Metal Building Sheathing Values

[CBSE]

I've done quite s few metal building foundation designs but haven't really put much thought into the wall and roof diaphragms.

How do they justify the sheathing with purlins and girts at 4ft on center. I have never been able to find values for this. Maybe I'm not looking in the right spot.

 

[hokie66]

Sheathing should not be used for bracing, IMHO. Sheathing is for watertightness.

 

[CBSE]

I don't disagree, but the load has to get to the x-bracing and columns somehow, and that has to be through a diaphragm. It's resting to me. I just did my special inspections on one and got to thinking about it.

 

[KootK]

Is there no horizontal roof plane cross bracing at the far ends of the roof?

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.

 

[SteelPE]

From what I understand, from speaking to some who have worked in the industry, your typical screw down roof does have some diaphragm strength... at least enough to brace the top flange of purlins and rigid frames under positive bending..... of coarse, this only works form screw down roofing not standing seam roofing.

You have to remember a few things about metal buildings, the rigid frames are used as part of the LFRS. End wall bracing is typically used to resist lateral loads that accumulate in the last 1/2 bay only. In the other direction, you will typically see side wall bracing. From what I can recall, the manufacturers use horizontal roof bracing the distribute the lateral loads to the side wall.

 

[msquared48]

Generally, the mainframes themselves take the lateral load from the normal walls, with little to no need for roof diaphragm action in the interior. It appears to me that any internal X bracing is provided for a more uniform deflection of the mainframes. If there is a more substantial gage of sheeting provided than 29 gage, this is probably not the case. However, at the end and side walls, there is a need to develop shear forces into the side and end walls - more so along the long side walls than the end walls. I never rely on the metal sheathing for any shear values unless it is at least 22 gage, but that is my professional judgment, which I am allowed.

Mike McCann, PE, SE (WA)

 

[CBSE]

If you are relying on the metal sheathing, and I have done this for pole barns, where do you get shear values for purlins/girts spaced at 48" o.c.? I have only found values for 24" o.c. spacing.