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Story Drift Results do not Match Joint Deflections

Story Drift Results do not Match Joint Deflections

Story Drift Results do not Match Joint Deflections

(OP)
Could there be any reason that the story drift results would not match joint deflections? I have a case where I define a node as a story, and compare the story drift results to the same node joint deflections. The story drift does not contain a Y-drift (Y is vertical), but the joint deflections do contain Y deflections. Any ideas? I attached a screen shot for reference.

RE: Story Drift Results do not Match Joint Deflections

In the current RISA, you define story joint for each direction. In your case, you have defined an X direction story joint, but not a Y direction story joint. That's why you're only getting the story drift reported for the one direction.

RE: Story Drift Results do not Match Joint Deflections

Sorry, I didn't look closely enough at your first image.

There is no Y direction drift because Y is your vertical axis. But, you are getting X and Z direction drift, right? And, the X and Z direction drift does match your X and Z joint deflections.

RE: Story Drift Results do not Match Joint Deflections

(OP)
JoshP, correct, Y is the vertical direction. I guess it makes sense that you don't have "story drift" in the vertical direction. However, on a separate model (see attached) (again Y is vertical), I only have Y drift? Is it something internal to the program?

RE: Story Drift Results do not Match Joint Deflections

I don't have an explanation for that. It doesn't seem correct to me, but I'd have to see the model to know for sure.

Also, what version of the program are you running? There may be an old bug that I don't remember. If I know the version I could look at the release notes for subsequent releases to see if there was anything corrected that sounds similar to what you're seeing.

RE: Story Drift Results do not Match Joint Deflections

Ahhhh, that makes more sense now. Though I had to scratch my head for a while before it started making sense....

Story 1 is at a 0 ft elevation. Since there is no Story 0 defined, story 0 will be assumed to also be at a 0 ft elevation! And, story drift calculations blow up (divide by zero errors). Hence the program refuses to do the calculation.

Try instead to define joint N12 (which is at -5 ft elevation) as your story 0. Then you should start to get drift results.

Apparently I was wrong about the Y drift not being reported when the Y axis is vertical. It will still be reported based on the "height" difference in the Z direction. Though I would not personally use this for anything as it is not a true drift.

RE: Story Drift Results do not Match Joint Deflections

(OP)
Yes, that does make sense now. I guess to close out the thread, I would want to make sure that my story 1 node never has a y = 0 coordinate. Thanks for you help JoshP

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