Abstract
This is a demonstration to the class on how shear walls and moment frames can be used to stabilize buildings subject to lateral loads.
Learning Objectives
After this activity, students should be able to:
- Explain how a shear wall works to stabilize buildings
- Explain how moment frames work to stabilize buildings
- Predict whether or not a building will resist lateral loads based on its lateral resisting system
Background
Wind and earthquakes create lateral loads on buildings that need to be resisted. Two ways in which these loads can be resisted is through the use of shear walls and moment frames. This demo provides visual examples of how these methods work to stabilize structures subject to lateral loads.
In this activity, a building frame is constructed using popsicle sticks connected using paper fasteners.
First, show that a building without any lateral load resisting system will fail subject to wind or earthquake.
Shear walls can be built in concrete or steel (typically concrete) and typically surround the core of the building, which is where the elevators and stairs typically are. The shear walls help resist the effects of wind and earthquake by providing a lateral resistance that is not provided by a frame where the members are pinned together. In this activity, a shear well can be implemented with a square of cardboard attached to the frame.
Another way to resist lateral loads is to make the connections in the structural frame rigid. By creating moment connections, the spots where the beams and columns come together are kept at 90 degrees. This provides rigidity to the building, creating a resistance to the lateral loads. These connections can be just on one bay (on each floor), so one floor’s moment connections can be removed to show that that floor will collapse with no lateral resisting system, even though the other floors stayed rigid.
Finally, a braced frame can be explained. One can use rubber bands for diagonal elements that can resist lateral loads as well. Pictures showing the braces in different portions of the building can be used to have the students predict which is stable and which is not, furthering their understanding. They should understand that every floor needs at least one system to prevent the floor from collapse under lateral / shear loads.
Materials List
Building
- 21 popsicle sticks
- Wooden 2x4 at least the length of 3 popsicle sticks
- Round head paper fasteners
Shear Wall
- Thick cardstock, with a width of one popsicle stick and a height of 3 popsicle sticks.
Moment Frame
- Binder clips
References
- Building Strength Demo (IRIS Earthquake Science). Robert Butler. Video accessible at https://www.youtube.com/watch?v=tPvkfzevJ-Q
- Build a Better Wall (IRIS Earthquake Science). Robert Butler. Materials accessible at https://www.iris.edu/hq/inclass/demo/build_a_better_wall
- Build a Better Wall: Parts & Construction (IRIS Earthquake Science). Robert Butler. Materials accessible at https://www.iris.edu/hq/inclass/video/build_a_better_wall_1_parts__construction
From the lecture: Fazlur Khan and Concrete Buildings