Composite beam with OSB and gypsum board?? 2

[serdardundar]

Hi, happy new year for everyone...
I want to learn if anyone has utilized OSB (oriented strand board) as a load carrying member? I mean as a flange of a cold formed C shaped member, or as a web of two plywood members (screwed/glued at top and bottom of OSB).
An engineer in New Zealand, working in cold formed residential structures business , suggested that the strength of gypsum board (with high tensile capacity ??) which is used at the bottom of the joists as a ceiling finish and strength of OSB (with high compressive strength??) which is used at the top of the joists shall be added to the flexural capacity of the joists...
The joists are of C shaped cold formed (1-2 mm) steel members with low tensile strength (Fy = 33ksi). He suggests including the area of OSB and gypsum as they are flanges of the C shaped joist....
Do anyone has implemented such a procedure? Is there a code that allows such applications? Where can i find some code regulations, calculation procedures or examples for this case? And also where can i find dependable strength values for gypsum board and OSB?
Thanks for your help....

 

[DaveVikingPE]

US Gypsum has their construction handbook on the web at

http://www.usg.com/Expert_Advice/const_handbook.asp.

Here's a good site on oriented strand board:

http://www.osbguide.com/.

But...... They don't seem to have much, if anything, related to engineering properties of gypsum board (other than fire protection, that is). Frankly, I wouldn't consider a composite beam as you describe. As far as OSB is concerned, it's fine for floor sheathing, but as an element of a beam?

Technically, you could easily determine the properties of a composite beam from basic mechanics of materials, but I wouldn't go near using a combo of cold-formed steel, gypsum board and oriented strand board unless ASTM (and - not or - the equivalent in New Zealand and elsewhere), in conjunction with the various parties concerned, released some serious test data that, for example, indicated the tensile strength of gypsum board was even worth discussion. My own personal experience with gypsum board is that it has tensile properties incompatible with consideration as a structural material. I mean, if the upstairs neighbors' toilet is leaking, the water will bust through the sheetrock between the joists. Not only that, but it tends to deterioriate under various environmental conditions. Also, because of its workability, sheetrock lends itself to be easily removed, replaced, cut into myriad shapes, etc. Thus, I would consider it 100% unacceptable for consideration in load-bearing considerations.

Hence, go with the cold-formed joist only. If it's not enough, use a larger section or go with timber I-beams.

 

[Ron]

Oriented strand board works OK as the web member in a composite, engineered wood application. I would not use it or gypsum board as the tension flexural component of a composite member. Neither of these materials has good tensile/flexural capacity.

 

[serdardundar]

Thank you very much DaveViking. Your reply has been very helpful. More or less i thought the same way as you wrote. But i have seen a picture (just a picture nothing more) of a beam whose web is OSB (i don't know its height but 20-30cm approx.)and there are two timber rectangle solid blocks at top and bottom as flanges.I think the picture was taken from USA. I thought maybe the shear strength of OSB is dependable. Did you see something like this?
But i don't think i will use it as a load carrying member anyway...(neither as a flange nor as a web)

 

[Trussdoc]

Serdardunder, what you saw was probably a typical engineered lumber I-joist, very commonly used in the US and Canada. The web is OSB, which has a very reliable and tested shear strength, and is used for seismic resistance in walls. Flanges may be Laminated veneer lumber or sawn lumber for less critical applications.
The key to making these materials reliable is in the connection between flange and web. A combination of grooves and glue is used.
The advantage of this type of material over traditioonal sawn wood is dimensional stability, greater depth available for longer spans, and lighter weight. I believe that some of the manufacturers include the composite effect of a glued and nailed plywood/OSB floor in their design software and span tables.

 

[LPPE]

A lot of the I-joist catalogs include the subfloor as a part of their I joist in their load carrying capacities, and also include gyp board on the bottom of joists as a vibration reduction element.

 

[ishvaaag]

In any case is very risky the use of gypsum boards for any structural strength calculation. Forces at connections, nailed or glued, may well exceed the gypsum capacity; far worse in dynamic situations where nails/connectors may distroy the necessasry shear transfer out of built by the vibrations gaps at the connectors. Vibration AND deflection of the more fragile gypsum (even embedded in something) may crack the gypsum panels and then the gypsum board tensile capacity is taht of the external binding sheets if any. Furthermore cracks happen in gypsum at quite close distances once restrained, and once attached restrained will be, and this even if diminished will be ongoing and unseen under any external binding sheet not allowing to see that has happeneed.



However I would accept to account the different properteies of floors damping wise with and without the ceilings made of gypsum boards.

 

[DaveVikingPE]

I've seen the engineered wood I-joists mentioned by Trussdoc. I think they're great!

That being said, though, if span tables and such include the floor sheating in their calculations I would call-out a similar arrangement in my design. That is, if the span tables give spans for a "...particular joist...with 3/4" OSB sheathing..." I wouldn't at all assume I could get away with 1/2" floor sheathing. I might if I had all the data possible on OSB, but...

Ishvaag and pylko are right on the money about gypsum board. Sure it's fine for vibration damping - like noise from above - and fire protection, too, but considering the way plastic screw anchors behave in sheet rock I would never even think about using it as a load-bearing element. Well, it depends how heavy things like Track lighting are and such. I have used some "heavy duty" sheet rock anchors, rated for 50lbs each, though, with great results: my stereo speakers haven't fallen off my wall, for one. But a 12-lb speaker is a world away from a real structural floor load.

 

[felipe1]

hi i does anybody have information about the mechanical properties of osb i pretend to make a comparision between plywood and osb to be used as an I-beam i been trying to find this information and i have found some is just that i want to know wich values aply in this kind of aplication i know there is I-beam (joist made with lvl at the extreme as a flange)so please i will apreciate any information a bout osb and its mechanical properties as a beam