To: Richard Busick and Joe Grodeski
From: Group D (Section A, 1:30 PM); Joe Mullen, Sheng Lu, Javi Medina-Fetterman, Will
Sweeney, Alex Moen
Date: 10/22/2011
Subject: Bridge Building Memo
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Introduction
For the Bridge Design Competition lab, the main goal was to create an activity that
allowed our group to work as a team on a time-restricted project. Many inhibitors, especially
finding times when everyone in the group could meet, presented themselves during the course
of the project. The exercise itself also encapsulated the ability to apply scientific and
engineering knowledge to a rather practical construction problem. Multiple bridge theories
were hypothesized during the course of the lab, truly testing the rudimentary scientific and
engineering knowledge of our group. This memo contains the results of our group’s bridge
along with bridge design flaws that could have been improved. Also, this memo encompasses
multiple problems that our group encountered during the project itself along with a reflection
on our teams overall functionality together.
Results
The maximum load weight of the bridge was 32 lbs, and the bridges weight was 37 grams.
Discussion questions
1.
Our bridge appeared to have failed in the middle where it was weighted. Upon finishing
the build, the group was very uncertain of the amount of weight the bridge would hold,
however, after viewing other bridges that were tested we anticipated a failure point of
approximately forty pounds. The first obvious way our design could be improved would be to
make the bridge legal by competition rules which constituted a lamination of less than a
quarter inch. Another feature that I believe would be to have chosen a simpler bridge design
such a box rather than a segmented arch for the top support. This would have cut down on
weight and allowed for fewer points of failure. While building the bridge clothing pegs should
have been used to clamp segments together while drying and some pieces needed to be more
precisely measured. Since failure occurred in the middle of the base of the bridge (the main
horizontal structure where the weight is placed) more supports should have been placed there
using the materials that were used to build a supporting structure underneath the bridge which
were unnecessary. After performing this lab a lot of knowledge was acquired and higher
quality bridge would be built if this assignment were given again.
2.
Our group met three times in order to complete the bridge building process. No team
problems occurred during bridge building. To ensure the lab’s success the following steps were
taken:
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A unanimous agreement was made regarding the bridge’s design.
Construction was straightforward; each team member was assigned a part of the bridge
to build.
New ideas were discussed with the group
The meetings were organized into three categories—design, building, and refining.
Design
During the first meeting, the group designed the bridge. The design process involved
sketching, scaling, and adjusting problem areas. Upon reviewing multiple designs, the group
chose a bridge with a circular shaped truss that would use most of the balsa wood and carry a
decent load.
Building
The most extensive part of the lab was the building process. Upon completing the
design, the group began cutting and gluing together the primary structures of the bridge.
Perhaps the biggest problem encountered during the lab was the glue’s drying time; Pieces had
to stand still for at least thirty minutes before they could be moved. After one five-hour
meeting the bridge was complete—only a few refinements needed to be done.
Refining
The third meeting concluded the bridge building process. Gusset plating was added to
most of the joints, and main structural areas were strengthened with leftover wood. The whole
refinement process took no more than two hours, but greatly strengthened the bridge.
Overall, the team functioned well together. No disputes occurred, and the bridge was
built in a timely fashion. All team members contributed with interesting ideas, leading to a truly
unique bridge. Had the work not been properly organized, the bridge would have taken much
longer to build and team problems may have occurred.
Problems encountered
The hardest part of our bridge was the actually construction of the bridge. Because we
had to skip around a few different ideas for bridges, we had to adjust accordingly. For example
we looked up bridge designs on the internet and bridges with arc designs held enormous
amounts of weight. This became a problem because other groups were also trying this tactic
and they were having no luck successfully bending the wood because it was too fragile. So we
had changed our minds to a simplistic triangular bridge, and started to draw that concept. From
that concept we decided why not combine our ideas and make an arch bridge with segments of
wood. The challenge behind that was that it became difficult to make sure that the wood fit
into where it had to be, be not slanted, and also have the glue dry. This easily became our
biggest challenge, but because we took the time to stay for a while and work on the bridge as a
team it became easy. Possible changes to this lab would be to have some type of pre-cursor to
the actually lab to get a feel for what types of bridges hold better than others. All in all this lab
was a very fun, and good challenge and would be very fun to do again.