A truss designer on the project I a 2

[strucguy]

A truss designer on the project I am overseeing is trying to convince me to not make them consider the weight of partitions in their truss design based on the following excerpt from TPI publication. Has anyone run into this issue before?

ANSI/TPI 2002, Section 2.2.5, “The weight of non-bearing partitions shall be permitted to be ignored for truss design purposes given the following conditions; if the following conditions do not exist, the Building Designer shall specify in the structural design documents the non-bearing partition loads that need to be applied to the trusses:

(a) Trusses are not spaced over 24 inches on center;
(b) Top chord panel length of supporting trusses does not exceed 30 inches;
(c) Design live load of supporting trusses results from a residential occupancy and is not less than 40 psf;
(d) Partition weight does not exceed 60 pounds per lineal foot; and
(e) When partitions parallel to supporting trusses are not located on or immediately adjacent to a truss, the sub-floor shall be of adequate strength and stiffness to support the partition load, or other provision shall be made to distribute the partition weight to the supporting trusses.

The truss layout for the project satisfies all the conditions above, and the designer wants to ignore the partitions loads in their truss designs. But, I am not sure if this is in compliance with the building code. Your feedback is greatly appreciated.
Thanks.

 

[Michel60]

Good afternoon strucguy,

TPI 1-2007 is a referenced standard in IBC/CBC. I'm not sure if its the same or similar to what reference you have been provided, but in either case I would key on the phrase "...shall be permitted...". If your documents specify a partition load be considered then I'd say there is no question, it is to be included, full stop. But if you have nothing noted then you're probably in a bit of a tight spot. You can say do it but how hard do you want to fight for it? The implicit thing in the conditions is that given conformance with the limitations the resulting design should be satisfactory.

regards,
Michel

 

[strucguy]

Thanks for the prompt response, Michel. Our contract documents clearly indicate to either consider uniform partition allowance of 15 psf or use the actual weight of partition walls in the design of trusses. So, I am definitely covered that way. But, I don't want to be unreasonable by discrediting an approach that has worked before and is in compliance with the building code. I don't have the TPI 1-2007 with me. Can anybody tell if the language is any different to what's indicated in 2002 edition. Thanks again.

 

[Michel60]

I don't happen to have it either. I just took a look on-line and unfortunately it's a $70 bill to see the answer, but I suspect it's pretty much the same.

Since you have clear instructions to include the load I believe stepping back should be accompanied with some advantage to the Client. What you've provided them is future flexibility in their floor plan by not fixing limits on the interior partitions. If they want to give that up then there should be something offered in trade like cash, schedule...or maybe just future goodwill?

regards,
Michel

 

[nutte]

What's the applicable building code? Is it industry standard to provide partition load in a residential structure? The International Building Code talks about a partition load "in office buildings and in other buildings where the partition locations are subject to change." To me, this doesn't mean it applies to a residential building. If your code is the International Residential Code: does the IRC even say anything about providing for a partition allowance? You would include the weight of fixed partitions in your dead load, but this is different than a live load to cover future partitions.

 

[strucguy]

Michel, thanks for trying.

nutte, The building falls under IBC 2009.

 

[TXStructural]

TPI cannot change loading from the required values. As the design engineer, only you can change the design requirements, with the approval of the AHJ. IBC 2012 and ASCE 7 require the application of actual partition loads as dead load or a uniform live load increase of 15 psf for floors with a uniform live load of 80 psf or less. (The IBC structural committee has accepted a proposed change to the provision to make the provision "less than 80 psf".)

The plate-connected truss industry has historically placed designers in a bad position. TPI has been trying to delineate responsibilities so that the contractors, designers, and manufacturers each know what is expected. One of the serious problems in the industry was the lack of this delineation, which resulted in improper design loads and construction defects. Because of this, you should be clear that the design should, at your discretion and your selection, either use actual partition locations and loads, or the 15 psf increased uniform load. Be sure the sealed drawings from the manufacturer (usually the plate manufacturer or a contract engineer) specify the correct loading and brace points. Also, have a way to verify the quality of manufacture to assure the use of the proper plates, grade of wood, and similar items (just as you would for bolted connection.) Once erected, verify the integrity of the trusses and bracing. Properly designed, manufactured, and installed plate-connected trusses are an economical construction method, but they are vulnerable to bad design, manufacturing defects, and construction damage.

