The Big Bridge Design Contest

Description

You will design and build a bridge constructed from balsa wood according to the contest rules listed below.  A competition will be held on Nov. 10 during which the bridges will be tested and judged according to the criteria listed below.  Your grade for this part of the course (20% of the total course grade) will be determined by the performance of your bridge.

Contest Rules

You will construct your bridge from the following cross sectional sizes of balsa wood: 1/16”, 3/32”, 1/8”, 3/16” and 1/4” square.  The joints connecting these balsa members will be made with a hot glue gun.  Glue may only be applied at the joints.  Do not use glue as a structural member of your bridge.

The bridge shall be free-standing (not attached to the loading stand in any way), and must span a distance greater than 1.0 m between two level surfaces, which are 1.0 m apart. Support for the bridge shall be from the top of the level surfaces, and their edges may not be used for support in any way.

The mass (weight) of the bridge shall not exceed 750 grams including the loading platform and U-bolt.

The maximum vertical depth, from the highest to the lowest point in the structure, shall not exceed 0.5 m.

The bridge must include a decking of balsa to provide a suitable road surface at least 50.0 mm wide across the full span of the bridge.

The following three conditions must be met:

An official “loading platform” made of 1/4 inch fibreboard with a metal hook attached, must be obtained from Dr. Yuly.  The loading platform must be located at the center of the bridge, at the same level as the bridge deck. The loading platform cannot be altered in any way.

Any bridge structure below the loading platform shall not exceed a depth of 5 cm.

To provide for attaching loads to the bridge, a loading platform must be part of the structure. The only contact between the load and the bridge shall be at the U-bolt. To facilitate attaching the loads to the bridge, there must be clear area around the loading U-bolt of approximately 4 cm x 4 cm square.

All bridges will be weighed. No work can be done on the bridge in the competition area, but a repair area will be provided in the vicinity. Any bridge that is worked on must be re-weighed before the competition. No repairs or modification will be allowed after the competition begins. All bridges will be inspected to insure that all contestants have met with the bridge building rules. Non-complying bridges will be disqualified at this point.

All bridges will be placed on two level, smooth topped platforms with an open space of 1.0 m between them. The owner of a bridge will be responsible for positioning of the bridge and removal after testing in a reasonable amount of time.

The magnitude of the load for each cycle of loading will be established by the judges. The loading shall be for a ten second period as determined by an official timekeeper. Bridges may not be touched while loaded.

The maximum load my be considered to have been reached when displacement of the bridge deck reaches 1/2 inch, or when the bridge fails, at the choice of the bridge owner.

Judging Criteria

The following scheme will be used to determine the points awarded (subjectively by Dr. Yuly) for your bridge design.

1.      Bridge Assignments (20%) – The initial bridge assignments will be worth the following:

Handout #1 Questions 1 & 2 2%
Calculate forces in simple truss by hand 5%
Use visual analysis to model simple truss 5%
Structural strength plots for balsa wood 5%
Construct simple truss bridge 3%

2.      Aesthetic Qualities (20%) – Completely subjective rating based on the feelings of the judging panel.

3.      Economics (20%) – How economical is this design?   A total cost will be awarded for the bridge design as follows:

a.       Materials cost – the cost of all the raw materials used in your bridge design.  This is calculated by (1) determining the total mass of the bridge, and (2) multiplying by $1 for each gram .

b.      Connection cost – this accounts for the labor costs associated with your bridge design.  It will be calculated by (1) determining the total number of joints in your bridge and (2) multiplying by $1 for each joint.

4.      Accuracy of predictions (20%) – before your bridge is tested, you will be required to disclose your predications for (1) the total weight that your bridge will support before breaking, and (2) where you predict it will break.

5.      Brute Strength (20%) – ranked in order of total bridge strength.