1. The Waddell A-Truss Bridge
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

2. 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.

3. Let’s build this bridge...
Waddel “A Truss” Bridge over Lin Branch Creek Trimble, MO

4. 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

5. Our A-Truss Bridge

6. Materials & Equipment File folders Yellow carpenter’s glue
Building board (Styrofoam or cork)
Pins
Scissors
Ruler
Drawings – side and top view

7. Prefabrication of Members
Cut out bars
Cut out and assemble tubes
Cut out gusset plates
Trim bars and tubes to length

8. Part 1 - Prefabrication Prefab 10mm X 10mm Columns
Prefab Double 4 mm Bars
Prefab Double 2mm Bars
Prefab Gusset Plates – 3 styles
Prefab Middle Beam

9. Part 2 – Truss Construction

10. Trim Bars and Tubes to Length
Bottom Chords (2 per team)

11. Trim Bars and Tubes to Length
Bottom Chords
(2 per team)

12. Trim Bars and Tubes to Length
Verticals
(2 per team)

13. Trim Bars and Tubes to Length
Verticals
(2 per team)

14. Trim Bars and Tubes to Length
End Posts
(2 per team)

15. Trim Bars and Tubes to Length
End Posts
(2 per team)

16. Set up the Building Board
Each Team Member:
Place the layout drawing on your building board.

17. Set up the Building Board
Place a sheet of plastic wrap over the layout drawing.

18. Add Gusset Plates
Place Gusset Plate A at its correct location on the layout drawings.
Hold it in place with two pins.

19. Add Gusset Plates
Repeat the process for Gusset Plates B, C, and D.

20. Add Bars
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.

21. 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.

22. 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.

23. Add Tubes 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.

24. Add Tubes 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.

25. The Finished Half-Truss
Allow all glue joints to dry.

26. Assemble the Two Halves
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.

27. Assemble the Two Halves
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.

28. Assemble the Two Halves
Allow all glue joints on the completed truss to dry.

29. Finish the Truss
Trim off the excess length on both bottom chords (AC) .

30. Place the Structure into Service
The completed bridge
Load test with 5 kg of sand
suspended from midspan