DESIGN AND CONSTRUCTION OF A MODEL BRIDGE Regulations and

							             DESIGN AND CONSTRUCTION OF A MODEL BRIDGE
                                   Regulations and Specifications
General

The objective of this project is to design and construct a bridge that has the maximum structural efficiency.
Each student is to design and construct his/her own bridge model using wooden paddle sticks and PVA glue.
Your bridge model is to be of the under-slung truss type as depicted in the figure on the next page. The bridge
depicted in the figure is intended to be purely diagrammatic. You are at liberty to use any bridge shape with any
number of members, provided that the resultant model falls within the dimensional parameters outlined in the
figure.

Judging/Testing

If your model bridge does not comply with the required geometric and dimensional parameters, it will be
ineligible for testing. Judging of your model will be accomplished by test loading it to failure. Your model will
be supported as depicted in the figure and the load will be applied at mid-span. The loading beam (contact
member) will extend over the width of the model. Both the load and mid-span vertical displacement will be
monitored.

Strength/Performance Rating

Performance will be judged by determining your model’s strength-to-weight ratio. This will be accomplished by
calculating the maximum load at failure and dividing it by the mass of the model. Therefore, the bridge model
that reaches the highest gross loading will not necessarily be the best design. It is up to each student to decide
on the optimum balance between mass and strength.

Bridge failure will be determined by two criteria. A bridge shall be deemed to have failed when it can no longer
support an increase in load and/or its displacement exceeds 30 mm.

Detailed Specifications

   1. Building materials are to consist solely of standard wooden paddle sticks and PVA glue.
   2. Sticks may be cut and/or glued to form any shape. No other materials may be used, e.g. other timber,
      metal pins, wire, super glue etc.
   3. The total mass of the complete bridge is not to exceed 275 grams. Note than each stick weighs
      approximately one gram.
   4. The bridge must span between the ends of the testing frame which has a clear distance of 500 mm.
   5. The designer should assume that the bridge is free to rotate at the supports and expand/contract during
      loading.
   6. The bearing length at each support shall be between 20 mm and 25 mm so that the maximum overall
      bridge length must be more than 540 mm and less than 550 mm.
   7. No part of the bridge may project more than 20 mm above or 110 mm below the bearings.
   8. The maximum width of the bridge is not to exceed 110 mm.
   9. The only contact between the bridge and the testing frame, throughout the testing, shall be on top of the
      supports at the bearings and at the mid-span loading beam.
   10. The top of the bridge need not be covered to simulate a road surface.
Where to Get the Materials?

You can buy the paddle sticks and Selleys PVA Woodworking Glue from Bunnings, Safeway or craft shops.
Each bridge model will require around 100 to 300 sticks, depending on your design. A bottle of 100 ml PVA
glue will be sufficient to build one model. The total cost for the paddle sticks and PVA glue is around $10.

Your Goals

To receive a PASS mark for this project, the strength-to-mass ratio of your model must be greater than 250. For
example, if your model weighs 200 grams, you should aim to have your bridge to carry more than 50 kg of load
(strength to mass ratio: 50kg /0.2kg = 250).

To be competitive at the national level in Australia, the strength-to-mass ratio needs to reach 2000. Any student
who can exceed 2000 will receive bonus marks in additional to full marks for this project.




Acknowledgement

This document has been adapted from the national Paddle Pop bridge competition regulations and specifications
which are gratefully acknowledged.