INTRO TO CIVIL ENGINEERING: BRIDGE PROJECT
The goal of this project is to work in TEAMS to design and build an optimal 2-lane roadway bridge.
The “optimal” bridge will be judged on three criteria:
60% satisfies minimum criteria (span length, deck width, vertical clearance, weight supported)
20% simplicity of design and construction (number of materials used, construction methods)
20% lowest amount of bridge deflection under a maximum static load
Good information on bridge types can be found on the web at: www.pbs.org/wgbh/nova/bridge
Another good bridge design site is: http://ftp.usma.edu/cme/outreach/WPBD/wpbdhome.htm
Each group (~4 people) will be given the following materials to build a bridge:
1. 10 straws 3. 10 5” skewers 5. 10 pins
2. cardboard 4. 4 ft of string
You may additionally use Scotch tape (dimensions; no more than 12 inches; I’ll bring a roll to class).
You may cut or bend all of the items in any way you choose. No other tape or glue is allowed to hold
your structure together. Bridges must use standard bricks (7.5” long x 2.25” tall x 3.5” wide) at the
ends for support (2 maximum at each end).
The bridge should be designed for a minimum of “two lanes” of width, “free” spanning a distance
between major end supports (the bricks) of 120 ft (no intermediate supports to desk within the 120’).
Assume that your bridges are being scaled at a 1:100 ratio. (1 of yours = 100 real)
The bridge must hold a minimum of 2.25 lbs with less than 0.25” deflection at any point.
Your group should prepare a 3 to 6 page justification of your bridge design. You should include the
way you converted from the design specifications (above) to the scaled lengths. You should include
types of designs considered, but not selected for your final design. (I recommend that each person
should brain-storm a bridge design on their own, and then your group should get together and select a
single option. A sketch or description of the alternatives and why they were selected or not should be
included in your group write-up). You should include a list of all the materials that you used in your
bridge. The “scale” of the final bridge should be evident in the write-up. Discuss issues related to the
construction of the bridge from the provided materials (length of time, difficulty). Decide how you
want the bridge to “interface” with the bricks on the end. Leave space to write in the load and
deflection information we generate in class. Justification due in class on Oct. 9.
Your group can either construct your bridge in advance, or construct it in class. However, in order to
leave time for load-testing the bridges, all bridges should be ready for load testing no later than 2:45
pm. Your team will have a maximum of 3 min. to “attach” your bridge to the end supports. Load
testing will be conducted by adding weight at the center of your bridge, and measuring deflection.
“Failure” occurs when the bridge collapses under the load. This includes failure by torque of the
structure dumping off the weights, the ends of the bridge coming off of the supports, and any portion of
your bridge touching the table.
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Good reference material on design standards can be found on the California Department of Transportation web-site, which
links to their highway design manual on-line: www.dot.ca.gov/hq/oppd/hdm/hdmtoc.htm
Excerpts from this document include:
(1) State Highways. The clear width of all bridges shall equal the full width of the traveled way and paved shoulders on the
approaches with the following 2 exceptions: (a) Bridges constructed as replacements on existing 2-lane, 2-way roads shall
not have 1.2 m.
Vertical Clearances of Major Structures.
Freeways and Expressways -- 5.1 m shall be the minimum over all portions of the State facility for new construction
and 4.9 m minimum for overlay projects
Conventional Highways and Local Facilities, All Projects -- 4.6 m shall be the minimum over the traveled way.
Other information: old roadways used to have a 13 ft standard lane width, while newer roads have a 15 ft standard lane
width.