This is an in-class kinesthetic activity where students investigate how tall structures with a wide base (like the Eiffel Tower) versus a narrow base (like the Washington Monument) resist lateral forces. Through experiencing the differences physically, the students can understand the effects wind loads have on structures and their shapes.
After this activity, students should be able to demonstrate that:
- Wind loading on structures causes overturning moments
- The Eiffel Tower’s shape was designed specifically to counter the moment created from wind
- Gravity and wind loads act together and influence how a building is designed
- (More advanced) A structure that mirrors its moment diagram results in an efficient form
The Washington Monument, constructed of heavy masonry, is dominated by gravity loads and thus can afford to have the narrow base that it has. The Eiffel Tower, on the other hand, is extremely light-weight and had to be designed with considerations for wind loads, which Gustave Eiffel did with extreme efficiency.
In taking account the bending moment generated by the wind loading on the Eiffel Tower, Eiffel came up with the efficient form that is today’s iconic structure.
In this activity, students can feel the difference that standing with a wider stance versus a narrow stance has in resisting a lateral force. This will help them correlate the form of the Washington Monument and the form of the Eiffel Tower with the loads that control them.
No building necessary. Have the students pair up. One student stands with their legs together and the other tries to gently push them over at shoulder level. Next, the standing student spreads their legs in a wider stance and the other tries to gently push them over once again. Have the students switch roles. They should have felt more stable and resistant to toppling when using a wider stance.
In this kinesthetic activity, the person applying the force represents the wind force and the person resisting the force represents the tower. By following the shape of the moment diagram for a wind-loaded vertical cantilever, Eiffel designed his tower in a way to resist lateral wind loads (i.e. the horizontal force of wind) while keeping the material use to a minimum. Students can intuitively relate the shape of the Eiffel tower to the ‘wide stance’ one adopts when attempting to resist an overturning force. An everyday example of this is the posture one adopts when standing in an accelerating subway car.
Finally, have the students summarize what they learnt from this activity with a question or discussion about the general conclusions. The responses to this question can be used to assess the learning objectives of this activity.
From the lecture: The Eiffel Tower and the Washington Monument