FTAO: Thompson Method vs. Diekmann Method

[skeletron]

During some recent waiting room downtime I decided to decipher the SEAOC Volume 2 guidebook (IBC 2015) and look at how they set up the FTAO calculation. I am familiar with the APA's Diekmann method calculator tool and wanted to have a side by side comparison.

A couple of short questions:
1. The SEAOC example doesn't care about the A.R. above the opening. However, when looking at Malone's Ex.10.4, he checks that aspect ratio and disregards the portion above the opening.
Does the Thompson method disregard the A.R. check because it attributes the wall up to inflection point to the pier?

2. Why is the Thompson method hold down force 200 lbs, but under the same conditions the Diekmann wants to attribute 1000lbs?

3. If there are unequal depth openings, is the Cantilever beam analogy more applicable? Thompson and Diekmann methods seem to need the consistent opening depth assumption.

For reference, the example wall from SEAOC is:
L1, L2, L3, L4 = wall piers = [8, 12.75, 11.5, 11.5] ft
O1, O2, O3 = openings = [9, 4, 4] ft with consistent depth of 4ft, 2.54ft above grade
F = 7612 lbs applied to the wall line
H = 8.21 ft

 

[skeletron]

Kind of figured out #1 by looking at some of the warnings that do pop up on the APA calculator. It seems that they flag a warning when the above/below sections are > 6.5:1 because of the assumption of fixity of the corner. Makes sense because as that opening gets longer there would be more flexibility in that section.

 

[phamENG]

Have you read this document? Gives a good breakdown of various methods and all arrangements and sites a comparison to test data.

 

[skeletron]

Yes I have downloaded that Skaggs paper and watched the APA webinar that goes through this. The paper seems to focus on the strap forces and doesn't mention the hold down force. I think the SEAOC Volume 2 example is a little wonky tbh. There are some text mistakes, but they also resolve the hold down force in the first pier. Whereas Diekmann's method is the whole wall. I understand that fundamentally Diekmann treats the wall as a monolith, where the Thompson method tries to resolve it separately into the rigid bodies between inflection points.

My questions are more out of curiosity with some of the text examples (SEAOC Volume 2, Malone's Irregular Analysis book, APA's calculator) and why the "wires are crossed" when it comes to some of the calcs.

 

[milkshakelake]

I've relied more on Malone's methods than Deikmann's, but I don't think either one accounts for flexibility. They just use aspect ratio instead of a finite element approach, and I think that's fine because like, what else are you gonna do? For large openings with tall walls, I'd use Malone's chapter on Portal Frames.

I think you can just email Malone this question. I've had email conversations with him and he's pretty responsive. He can probably explain this way better than I can. I don't remember this exactly, but I think he also went over Deikman's method (or maybe I'm confusing that with Breyer), but either way, you can go straight to the source.

I'll just say my own opinion. I don't think either of the approaches are correct and they both feel wonky. However, it's really the cutting edge right now, so I say pick one approach and stick to it. I just overspec every strap and holdown in my design, and I've gotten no complaints so far.