Suspended Walkable Ceiling Live Load 2

[BSVBD]

Designing a cold production and storage facility.

The Production Room inside the facility is to have a walkable insulated ceiling, suspended and supported by the roof Open Web Steel Joist (OWSJ) bottom chords.

One supplier said the live load could be 20 PSF. When i asked where he got that load information from, he said the code book. I don't see this anywhere in IBC.

One manufacturer said 30 PSF.

I intended to use 40 PSF for catwalks, per code, but, then the supplier stated that would be MUCH more expensive.

(For IBC 2009 Live Load Table 1607.1, please see attached...)

[URL unfurl="true"]https://res.cloudinary.com/engineering-com/image/upload/v1481044100/tips/LL2009_uvnije.pdf[/url]

In IBC 2009, what exactly does "Primary roof members, exposed to a work floor" mean? This walkable ceiling is intended for equipment maintenance, thus, could be construed as a "work floor". Could i justify this 20 PSF for a walkable ceiling?

Any suggestions on how i could justify 20 psf? Other suggestions?

Thank you!

 

[FoxSE14]

Just an idea: "Scuttles, skylights, and "accessible ceilings" = 200 LBS?. Haven't been down this road myself however.

 

[BSVBD]

Fox... Thank you.

I didn't notice the "accessible ceilings". I'll make sure i specify that point load on the framing plan. But, in addition, and primarily, I'm looking for a justifiable Live Load pressure.

 

[KootK]

Do you have a sense for how the space will be used?

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[structSU10]

We have used the 'Tuff T' system from metl-span. They have a load chart based on panel span and tee support span, with capacity going up to 49 psf. Based on their charts, for a 4" IMP, the panels could span 15' for 20 psf versus ~10' for 40 psf, so it is roughly 50% more support members.

 

[BSVBD]

Koot...

The insulated panel, walkable ceiling, will be used for an equipment maintenance access surface above a "clean room" for cold food production.

The ceiling will be accessible by a separate catwalk.

Does that help?

 

[BSVBD]

struct... Thank you... I'm currently checking into Metl-span.

At this point, I primarily need a code justifiable reference for using a preferable 20 psf pressure.

 

[EngineeringEric]

In my opinion, you are looking for a catwalk. the 40psf can be applied to only one area if you can delineate this space... to me the 20psf for trusses BC is because people will be walking all over the place, not in one single file line. If i do trusses with a catwalk in them, i state that area for a larger DL and LL.

 

[jayrod12]

I agree with EE, anytime I specifically have a catwalk in trusses where the loaded area is more controlled, I specify a larger live load.

 

[BSVBD]

Eric... Thank you for your input.

To avoid confusion, the walkable ceiling WILL cover the entire 120' x 120' Production Room. The client wants the ceiling to serve both as ceiling and maintenance access.

A separate catwalk will provide access to the walkable ceiling. For the catwalk, i WILL use 40 PSF.

I would be more than happy to specify a 40 PSF Live Load for the entire ceiling... BUT... when both the end client and the general contractor (my direct client) both have access to all Ceiling Panel Data and Spec sheets, they will demand an answer as to why i am specifying 40 PSF when the suppliers and manufacturers recommend the "typical" and historical 20 PSF. As structSU10 implied, the 40 PSF will result in considerably more support members, installation labor and cost.

Can anyone provide a code justifiable reference for specifying a 20 PSF Live load?

structSU10... when you used or specified the "Tuff-T" system, what Live Load did you specify? And what code did you reference?

 

[KootK]

I think that your path is to have done your due diligance and accepted that the design load is essentially up to you as a matter of judgement. In your shoes, I might go with:

1) 20 PSF and 200 lb and;

2) A look at how many workman might aggregate over each element based on that elements tributary with.

Frankly, I'd put more stock in #2 than anything else.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[azcats]

Could it be considered a 'roof' even though it's inside another building? Perhaps where the 20 psf was derived. It sounds like the usage would be similar to a typical roof.

ETA: Sorry - should have looked at the attachment before I posted. I'd probably say 300# and 20 psf is adequate for the usage provided the joists aren't exposed to below and the 2000# load in that table is indicated.

 

[Once20036]

I've done lots of these and have always designed the new ones for 20psf.
As you've found in the code, I believe that this is above and beyond what's required and will utilize the single 200lb point load if we're doing a retrofit of an existing building.

 

[BSVBD]

Thank you ALL for your input... VERY helpful.

Thank you!

 

[structSU10]

when we used it, the system was good for 38 PSF. It was based upon what the client had done in the past at a similar facility. We were basically told that is the arrangement / capacity they wanted. Due to that, we never dug too deep into any possible reduction to that loading.

 

[BSVBD]

struct... thank you again for further input.

The reason i tend to dig so deep and consider nearly every aspect is because, on a regular basis, i deal with very competent state plan reviewers and many competent members of the general contractor team.

 

[spats]

I've designed a few of these types of facilities, and the walk-on ceiling is typically designed for 20 psf live load. I don't think there is a code reference, just an industry standard. There is no need to design the roof joists supporting the ceiling for minimum roof live load plus walk-on ceiling live load, but you should combine roof snow with the ceiling load.

 

[SteelPE]

I just finished designing a similar system to this a few months ago. I went into the design thinking I should use 20psf. Once I started the design and read the code I made the switch to 40 Psf.

 

[spats]

40 PSF for everything or 40 PSF for the walk on ceiling?