Truss
Warren Truss
K Truss
Pratt Truss
Types of Joints
Gussets improve
a joint
End joint
(weak)
Lap Joint
(best)
Notched Joint
(better)
Interesting Designs
Arch
Elevated Beam
Scissor Truss
Loading your bridge
• This year, we will load each bridge with a 40
mm square steel plate that is 10 mm thick.
• The plate is attached to a 3/8” steel rod.
• We will load the bridge in one of three places
– the center or 50 mm on either side.
• The load point will be chosen randomly.
• You will load the bridge until it fails.
• Highest efficiency wins.
Good Luck!
• Bridges are rated on efficiency.
• Your bridge needs to be light and strong!
• The top five students at MVHS will go on
to the regional competition in Bellingham.
• The top two in Bellingham will go to the
National Competition in Chicago.
• The winner at the international contest will
be awarded a half-time scholarship to the
Illinois Institute of Technology!