Design a Building with Expansion Joints 1

[StructuralAddict]

Hello Everyone,

I am designing a basic two-storey building (moment resisting frame) that spans about 120 meters along one direction and 50 meters along the other direction. I know that in such large spans, we should provide expansion joints in the building.

Regarding the expansion joint, does it split the slab only? Or do I need to split the entire frames as well?

In other words, do I need to design each part of the building separated by the expansion joint individually? (Designing different frames separately that look like one building because they are very close to each others).

I appreciate if you could share your experience with me

 

[JAE]

120 meters (about 400 ft) may not need an expansion joint depending on the framing and how you handle cladding, etc.

If there is an expansion joint - you either have to create essentially two separate buildings with twin columns at the joint, or design beam connections at the joint that allow horizontal slip movement.
This would include everything such as slabs, beams, walls, exterior cladding, plumbing, conduit, etc.

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[StructuralAddict]

Thank you very much JAE for your clear explanation!
As a follow up to your answer: If I create two separate buildings with twin columns at the joint, then does this mean that I will model each frame individually in ETABS? Will this affect the way I input the wind load and seismic load?

 

[JAE]

Yes - two separate structures. Not sure how ETABS can respond to this - perhaps it can handle both sections in the same model - some software cannot.

For wind loads you would treat the exterior wind pressures the same as if you had one building except that the internal wind pressures will now act separately on two structures.
This can definitely affect your main wind force resisting system winds and how they are applied to the structure.

If one structure, the internal wind pressures sort of cancel each other out horizontally. With an expansion joint they don't.

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[JasonMcKee71]

You should create two, independent models in Etabs. The behaviour of each one can be much different compared to the other one. Moreover, you shall check the joint width so that the buildings do not collide under horizontal loads, eg. quake.

Jason McKee
proud R&D Manager of
Cross Section Analysis & Design
Software for the structural design of cross sections
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[thaidavid40]

In addition to the thermal separation distance, be sure to allow for the seismic separation distance needed also. This is at least equal to the square root of the sum of the squares of the individual building displacements.
Dave

Thaidavid

 

[BUGGAR]

The structure has a diaphragm ratio of less than 3:1. I would vote for no joints in the structure unless required by geotechnical considerations. Let the Architect figure out his joints.