huangyhg

bracing in a freezer building
i鈥檓 working on a freezer facility. the primary framing is steel. it is approximately 275鈥?x 325鈥? i鈥檓 looking at 鈥榅鈥?bracing for wind loads. seismic is small in comparison. it is being built in texas. the operating temperature is zero f to minus 15 f. the steel has a potential swing of 75-100 degrees. right now i鈥檓 looking at 3-4 bays of 鈥榅鈥?bracing. the 鈥榅鈥?bracing would be in consecutive bays. the problem i鈥檓 finding is the outer columns have extreme uplift loads from the temperature swing. the steel at the roof level contracts horizontally and doesn鈥檛 at the foundation. the 鈥榅鈥?wants to resist this movement. this in turn causes large uplift forces on the outer columns of the bracing. i鈥檝e looked at several different bracing layouts and still end up with the large uplift forces.

i鈥檓 hoping there are others who can give me insight into freezer building bracing systems that can accommodate the large temperature swings. i鈥檓 also looking for resource on the design of freezer facilities from a structural standpoint. i did a search of aisc site and didn鈥檛 find anything. are there any good articles or books on freezer building design, particularly the structure?

thanks for your help.
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we usually provide a single x brace in the center portion of the freezer to avoid a build-up of axial forces in the collectors at the roof edge. i'm not sure i understand your column uplift scenario.
try to avoid the multiple x braces in a single section of the freezer.
one set of rod x-braces per row of bays is my rule of thumb for preliminary lateral force design. why is there a temperature shift of one hundred degrees? the insulated wall location should have no penetrations of steel beams. thus double,(or triple columns), at change of temperature locations with simple spans are the standard.
i put in multiple sets of 'x' bracing because the uplift force from overturning for one set was very high. i need to add a drilled pier or something like that for the wind overturning uplift force. the 0.6d + 1.0w combination produces a lot of uplift. the roof elev. is +31.00 ft above floor.
the steel is inside the insulated metal wall panels. this is why the steel goes through the temperature range.
looks like a single 'x' brace with piers for uplift will be best. any other sugestions for the wind uplift resistance?
thanks.
how about if you us compression struts in two bays as
l/l\l
jae's pretty much on the mark with a single line in the centre in both directions. also have used bracing one clear bay in if uplift is a problem. because of the height, uplift often becomes an issue and generally easily accommodated by friction piles (common foundation in this area).
dik
rlewistx,
is this one big box? or are you breaking it up into multiple freezers? if it's broken up then you can engineer single boxes with windward wind only since the leeward wind would apply only on the "other" box downwind.
this is one big box. there is a small room inside for ice cream storage where the temperature will drop to -15 f. the remaing room space is zero f.
i ran the compression strut model over the weekend too. it came out with slightly less uplift forces. i've never used one before. any cautions as to why i shouldn't?
thanks for your help.
rlewistx,
if you do the two compression struts starting at the top of the same column and then sloping away in opposite directions, then you get only one point of thermal restraint, but 2 bracing bays!
the reason why this type of bracing is not as common is because it is more expensive.
how does the steel temperature generate uplift in the columns? the temperature of the room and the steel is constant at whatever temperture is set.
the bracing causes uplift because the top of the column is free to move horizontally but the bottom is fixed to the foundation. the roof beam shrinks. the 'x' bracing wants to restrain the shrinkage. it ends up putting an uplift force in the end columns. the more bays of bracing you have, the greater the force on the outer columns. i wish i could post a graphic to illustrate it.

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