Open front steel deck diaphragm
Open front steel deck diaphragm
(OP)
Let's say I have a commercial box building, 55' wide x 150' long x 20' high. Steel frame, bar joists with metal deck clear spanning the 55' with wide flange girders and 6" tube columns and light gauge infill. I have chevron bracing on both 55' walls and on one of the 150' walls. The front end is all storefront. The chevron bracing and diaphragm are stiff enough so that any sort of moment frames I put on along the storefront side take little to no load and my chevron frames can take the torsional diaphragm forces no problem. My question is should I still include some moment frames along the storefront end for general stability purposes, or just go straight pinned with all the connections? I'm not completely sure what the general practice is here. Also I'm not in a zone with no seismic and low wind.






RE: Open front steel deck diaphragm
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.
RE: Open front steel deck diaphragm
Dik
RE: Open front steel deck diaphragm
RE: Open front steel deck diaphragm
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.
RE: Open front steel deck diaphragm
Dave
Thaidavid
RE: Open front steel deck diaphragm
RE: Open front steel deck diaphragm
With a 15 psf wind load, the shear (wind blowing on the side) is only about 55 plf is I am doing my math correctly. I would go three-sided and make sure your I's and T's are dotted like KootK suggested.
RE: Open front steel deck diaphragm
Dik
RE: Open front steel deck diaphragm
DaveAtkins
RE: Open front steel deck diaphragm
I have about 4-5 feet in between storefront so I could theoretically fit some frames in if the architect will go for it, but I think thaiDavids point is valid about leaving room for possible future renovations. My girders along the front end are supporting brick above the storefronts so they are fairly deep due to deflection restrictions, W27x84 at 25' bays. So I will probably go with rigid frames and use a W8 or W10 column as Dik suggested. I'm thinking of going with end plate bolted moment connections, it seems like a simple connection and I feel like the fabrication/erection costs wouldn't be much higher than a simple shear connection.
Anyway, to me it feels like there's not really any way to justify putting lateral resistance along the line other than "it feels right", and it's easy to agree with even though the numbers say otherwise. The stresses in the diaphragm are going to be much high when it's in a simple span condition resisting wind forces perpendicular to the 150' dimension, and no one's going to bat an eye at that. I get that the open front diaphragm is relying on torsional force and is going to twist on my frame, but I have 1 story Chevron frames with 0.8:1 aspect ratios so they're not going anywhere. Ultimately I know the rigid frames im putting in won't have the stiffness to actually attract any significant load but my boss wasn't going for the 3 sided diaphragm anyway. I have a tendency to where if more than one person is telling me not to do something, even if I disagree, it's hard for me to ignore it.
RE: Open front steel deck diaphragm
I'm assuming you are referring to adding another brace on the backside where I already have one? I was considering that just for redundancy since it's a fairly long stretch. Is that your reasoning as well?
RE: Open front steel deck diaphragm
- redundancy
- if that line is to do all the work, I like it wicked stiff.
- if that line is to do all the work, I like to avoid long collector slip accumulation.
- back when machines were dumb and judgment reigned supreme, common wisdom was a brace every fourth bay or so. Guessing 25-30 ft bays.
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.