This is a demonstration in class so that students understand the concept of buckling and how a shorter column can take significantly more compressive load than a taller column.
After this activity, students should be able to:
- Predict which column can hold more load, given identical columns of varying lengths
- Demonstrate a qualitative understanding of how length affects buckling
Important to the design of steel buildings is the concept of buckling. Because steel is so strong, not much material is typically needed. However, buckling can become an issue when steel is in compression.
In this activity, two 1/2” diameter sections of Schedule 40 PVC pipes are used to demonstrate the principles of buckling. One pipe should be approximately twice the length of the other (e.g. 30” and 60” length). First, show the students the two pipes and ask them to consider which will carry more load before buckling. Then, demonstrate the varying strength by pushing down on both, showing that the taller pipe is easy to bend while the shorter is significantly more difficult. It may be helpful to then show the equation for Euler Buckling, showing that the shorter pipe carries 4x the amount of load before buckling, which is why it was so much harder to buckle.
You can make this activity more quantitative by using a luggage scale to measure the amount of force required to cause the pipes to buckle, and attempt to match the measurements to predictions based on Euler’s buckling formula. See the paper referenced below for further details on this extension.
- PVC pipe, cut to two sizes, one twice the size of the other (suggestion: 2 feet and 4 feet)
Active Learning Demonstrations in Engineering Mechanics, Mark Diller. Proceedings of the 2016 ASEE North Central Section Conference. (2016)
From the lecture: Baker, Khan and the SOM Tradition of Structural Art in Buildings