Building Expansion Joint Sizing

[Galambos]

I was curious how most are sizing building expansion joint widths in seismic design category A, B and C buildings.

Are you sizing it for thermal movement, amplified seismic movement, a combination of the two, or another method?

 

[JAE]

I usually look at wind or seismic (I'm in A, B or C generally - sometimes D) and use SRSS of the two adjacent structures for whatever gap I get.

 

[structSU10]

I do the same as JAE. I have not found thermal to control expansion joint sizes on the projects I have done, but I have only had to deal with a handful of expansion joints myself. I also like to add in a bit for some construction tolerance.

 

[msquared48]

I usually go with 1.5X to 2X the combined lateral movement due to seismic and let the Architects cry over the joint created.

Mike McCann
MMC Engineering

 

[TDIengineer]

ASCE 7-05 does not allow SRSS when sizing the building separation from seismic loads. Per 12.12.3 the separation is equal to the amplified drift of both structures added together.

 

[wannabeSE]

ASCE 7-10 requires the SRSS be used as a minimum separation. I think the SRSS was in the 97 UBC. The 2009 IBC also uses the SRSS (eq 16-45). FEMA 750 C12.12.3 recommends the SRSS and "For very rigid shear wall structures with rigid diaphragms whose lateral deflections cannot be reasonably estimated, it is suggested that older code requirements for structural separations of at least 1 inch (25 mm) plus 1/2 inch (13 mm) for each 10 feet (3 m) of height above 20 feet (6 m) be followed." Note: the drift used for building separations is typically the maximum inelastic (amplified) drift with torsion.

 

[TDIengineer]

My jurisdiction has not adopted ASCE 7-10 yet. The California Building code also allowed a smaller expansion joint sizing by using SRSS.

If you have 2 moment frame buildings abutting, and you're under ASCE 7-05 the additive rather than SRSS combo for amplified drift yields ridiculous widths in my opinion.

I wish I could have used SRSS...

 

[Lion06]

I've always used twice the maximum wind drift on a single building. It's a little conservative, but usually ends up with a 2" joint or less. The first time I tried to set the expansion joint wide enough to accommodate the seismic drift of both buildings my boss looked at me cross-eyed and said we don't do that because it results in unrealistically wide joints (this particular 8 story building would have had a 7" expansion joint).

 

[BOCH]

this is true "lion06", in seismic zones displacement due to earthquake shall be multiplied by 0.7xR befor doing the SRSS operation and this will give you wide joints (around 15 to 20 cm and more)

 

[Galambos]

Lion06, so glad you said that because I have across this reasoning before, too. It's primarily the reason I asked, although I can't find justification for it.