moment-resisting column-to-rafter connections
Justice's post contrasts post-and-beam framing with moment-resisting column-to-rafter connections. It explains that a rigid frame's in-plane behavior can coexist with pinned-base assumptions.
Frames and connections
Rigid frame connections and pinned bases
Rigid-frame behavior depends on the intended connection behavior. A rigid frame can have idealized pinned bases.
Compare a pin-connected post-and-beam model with added X-bracing, then look at a separate rigid frame. The movement makes the distinction between in-plane resistance and out-of-plane restraint visible.
Authored explanation · separate from narration
The concept behind the demonstration
The word “rigid” does not mean every part of a frame is fixed against rotation in every direction. A connection's intended behavior is part of the structural model.
where rotation is permitted
Use the physical model to discuss where rotation is permitted and where moment is transferred. In-plane frame action does not settle out-of-plane stability or determine the actual stiffness of a particular joint.
Keep the model in context
This is a qualitative hand demonstration of the model shown. It does not measure full-size stiffness or establish a safe erection sequence. Real members, connections and restraints must be designed as a complete system.
Read the transcript
Transcript checked against the recording.
We'll see how we typically model things as engineers, so post and beam is modeled as a pin-pin connection. You can see it's got a lot of wobble, zero resistance.
But then, once you put in the X-bracing, everything stiffens up a lot. You can bend in the out-of-plane, but not in-plane. To show the same thing, you can see here, we push here and it deflects without the secondary.
But it has resistance.
Bring it into the conversation
Pause. Compare. Explain.
Which joint assumption changes the way the columns and rafter work together?
The model does not classify a real joint's restraint or certify connection performance.
A physical point of reference
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