Timber sheeting as diaphragm?

[LunaPark]

At floor level, can timber sheeting be treated as diaphragm to transfer wind load? I have seen plans that edge beam (parallel to floor joist) not considering wind load applied to its weak axis? (6 metres long beam with 300x45 LVL ONLY) Is it because that the timber sheeting can be used a diaphragm so no need to consider wind for edge beam? (no internal blocking provided between edge beam and floor joist) I am not familiar with timber, can anyone help? I am in Australia if that matters. Thanks.

 

[BAretired]

Yes, timber sheeting is commonly used as a diaphragm to resist wind load on a floor or roof. If the sheeting is adequately connected to the top of a perimeter beam spanning parallel to the joists, the top of beam may be considered laterally supported. Without blocking between edge beam and floor joist or some other means to prevent beam rotation, the bottom of the beam is not laterally braced by the sheeting.

BA

 

[LunaPark]

Thanks BA. Is it a normal practice to not provide internal blockings between edge beam and the adjacent floor joist? Like you said, without restraints at bottom, the edge beam is like the 'slab' with 3 edges being restrained, in which case can wind analysis on edge beam be ignored? Do you purely treated the edge beam as part of the framing to transfer wind to the sheeting without worrying about the twist of the edge beam under wind load? If not, what is the simple way to comp the edge beam under wind load?

 

[BAretired]

Do you purely treated the edge beam as part of the framing to transfer wind to the sheeting without worrying about the twist of the edge beam under wind load?

That would not be acceptable unless the wall below is made continuous with the beam so that the wind reaction is delivered to the top of beam, then to the deck.

If the wind force is applied to the bottom of the beam, internal blocking between beam and joist would appear to be the simplest way of preventing beam rotation.

BA

 

[LunaPark]

Thanks BA. No, walls are not continuous. So if not internal blockings are provided, do you take the entire length of the beam as simply supported to comp the wind, ignoring the sheeting restraints on top for the sake of simplicity? (This beam is actually designed by the truss manufacturer not by me but I am just concerned).

 

[BAretired]

The truss manufacturer is not the Engineer of Record (EOR), so it's not clear why he is designing beams. If you are the EOR, specify internal blocking at suitable spacing. If you are not the EOR, what is your involvement in the project?

BA

 

[LunaPark]

The truss manufacturer is involved in designing the truss together with the timber members within floor cavity. Anything else like steel beams, columns, bracing is done by me. I am not sure whether it is common to not provide internal blockings but apparently the client has been using this manufacturer for many projects and I have seen the previous projects that have been designed and built this way.

 

[gte447f]

In my experience, it is fairly common to encounter wood floor system that do not have blocking between the stringer/rim joist and the first common joist that is parallel to it. However, I do not consider it best practice to omit this blocking. The blocking is needed to properly transfer wind loads on the walls to the floor diaphragm, unless the stringer/rim joist has really been designed as an edge beam for out of plane loads.

 

[MotorCity]

You will take a big hit on the capacity of an unblocked vs blocked diaphragm.