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EDT Bridge Building Design Competition

The objective of this project was to design a bridge that is able to hold at least 20 pounds of weight with a high efficiency (efficiency = weight held in Lbs / Mass of bridge in Lbs x 0.22). To begin the project, we design the bridge using the West Bridge Point program. This program has a feature that allows us to examine where tensions lay the most in the bridge design. We design our bridge with the consideration of the weight of the materials we use for the construction. Thick basswoods, paper, and white glue are the main materials we use in the project. Thinner basswoods are use to construct bending features of the bridge. However, there are some main required specifications in this project: maximum mass of the bridge is 40 grams, the maximum width of the bridge is 4 inches and the minimum weight bridge must support is 20 pounds. The bridge is given an enough amount of time to design, revise and construct.

Problems Encountered:

There are many problems our team encountered during each phase of this project. During the first phase of designing, our team has no problem of using the West Bridge Point program to create the first draft of our bridge. However in the actual constructing progress, difficulties of measuring the specific length of basswoods according to the draft emerged. Cutting basswoods with an ordinary cutting knife decrease the chance of cutting a perfect basswood with the exact measurement. Also, connecting all the cut basswoods with white glue became difficult when all the measurements of basswoods are not exact. As a cause, we need to use cutting knife to reshape all basswoods to minimize the gaps between them. A stronger bond is then created when two exact basswoods are glue together. The last major problem our team encountered is the overweight of the bridge. The final mass is 41.1 grams while the maximum weight of the bridge should only be 40 grams. An increase of bridge mass will decrease the final efficiency of the bridge.

Bridge Revisions:

Many revisions are made during construction. Triangles are added between two intersecting basswoods to increase the strength of resisting the resulted tensions when weight is added. The base of the bridge was also revised. The pattern of basswoods on the base of the bridge was constructed in shape of triangles. When tensions cause the bridge to pull down, the base will ease the tensions.

Final Result:

Our testing result wasn't that great because our efficiency is low which is 2.78. Calculate by the equation: weight held in lbs/ mass of bridge in lbs (25.1/ 41.1 x 0.22). However, our bridge broke after a few weight added to it because we did not glue the top part of the bridge strong enough. Also because of the incorrect length of the basswoods, we tried to add small pieces of basswood onto the shorter basswood which it decreased the strength of the bridge but increase the chance of breaking the bridge. Moreover, because our bridge is overweight (41.1lbs) so it decreases the efficiency since more heavy the bridge is, the lower the efficiency is. While on the other hand, the lighter the bridge is, the more efficient it would be since it is the efficiency of the structure that is being judged and not the load that the bridge can carry.

Construction:

Materials

basswood, paper, and white glue. Evidence of other materials will disqualify an entrant

Bridge Mass

Maximum mass of bridge is 40 grams. Included in total mass are adhesive/glue, basswood and paper.

Construction Forms

Any construction form is acceptable within the parameters set forth in these specifications. Basswood sticks may be cut, resized, and shaped. Paper and sticks may not be coated over .5” from the joint to improve strength.

Parameters - Each bridge must be built to the following parameters

1. The bridge must support a minimum of 20 pounds.

2. Accommodation must be made for a block, ¾” x 2 ¾” x 12” to pass through the centerline of the bridge, while resting on the two horizontal surfaces (support level) of the testing apparatus (to simulate a vehicle driving along the road bed of the span.)

3. Accommodation must be made for a ½” rod to pass through the bridge at the mid-span, across the centerline. The rod must be able to rest at, or up to .5” above the mid-span support level without interference from any structural element.