TEACHING CLUES AND CUES
This activity is designed
as a demonstration or as
a group activity. If you
decide to have each
group build a model wall you will
need more materials.
Encourage students to
choose roles within their
SETs and later report
their results by role, with
the technician reporting the data, the
engineer describing the calculations,
the scientist explaining the
relationships, and the coordinator
facilitating.
Students may try both
pushing the structure
directly and moving the
table. Shaking the table
a. Instruct one student in each group to push at the bottom of the
model from the lower right or left side. (When pushed just fast
enough, the model should collapse at the first floor only.) Ask students
why the other floors didn’t collapse. (The first floor collapsed because
it was too weak to transfer enough horizontal force to move the upper
stories. It could not transfer the shaking to the upper stories.)
b. Direct students’ attention to the load path diagrams on Master 4.2b
and explain that pushing the base of the building is equivalent to
applying force horizontally to the upper stories. A force applied
horizontally to any floor of a building is called the shear force on that
floor. Shear forces can be caused by the ground shaking of an
earthquake as well as by high winds. Invite students to carefully apply
horizontal forces at different points on the model to simulate
earthquake shaking. (Earthquakes affect buildings at ground level.)
4. Ask students how they could add structural elements to create a
path for the load to follow to the ground when strong forces act upon
the structure. Help the students discover the effect of adding a shear
wall, diagonal bracing, and rigid connections, using string, cardboard,
extra wood, and clamps, as in the diagrams on the master. On each of
the three diagrams provided, have students draw a force arrow (a
vector) and trace the path the force takes to the ground.
5. Challenge students to design and build three different arrangements
of the six structural elements depicted on the worksheet. Each time
they modify the design they must modify the diagram to show the new
load path. Check each structure and diagram until you are sure that
students understand the concepts. When a structure is well reinforced,
you should be able to push on the upper story and slide the whole
structure without any of the walls failing.
6. Either have the groups discuss the questions on the master, with one
student recording each group’s response, or ask individual students to
write responses to specific questions. After all the groups finish the
questions, have a reporter for each SET present its response to one of
the questions. Allow the class to come to some consensus on their
responses to that question, then proceed to another group until all the
questions have been discussed.
C. Conclusion
As a closing activity, challenge a volunteer to remove an element (a
craft stick) that, according to the load path diagram, is not carrying
any load. Have the student unbolt one end of that element and push the
reinforced structure to see if it holds. It will, if the load path is correct.
Finally, help the students connect the behavior of their model walls to
their mental images of real buildings during an earthquake. Emphasize
that the back and forth, horizontal component (or shearing) of ground
shaking is the force most damaging to buildings. Buildings are
primarily designed to carry the downward pull of
on which the structure rests would
simulate the transfer of energy from
the ground to the building.
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