 

[woodman88]

I will assume that this is for a custom residential home. As most residential tracts do not assume partitions, that are going to be subject to location change, so the builder can pocket the lower cost of the floor trusses.

The big question is what is the job phase?
If it is in first bidding that they are trying to give the client a lower bid on the job. Saving the client a little money. But all the bidders should be given the same chance.
If the job is starting then it comes down to the fact that the Truss Company, most likely, missed bid the job. Much less likely, the Truss Company and/or contractor (most likely the framer) is trying to increase their profits a little.
The cost savings is so small that unless you are building a hundred homes (which is why tracts do not use partition loading) it is not worth it for individual owners. Also, the savings being so small, helping out the Truss Company will only encourage them to do it again. While increasing your liability as you are down sizing the quality of the house.

Personally, I have never seen the partition load being used in a custom residential building. But that is the owner/architect/engineer's decision.

Garth Dreger PE - AZ Phoenix area
As EOR's we should take the responsibility to design our structures to support the components we allow in our design per that industry standards.

 

[strucguy]

TXStructural and woodman88, thank you for your input.

The project is a 3-story multifamily residential building.

 

[TXStructural]

If this is an apartment or hotel style building, you know exactly where the walls will be, and they are likely uniform on each level, so the partitions may or will carry progressively heavier loads to the ground. Even if it not designed to do that, deflection of floors will load partitions set on continuous trusses. The trusses probably need to have vertical members to span between partitions above and below, unless the bottom floor truss is strong enough to carry the upper floors and associate loads. Watch the load path once floors deflect when the partitions are full height (from truss above to truss below.)

 

[strucguy]

TXStructural -

For partition walls on the project we asked for Simpson STC clips to avoid any loads being transmitted to these walls due to the deflection of the floor above.

 

[kipfoot]

I don't want to hijack the thread, but I'm interested to know how it turned out with the STC clips. I specified these clips with the provision to keep the partitions 3/4" below the trusses and got severe blowback from both the builder and the architect. They're framing the partitions tight to the trusses despite my recommendation. I got the age old, "we've always done it this way and never had a problem."

I'm on record with my reasoning and recommendation and I acknowledge that it creates a fussy detail for the drywall and fire rating. But, whew!

 

[strucguy]

kipfoot -

The contractor didn't have any issues providing the STC clips specified. I guess they have become a norm in the area I am at.

 

[dik]

from my General Notes:



PARTITION LOADING ALLOWANCE HAS BEEN EXCLUDED. PARTITIONS SHOWN ARE FIXED LOCATIONS AND ALLOWANCE IS INCLUDED IN THE DESIGN. ALTERNATE PARTITION LOCATIONS TO BE REVIEWED BY [CONSULTANT | ENGINEER]

The NBC of Canada has loading provision for partitions that are not fixed. And by stipulating that they are fixed, the general partition loading is not required. Sometimes for office buildings, I'll roll it into the live load to give a slight added flexibility.

Dik

 

[oldrunner]

For trusses deflecting, I believe TPI has a paper or advice for the nailing patterns for the ceiling gyp board at the non-bearing wall intersections so that when the trusses deflect (when you are using the Simpson STC clips) doesn't rip the tape.

 

[nhstruct]

I have just delt with this on two projects. If it is stated on the drawings they must provide it. We carry it as a live load, as MA building code requires it. We usually get a call from the truss designer with the comme ts you mentioned, I just let them know that iBC requires it and they must provide it. As far as the STC clips I never had a contractor/Architect argue that the partition walls are to be tight to the truss. I had a recent project where the trusses were very bouncy, mainly due to the depth to span ratio. The truss manufacture said to frame the partition walls frame to the trusses, much to the disagreement of me and the architect.