Transcript Paper Truss Bridge

Paper Truss Bridge
MESA Day 2010 Competition
Intro To Truss Bridges
• A truss bridge uses a triangle based lattice work
design to add rigidity to the supporting beams,
greatly increasing their ability to dissipate
compression and tension. Once the beam begins
to compress, the force is dissipated through the
truss.
How Truss Bridges Work
• In a beam bridge, the top of the beam has the
most compression, the bottom the most tension,
and the middle very little of either.
• If you look at the truss as a single beam, the
majority of your material is at the top and
bottom, creating more rigidity where it takes on
the most force.
How Truss Bridges Work
• Additionally, the use of triangles within the truss
allows it to dissipate the load throughout the
truss work.
Types of Truss Bridges
• 3 main types of truss bridges
– Through Truss – traffic travels through the lattice
work structure
– Deck Truss – traffic travels above the lattice work
structure
– Pony Truss – traffic travels between the lattice
work structure
Popular Designs
WARREN TRUSS
• The Warren truss is perhaps the most common truss for both simple and
continuous trusses. For smaller spans, no vertical members are used
lending the structure a simple look (illustration #1.) For longer spans
vertical members are added providing extra strength (illustration #2.)
1
2
Matsuo Bridge Company - http://www.matsuo-bridge.co.jp/english/bridges/basics/truss.shtm
Popular Designs
PRATT TRUSS
• The Pratt truss is identified by its diagonal members which, except for the
very end ones, all slant down and in toward the center of the span. Except
for those diagonal members near the center, all the diagonal members are
subject to tension forces only while the shorter vertical members handle
the compressive forces. This allows for thinner diagonal members
resulting in a more economic design.
Matsuo Bridge Company - http://www.matsuo-bridge.co.jp/english/bridges/basics/truss.shtm
Popular Designs
HOWE TRUSS
• The Howe truss Is the opposite of the Pratt truss. The diagonal members
face in the opposite direction and handle compressive forces.
Matsuo Bridge Company - http://www.matsuo-bridge.co.jp/english/bridges/basics/truss.shtm
Competition Resources
• Bridges – a very comprehensive site
(http://www.teachers.ash.org.au/jmresources/str
uctures/bridges.html)
• Building Big - Bridges
(http://www.pbs.org/wgbh/buildingbig/bridge/in
dex.html )
• Westpoint Bridge Designer Software
(http://bridgecontest.usma.edu/ )
• Johns Hopkins Bridge Designer
(http://www.jhu.edu/virtlab/bridge/truss.htm)