retug October 03, 2022

One Way Load Distribution In ETABs

I have used ETABs one way load distribution button for a long time and it works great on flat floors and "slightly sloped roof" to distribute load based on tributary area.

Today though, a coworker of mine noticed on a slightly more pitched roof, angle of about 30 degrees, the one way loading was not working as intended (could not see applied loading due to tributary area).

I built a test model to explore the odd behavior.

Slab section properties uses one way distribution:

(3) sample floors are made, each with the same load and beam restraint layout, but you can see, once the floor becomes "too sloped", the load distribution switches from a line load on the frame elements to merely point loads applied at the edge of the membrane

 

The magic slope where this seems to occur is about 20 degrees from horizontal. 

Edit 2024-10-22

It appears that this 20 degree number is in the Set Tolerances button of ETABs, tweak away.



Hopefully this post saves someone in the future the pains of troubleshooting this odd behavior

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  • Latest Comments
  • retug on Transfer Diaphragm Design -

    @316Jq, The way I understand, the diaphragm design force (inertia force) per 12.10.1.1 is the inertia force.

    Using the blog example numbers let's say this is 1392 kips.

    The transfer diaphragm force could be estimated to be the delta in shears above and below the transfer level ~ (1500 -  …

  • 316Jq on Transfer Diaphragm Design -

    Just wonder how do you separate inertia force and the transfer force? The inertia force might be controlled by the Fpx,min per ASCE12.10-2,  while the transfer force might need to be multiplied by rho or omega. This is also briefly discussed in NHERP design guidance you used. 

  • retug on Section Cutter - ETABs Plugin -

    Hi Rodrigio, thanks for reaching out.

    My email is retug.austin@gmail.com, feel free to shoot me an email.

    The section cutter tool needs a bit of updating to work with the newer version of ETABs, but happy to discuss what you might have in mind for the add-in.

    Thanks