Transcript Slide 1

Designing and Building
File-Folder Bridges as an
Introduction to Engineering
The Waddell A-Truss Bridge
COL Stephen Ressler, P.E., Ph.D.
Department of Civil & Mechanical Engineering
U.S. Military Academy, West Point
Why File Folders?
 Inexpensive.
 Easy
to cut, bend, and glue.
 Surprisingly predictable structural
behavior.
 Can be used to build:
Tubes and bars.
 Connections that are stronger than the
attached structural members.

Let’s build this bridge...
Waddel “A Truss” Bridge over Lin Branch Creek
Trimble, MO
http://structurae.net/structures/data/index.cfm?id=s0001386
The Design
 Design
Requirements:
Span–30 cm
 Loading–5 kg
(at midspan)

10 mm x 10 mm Tube
Doubled 4 mm Bar
Doubled 2 mm Bar
Profile View
Our A-Truss Bridge
Materials & Equipment
 File
folders
 Yellow carpenter’s glue
 Building board (Styrofoam or cork)
 Pins
 Scissors
 Ruler
 Drawings – side and top view
Prefabrication of Members
Cut out bars
 Cut out and assemble tubes
 Cut out gusset plates
 Trim bars and tubes to length

Gluing Flap
Rubber Cement
Part 1 - Prefabrication
10mm X 10mm Columns
 Prefab Double 4 mm Bars
 Prefab Double 2mm Bars
 Prefab Gusset Plates – 3 styles
 Prefab Middle Beam
 Prefab
Part 2 – Truss Construction
Trim Bars and Tubes to Length
Bottom Chords
(2 per team)
Trim Bars and Tubes to Length
Bottom Chords
(2 per team)
Trim Bars and Tubes to Length
Verticals
(2 per team)
Trim Bars and Tubes to Length
Verticals
(2 per team)
Trim Bars and Tubes to Length
End Posts
(2 per team)
Trim Bars and Tubes to Length
End Posts
(2 per team)
Set up the Building Board
Each Team Member:
 Place the layout drawing on your building board.
Set up the Building Board

Place a sheet of plastic wrap over the layout drawing.
Add Gusset Plates
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Place Gusset Plate A at its correct location on the layout
drawings.
Hold it in place with two pins.
Add Gusset Plates

Repeat the process for Gusset Plates B, C, and D.
Add Bars

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Apply a line of glue along the bottom edge of Gusset Plates
A, B, and C.
Place a 2 mm bar in position as the bottom chord AC.
Stretch tight and hold in place with two pins.
Add Bars
Apply glue to Gusset Plates B and D.
 Place a 4 mm bar in position as the vertical member BD.
 Stretch tight and hold in place with your fingers.
Each team should now have two of these subassemblies —
the lower half and the upper half of one truss.

Add Tubes
For the bottom half of the truss (one per team):
 Apply glue to Gusset Plates A and D.
 Place a 10mm x 10mm
tube in position as end post AD.
 Hold in place for a
minute until the glue sets.
Add Tubes

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Apply glue to Gusset Plates C and D.
Place a 10 mm x 10 mm tube in position as end post AD.
Hold in place for a
minute until the glue sets.
Add Tubes

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Cut a 2 cm length of 10 mm x 10 mm tube.
Apply glue to Gusset Plate B.
Place the tube vertically on the gusset plate.
Hold in place for a minute until the glue sets.
The Finished Half-Truss

Allow all glue joints to dry.
Assemble the Two Halves
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Pull out all of the pins on both halves of the truss.
Carefully separate the upper half of the truss from the plastic
wrap.
Keep the lower half of the truss on the building board.
Assemble the Two Halves
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Put glue on the tubes at A, B, C, and D.
Place the upper half
onto the lower half.
Stretch the bars tight
and hold until the glue has set.
Assemble the Two Halves

Allow all glue joints on the completed truss to dry.
Finish the Truss

Trim off the excess length on both
bottom chords (AC) .
Place the Structure into Service
The completed bridge
Load test with 5 kg of sand
suspended from midspan