Unistrut Properties Calculation 1

[DeemsSE]

I have a project in Los Angeles in which I have specified a considerable amount of unistrut. I specified the unistrut based on the published allowable values in the Unistrut catalog. LA plancheck is requiring calculations verifying the allowable properties shown in the catalog since Unistrut does not have a LARR report. Has anyone come across this issue before? It seems odd that we have to provide cumbersome AISI hand calculations to justify tables that have been used for decades without a problem. Even OSHPD and DSA are OK with the published Unistrut tables. Any thoughts would be appreciated. Thanks!

 

[Ron]

Warm up your slide rule and sharpen your pencil...if they require it, you'll likely have to do it. Any help from Unistrut?

 

[DeemsSE]

The unistrut rep said the Unistrut would not provide back up calcs to support their tables. Next time I may just use struct steel!

 

[Ron]

Unconscionable of Unistrut not to offer to back up their tables. I would use something else as well.

 

[RacingAZ]

Are you talking about the section properties? You can do that easily if you have the Enercalc program. If it is the allowable load values that they are questioning, you can calc those based off Uni-strut's published section properties.

Another tack to use it to find the plan checker's supervisor. The supervisor being more senior, he/she may have a lot more history dealing with Uni-strut and might be agreeable to your argument.

http://www.dfoxonline.com

.....executing your vision.

 

[jberg]

Depending if the Unistrut has holes punched in it, I think you would need to determine the net (effective?) section properties as well as the gross section, which I believe is what they publish. From what I remember the few times I have done cold-formed steel design, determining the effective properties can be very daunting.

I agree with Ron, if Unistrut publishes the load tables, they should be able to back up with calcs if requested. You mentioned you spoke with a Unistrut rep, was that person in the Engineering department? If not, I would recommend calling them back and ask for their Engineering department and see what that yields. Might not help, but it is worth a shot.

Joel Berg

 

[DRC1]

Unistrut is big among electrical transmission people. I would contact the engineering department of whoever handles the power for LA. They have probably come across this and invented a wheel to solve this. They will probably be willing to share, but it may cost you a beer or two.

 

[racookpe1978]

Problem will be that Unistrut can't really "calculate" their total properties because the tip (ends) of the Unistrut fold over in a rolled-U bend: The U makes the end of each wall much stiffer against twisting and bending in-plane than a if you assume a straight-walled "channel" of the same metal type and thickness.

Unistrut "holes" also cause theorectical issues: Who is the "LA plancheck" and how do you protest his/her/its excess requirement?

 

[msquared48]

Do they have an old ICBO report that could serve as backup? I agree with Ron here on the lack of backup by Unistrut.

I can't believe that in this economy that they are that busy that they can afford to lose customer base to competitors.

Bad marketing and real bad business plan. Bad, Bad, Bad.



Mike McCann
MMC Engineering

 

[racookpe1978]

I can't understand the fundamental reason why a "calculation" is being required in the first place: if you design per references a long-recognized catalog, using values assigned from that catalog that have been well-established - for what? 45-60 years of service in hundreds of thousands of applications without failure - then why "approximate and calculate" the weight, moment of inertia, stiffness, etc?

Better, more accurate values are already available. It would be equalto requiing I calculate the properties of a I beam or channel because the two webs have a slight angle to them.

 

[Ron]

racookpe1978...there's not much to understand. It is a government agency born and bred on procedure. The reviewer is often not an engineer or an architect and is usually not allowed to interject judgment into a procedural process. I've not dealt with LA, but Miami-Dade is pretty much the same, and many of the smaller building departments are getting that way as they become more "sophisticated" in their plan review process.

I could find no code evaluation report for Unistrut.

 

[Ron]

DeemsSE...on the Unistrut site, they have a section that shows how certain calculations are performed for various sections. This might be sufficient documentation for your approval. Here's the link...

http://www.unistrut.com/tech_data/index.php?P=Tech

 

[rowingengineer]

Ron,
I do believe you have above and beyond the call, Hope you get invited to the Unistrut Christmas party for doing a better job than the rep.


When in doubt, just take the next small step.

 

[Ron]

RE...Thanks. I'm surprised that a company of such long standing has no product approval/evaluation reports. Seems like everyone has them...but not Unistrut. If someone wanted to push the issue, they could not provide Unistrut in Florida...no Florida Product Approval.

Corporate arrogance I suppose.

 

[Gumpmaster]

Can you maybe get better responsiveness from Tolstrut or B-line stut? Tell them that Unistrut is unwilling to provide calculations, but you're willing to specify their product if they help you out.