Expansion Joints in large Warehouse Facility 4

[Betka]

I am designing a 500,000 sq.ft., 70'-0 high single storey steel framed 'big-box' warehouse facility. Plan dimensions will be 770'-0 x 650'-0. I intend to provide a roof expansion joint cutting the 770'-0 dimension in half but am wondering about the merit's of a second, perpendicular, expansion joint. This second joint would now render the steel deck diaphragm unstable without the use of either interior X-bracing (not desirable) or rigid moment frames (resulting in excessive column sizes due to the height of the structure).
Is that 'second' joint a good idea or even really warranted in a heated and well-insulated building?

 

[JAE]

650 ft. is a loooonnnng way. Check out the AISC manual and the chart in there suggests something like a max. of 350' to 500' (can't remember the max. but its about there somewhere).

I would suggest that some braced bays along the expansion joints would be highly desirable....70' high is very high....a moment frame would be ridiculously expensive and large....

 

[Betka]

Thank's JAE.
I think I knew that I was going to agree with that point of view... just don't know how to tell the client that I need to introduce X-bracing into the middle of his facility.

 

[WillisV]

The chart JAE is referring to originated in the Federal Facilities Council Tech Report No. 65 which can be found free online at:

http://darwin.nap.edu/openbook.php?record_id=9801&page=R1

There are many other factors besides length that go into if an expansion joint is required or not. Also it is possible for a warehouse type structure that perhaps can take a good bit of movement to actually take the forces generated by the thermal expansion within the braced frames. Be careful with this though as they can get quite high and for this length of building could control the brace design over wind etc.

 

[lkjh345]

Betka:

Agree with the others.

FWIW: A few years ago I was helping another engineer in our office with a large warehouse. After some phasing constraints dictated some of the expansion joints in the building, we were left with a final phase of approximately 500' x 600'. We finally talked ourselves into the 500' length without an expansion joint, but couldn't live without breaking up the 600' length.

The problem is not so much after the building is in use and is heated, as then thermal expansion is limited, but it is during constuction. In our part of the country, it can be 100 degrees in the summer and below zero in the winter. These buildings are relatively simple to build, but due to their shear size can take many months to complete. Easily a couple of seasons can pass during construction, so they experience wide tempature swings.

Will this be a facility where storage racks are going to be installed?

 

[Betka]

Thanks to everyone for their advice.
The Tech report was an especially good reference.
I am going ahead on the basis of two (perpendicular) expansion joints, effectively dividing the building into quarters.
I will X-brace the longest direction and try to keep the perpendicular joint free of bracing by using the diaphragm action of the (cantilevered) steel deck.
Guess I should try to restrict the movement to about h/500.

 

[Loui1]

I can see how bracing three sides of each diaphragm (each quarter) might work, but not just bracing two sides in the long direction. How did you get that to work out?

 

[Betka]

What I meant to say was that each quarter will be braced each way around the perimeter of the building. Now by bracing both sides of the interior two long halves (ie. one on each side of the transverse joint) I will effectively have four quarters, each with 3 sides braced. All four quarters will now only have one (interior) open side which (hopefully) will be held rigid by the steel deck diaphragm.
Sound O.K.?

 

[Ron]

Betka...don't forget that the roof membrane system needs a joint about every 200 feet (doesn't have to be a structural joint, but the two must be compatible), but don't run joints in two different directions unless the slope and drainage are considered (Don't want ponding in odd places!)

 

[Betka]

The perimeter of the roof and the (crossed) expansion joints through the center of the building will be the high points.
There will be a series of roof drains along the valley lines created by lowering the beams or girder trusses (about 6"). The roof membrane will be an EPDM ballasted roof system. I believe it should have enough flexibility to span the 350'-0 +/- uninterrupted.