Effective Length Method

RE: Effective Length Method

Qing Zhong — Mon, 01 May 2023 19:16:49 GMT

Thanks Seth.

How to select "Include semirigid diaphragm node results" option for "Nodal displacements"? See below from "help". Thanks

RE: Effective Length Method

Seth Guthrie — Mon, 01 May 2023 17:02:53 GMT

Check the RamFrameAnalysis.pdf manual for detail on drift output, section 3.6.13 Drift. If the diaphragm is semi-rigid and you are using drift output, then yes the deflection of the diaphragm is included. If you are using nodal displacements and reporting for the nodes of the frames, then it's not.

RE: Effective Length Method

Qing Zhong — Mon, 01 May 2023 16:49:57 GMT

Does the drift include the diaphragm displacement? Does the nodal displacement include the diaphragm displacement?

RE: Effective Length Method

Qing Zhong — Mon, 01 May 2023 16:45:20 GMT

Thanks Seth. Thanks for your suggestions and help.

This is Jane and I am John's coworker. We are working on the same project.

What is the difference in drift output and nodal displacement output in RAM structural? Is there a Wiki discussion or community discussion on difference between drift and nodal displacement?

Thanks again!

RE: Effective Length Method

Seth Guthrie — Fri, 21 Apr 2023 15:24:47 GMT

There are some huge displacements of the semi-rigid diaphragm in this file, especially for the A/B roof 2 level. As such, the reporting of drift could yield some very large values depending where exactly you check for drift (in a semi-rigid diaphragm the program looks at the average displacements of the nodes of the element nearest to the control point). For this I would stick with nodal displacements because you have frames at the edges where you care most about deflections and because the diaphragms are all partial. You might also want to include the diaphragm out-of-plane stiffness under criteria - diaphragms. See: communities.bentley.com/.../ram-frame---semirigid-diaphragms-faq

RE: Effective Length Method

John Rodrigues — Fri, 21 Apr 2023 13:24:04 GMT

I uploaded my model (MSF.rss)

RE: Effective Length Method

Seth Guthrie — Thu, 20 Apr 2023 22:56:24 GMT

To upload RAM SS files use

Secure File Upload

When evaluating drift it's good to check the overall deflected shape first. Your semi-rigid diaphragm might be deflecting a lot causing unexpected ratios, for example. If the deflections are reasonable, but something is off in the torsional check it could be due to having control points that are off the diaphragm. You can always calculate these ratios manually using the drift or nodal displacement results.

RE: Effective Length Method

John Rodrigues — Thu, 20 Apr 2023 19:19:32 GMT

Additionally: This structure has a main portion with a semirigid roof diaphragm at one level and an attached portion with a semirigid roof diaphragm at a lower level. The intent is to have the lower portion of the structure rely on the high portion to resist lateral loads.

RE: Effective Length Method

John Rodrigues — Thu, 20 Apr 2023 15:53:03 GMT

I also tried uploading my model but it won't attach here.