PyritePrinting
Load path and bracing layout
A roof-level force needs a route to a resisting line. Some stiffness in the model is different from an intentional, connected load path.
Compare a push at the eave with a push at the ridge. Watch the model with roof bracing absent, after the sidewall brace is removed, and after a roof diagonal is added. The point is the difference between a direct intended load path and the residual flexibility of the other members.
Authored explanation · separate from narration
This topic follows a force from the roof level toward the wall-bracing system and the base. It connects two ideas that can look separate on framing drawings: horizontal transfer and vertical resistance.
Justice's post compares loading at the eave and ridge while changing the model's roof and sidewall bracing. The unbraced-roof configuration still has some stiffness through its remaining members and connections; force does not simply stop moving.
The teaching question is whether the intended path is connected and what each part contributes. The model's response is not a substitute for determining the required strength and stiffness of the actual members, connections and supports.
This is a qualitative model demonstration, not a measured stiffness test or a full-size building design. “No load path” in the simplified demonstration means no clear intended braced path in the direction discussed; it does not mean every remaining member has literally zero stiffness. The closing explanation preserves that distinction.
Transcript checked against the recording.
I'm going to show a few examples of load path. If I apply a load here on the building, how does it get to the ground? We can see it's going to go through my eave struts, come down through this X-bracing, and then it hits the foundation.
But if I push here, how does the load get out? You can pause the video and take a guess.
Here is what it looks like. Without any roof bracing, the load still makes it to the ground, but it's traveling through the weak axis of all these beams. The struts, or the roof purlins, strut the load down the line and make it to the resisting system. We can prove that by removing the X-bracing. You can clearly see that now there is no load path. Even though the load path before was through the weak axis of the beams, it still had a load path.
We're just deflecting at the ridge. For example, if we go in and add our roof bracing, we'll be able to see how this works. We can see that our load is going through our purlin, engages this X-brace, which pulls here. As it pulls, it then travels down this eave strut and to the ground. That's not 100% true, as we're still pulling load through the weak axis, but that is the direct load path.
Bring it into the conversation
What connects the ridge-level force to the braced line in the described model?
The demonstration does not evaluate cladding, every diaphragm effect, foundations or real-building capacity.
A physical point of reference
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