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2008 News Releases



Seniors cap their undergrad engineering education by designing portable bridges

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By Debbie Levey
Civil & Environmental Engineering

People living in savanna climates can easily cross the small shallow streams that exist for most of the year. However, during the rainy season, these streams swell and create impassable barriers. As part of the senior capstone course, 1.103 Civil and Environmental Engineering Design, Professor Herbert Einstein asked students to design and build strong, light bridges that could be brought out during such floods.

The Class of 2008 was the first to participate in the revised engineering design course that now combines concepts from the environmental engineering science (1E) and civil engineering (1C) curricula and is a requirement for all CEE majors. “It worked out very well,” said Einstein. “Everyone worked in mixed teams of civil and environmental students.”

The rules specified a bridge 10 feet long and two feet wide, constructed with hand tools using common materials such as wood or wire. It had to be able to hold a ton of concrete blocks without sagging more than a half-inch, yet be light enough for a few people to carry, or simple enough to be quickly assembled on location. In addition, it should be attractive, and built on time and on budget.

Having watched students build bridges every year since spring 2000, Einstein remarked, “It’s amazing how the bridges are always different.” This year’s most unusual bridge folded up into a five-sided wheel shape, while another was collapsible like an accordion. A triangular truss, a hanging bridge with a chain underneath the bridge carrying the load, and a suspension bridge each had many unique aspects. Einstein praised the 1E students for contributing as much as the 1C students to the design and fabrication.

Occasionally a bridge cracks or slumps under the required load of concrete.  “Usually a bridge fails at the connections, which are very hard to design,” said Einstein. “This in itself is an important learning experience.”

Along with the bridge-building project, students in the new joint 1C and 1E design class collaborated on other projects with civil and environmental components.

“The capstone project puts together everything they have learned in the last three and a half years,” said Einstein. Two teams worked on the fabrication and distribution of home water filters in Ghana, where most people lack access to clean water. Another three teams proposed plans for reconstructing the MIT sailing pavilion with a minimum energy footprint through the use of solar and wind power.

Earlier in the semester, students collaborated on building hands-on models to teach physics and engineering concepts to a visiting high school class. One demonstration showed students how dams gained or lost strength with different shapes. After a quick blackboard review of formulas, students hooked up hoses to a tank with an earthen dam, and graphically proved the truth of the theoretical results.

Einstein co-taught the class with senior lecturer Pete Shanahan, technical instructor Steven Rudolph, and visiting lecturers Lisa O’Donnell, a consulting engineer, and Bashar Altabba, a bridge designer.

Wheel Bridge

Accordian Truss Bridge

Suspension Bridge

Delta (triangular) Truss Bridge

Hanging Bridge

Wheel Bridge