Frames and connections
Portal Frame Deflection: Why Restraint Matters
Justice pushes an isolated portal frame, then adds restraint and compares how the model moves. The demonstration also points out lateral-torsional movement at a compression flange.
Justice pushes an isolated portal frame, then adds restraint and compares how the model moves. The demonstration also points out lateral-torsional movement at a compression flange.
Authored explanation · separate from narration
The concept behind the demonstration
Justice pushes an isolated portal frame, then adds restraint and compares how the model moves. The demonstration also points out lateral-torsional movement at a compression flange.
Keep the model in context
The observed shape and the narration describe this physical model. They are not a prediction of full-size deflection, a member-capacity check or an erection instruction. Real stability depends on the members, restraint and connections working together.
Read the transcript
Transcript checked against the recording.
As we look at this portal frame, what would be the deflected shape if I push right here?
As you'll notice, it doesn't have the textbook-defined deflected shape. That's because it has an in and out of plane instability. But if we add some stability by restraining it in and out of plane, we'll notice that that story changes. We can see the textbook deflected shape up here.
You'll also notice some lateral-torsional buckling in this compression flange.
Bring it into the conversation
Pause. Compare. Explain.
What changes in the model, and what stays the same?
The observed shape and the narration describe this physical model. They are not a prediction of full-size deflection, a member-capacity check or an erection instruction. Real stability depends on the members, restraint and connections working together.
A physical point of reference
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