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

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

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

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 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 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 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 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 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 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