Existing Building Drift for New Expansion Joint

[mck26]

Designing a building addition in New York State. The addition will be structurally separate. The existing 2 story building does not have any obvious lateral resistance shown in existing drawings. Only thought is the exterior masonry walls help provide lateral resistance. How do I approximate a building drift to calculate the required expansion joint size?

 

[EngineeringEric]

Are there any significant signs of drift/deflection cracking? if the structure is old and has seen near design wind and EQ loads and does not show cracking/movement than it would be fair to assume a deflection limit of the material (L/600 style). So take that as the maximum of existing and your new drift and add them together (1" for old & 0.75" new = 1.75" of expected movement) then add a nice factor for safety, say .75% of old and .33% of new... use your judgment.

Or you can push test it! stiffness is equal to force / deflection

 

[KootK]

Great question. I've often wondered the same thing. From what I've seen, people handle this one of two ways:

1) Attempt to calculate the drift of the adjacent building. I almost never see this done in any rigorous fashion as folks rarely have the fee for it.
2) Assume that the existing building was designed to meet the drift limitations of its day. As always, assumptions can be dangerous.

While it's reasonable to assume that an older building may have already seen its design wind force, that will rarely be the case for seismic loads. The vast majority of buildings will be utterly untested seismically.


The greatest trick that bond stress ever pulled was convincing the world it didn't exist.