Student Activities Student Projects

Design and Construction of a Timber Bridge : National Timber Bridge Design Competition

Students: Charles Bado, Kevin Donahue, Ted Forgit, Tom Krajewski, Anna Novey, Matt Peterson, Chris Phelps
Faculty Sponsor: Peggi Clouston, BMATWT, NRC
Project Type: Independent Study
Year: 2003

Introduction:
The purpose of this project was to conceptually design, construct and non-destructively test a full-size pedestrian timber bridge. The guidelines for construction are those set out by the National Timber Bridge Design Competition which is an annual event sponsored by the United States Department of Agriculture (USDA) and the United States Forest Products Service.

The competition is open to universities across the US and Canada for student chapters of the American Society of Civil Engineering (ASCE) as well as the Forest Products Society (FPS).

Aim of Project :
The aim of the project was to construct a fully functional bridge (treated to AWPA standards for "above ground use") which has:

• Minimal overall bridge deflection
• Minimal deck deflection
• Minimal weight
• A maximum of 25% non-wood content by weight

The bridge was designed and built with the intent that it would be used in a local trail or park after completion of the testing. As a Drafter in the Engineered Wood Department

Method and Research :
The project entailed 6 definitive stages:

• Conceptual design stage. This was the creative phase. Many resources were tapped to accumulate ideas on how the bridge should look. The list was narrowed down to three basic profiles and based on their pros and cons (and our constraints: time, money and facilities), we choose our final design.
• Structural design stage. The material and size of the components were determined
• Purchase and receiving materials stage. Most materials (lumber and nails) were graciously donated by Cowls Building Supplies. Other incidentals were purchased with a modest budget of $700.
• Construction stage. Bridge components were prepared and assembled with the invaluable help of Mr. Dan Pepin from the department of Natural Resources Conservation.
• Testing stage. The bridge was tested nondestructively with concrete block weights arranged in accordance with the National competition loading scheme.
• Report writing stage. All stages of the project were compiled and edited in scientific report format.

Results :
The bridge performed extremely well. The maximum deflection of the entire bridge (after 1 hour of loading) was a mere 0.72 mm. The design competition allowed a maximum of 10 mm deflection. The maximum net deck deflection was 2.7 mm.

An unbalanced load condition was also tested whereby
the 20kN load was placed as close as possible to one
main support beam. During this test, the maximum
deflection was found to be 2.92mm. This is well within
an acceptable working range for a pedestrian bridge.

The bridge project was a tremendous success. We
learned how to manage a real construction project
from beginning to end. The bridge is currently being
used as a trail bridge by the Amherst Conservation
Commission.

Acknowledgements :
We would like to thank Cowls building supplies for donating the lumber for this project. We also owe our gratitude to Mr. Dan Pepin and Dr. Peggi Clouston for spending many hours helping us design and fabricate the bridge.