High uplift/horizontal loads in a Freezer Building
High uplift/horizontal loads in a Freezer Building
(OP)
Hi All,
I am designing a large cold warehouse (100x100m) consisting of a standard steel beam to column frame. The building is operating at -30 deg. The frame is pinned and braced X as a big box. I did a 3D stick model, applied a drop temperature of -50deg to each steel member (assuming ambient temp of 20deg) and I was shocked to find out that I have 2000kN tension force in the gable X bracing. This high tension is transfered to my corner columns. I would have to design a baseplate for a such impossible to resist force (uplift and horizontal shear). I wonder if anybody can help me on this. Maybe I am doing something wrong, as those warehouses/cold stores as built all over the world.
I also noted that I need to isolate the baseplates with a thermal breaker. That means that I need to have two baspelates offset and connected by holding down bolts. How even small horizontal forces can be resisted on 4 small bolts, they will fail in bending. Not sure if I am missing something here too?
I appreciate your help.
Kind Regards
Karol






RE: High uplift/horizontal loads in a Freezer Building
Don’t all the steel members expand and contract at the same rate? So, relative proportions don’t really change much. It sounds like you didn’t adjust the temp. on a few member, or some such. You may have to adjust the turnbuckles on the x-bracing as the interior comes down to its -30̊ temp. to tighten the bldg. up laterally. And, you likely will need to do this, because if you are using insulated rigid panels as the exterior skin, they are very good shear panels and will try to take the lateral loads if the x-bracing doesn’t. This racking just blows their gasketed and interlocked joints out. I’ve seen 4' wide x 20' high icicles hanging off the sides of bldgs. at these broken joints. The frame lateral delta must be limited. And, the connections btwn. the frame and the panels must be designed to take this kind of differential movement.
The steel frame x-bracing takes most of the lateral loading, except for some shear reaction on each individual column due to wind or EQ acting perpendicular to the wall plane. There are hard foam or ceramic bearing blocks which go btwn. the column base plate and the concrete column pedestal, and you put a small shear stub on the underside of the base plate and down into the pedestal, and then the regular A.B’s. You also have to heat the underfloor sub-grade to prevent it from freezing over time and heaving. Talk with a couple suppliers of the wall panels which you might use, they will have a wealth of detail info. for you.
RE: High uplift/horizontal loads in a Freezer Building
RE: High uplift/horizontal loads in a Freezer Building
Mike McCann
MMC Engineering
RE: High uplift/horizontal loads in a Freezer Building
Think of an exterior wall of framing where you have 9 bays (10 columns connected by roof beams).
The center bay has an X-brace with 4 open bays on either side.
When frozen, the outer four bays on either side "freely" shrink inward and are not resisted by any X-bracing.
Thus you don't have temperature induced high forces at the base of your columns.
The worst thing you can do is put X-braces at the corner where thermal shrinkage causes them to fight each other.
RE: High uplift/horizontal loads in a Freezer Building
Mike McCann
MMC Engineering
RE: High uplift/horizontal loads in a Freezer Building
dhengr: In my model I applied uniform drop temperature of -50deg to each member including bracing. The building contracts due to shortenning of the steel members. Could you please advise what do you mean by adjusting the temperature on a few members?
RE: High uplift/horizontal loads in a Freezer Building
Mike McCann
MMC Engineering
RE: High uplift/horizontal loads in a Freezer Building
RE: High uplift/horizontal loads in a Freezer Building
A 50 degree C change in temperature equates to a change in length of about 58mm in the 100m length of your building, say 25mm from each end to the middle bracing bay. Allowing for this movement is much preferable to trying to overcome it.
In my only experience with a large freezer building, the building enclosure was separate from the freezer, building within a building.
RE: High uplift/horizontal loads in a Freezer Building
I did a similar thing to a long pipe rack that was "Hot-boxed" instead of heat tracing the individual lines.
Michael.
Timing has a lot to do with the outcome of a rain dance.
RE: High uplift/horizontal loads in a Freezer Building
Michael - there are multiply doors so wont have the continues ring beam.
Maybe applying -50deg to each member is incorrect approach? I would imagine there is an answer as there are cold stores built everyday.
RE: High uplift/horizontal loads in a Freezer Building
As I said, there is something wrong with your model. Just increasing a brace size does not increase the force due to volume change. The type forces you are experiencing suggests that you are modelling the eaves struts with pins rather than rollers, i.e. not letting the columns lean. Do you agree with my second paragraph above?
RE: High uplift/horizontal loads in a Freezer Building
I didn't know enough about the rooms in my previous post, I assumed there would be a framed floor with part of the cooling system beneath it.
Michael.
Timing has a lot to do with the outcome of a rain dance.
RE: High uplift/horizontal loads in a Freezer Building
Michael - without thermal effects the loads are max 200-300kN (much smaller comparing to 2000kN). If I put columns on roller they will just sway due to wind action and I need to comply with H/360 for this building. So on one hand I would like very flexible frame, but from another side it needs to be quite rigid to comply with this delta limit.
RE: High uplift/horizontal loads in a Freezer Building
http://www.amscotnj.com/pdf/Amscot_ABG_Guided_Cata...
Michael.
Timing has a lot to do with the outcome of a rain dance.
RE: High uplift/horizontal loads in a Freezer Building