Expansion Joint size to accommodate wind drifts

[VA-Struct-Engr]

Hello, I posted this question under "Moment Frame & Shear Wall engineering Forum" but got no responses (thread726-498488), so am re-posting here, hoping to get some help.

I am designing a 10 story CFS building in the mid-Atlantic region. I have to have an expansion joint in the building as the footprint is large. Building is SDC A.
When sizing the expansion joint, should I take building drift due to wind into account? Both structures use flat strap braced frames as the lateral force resisting system, however, the structures are of different shapes. Should I be concerned about the structures banging into each other if subjected to wind loads?

Follow up question: If I have to take wind drifts into account, I will treat it as a serviceability issue, designing for 10 year MRI wind speed and limiting building drift to H/500 of the overall building height. Each structure will move ~2.5in at roof level. Using Square root of sum of squares, I will need a 4" (rounded up from 3.5") expansion joint. Does this seem reasonable? What is typically done at these situations.

Thank you for your responses in advance.

 

[dik]

There may be local code requirements about the size of the joint based on the movement anticipated, maybe with a factor of 2x or 3x the movement. To achieve such a large 'gap' you likely have to use overlapping steel plates. You can increase the bracing to minimise the deflection a bit. If all interior, you may be able to minimise the number of joints since thermal movement, other than that at construction will be greatly reduced.

So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[BridgeSmith]

If both structures have about the same lateral stiffness for wind load, so that they move approximately the same amount under the same wind, and presumably they'd be moving in the same direction, the differential movement that would have to be accommodated by the expansion joints would be fairly small, wouldn't it?

Rod Smith, P.E., The artist formerly known as HotRod10

 

[EZBuilding]

If both structures have about the same lateral stiffness for wind load, so that they move approximately the same amount under the same wind, and presumably they'd be moving in the same direction, the differential movement that would have to be accommodated by the expansion joints would be fairly small, wouldn't it?

This would assume that both buildings have the same natural frequency and that the wind event occurs simultaneously to both structures. It also assumes that the wind magnitude on both buildings are equivalent, but may be different as one is being impacted by windward where as the other leeward pressures. The OP mentions the structures as being of different shapes so I don't think we can make these assumptions.

I would be leery about using a 10 year MRI event for the sizing of the expansion joint. What are the ramifications of the buildings banging into each other during a strength event?

 

[XR250]

Geez - 10 story?
I hope this ain't your first rodeo. I am not sure how you could even calculate the drift on a CFS building of that height as the slack in the straps and connections will have to be taken up before any elastic behavior occurs. Fortunately, the sheetrock will likely engage first
I watched the construction of an 8 story CFS hotel a few years ago. Thee amount of straps, connections and heavy gage studs was mind- boggling. I could not see how that was more efficient than using red iron in terms of cost and reliability.

 

[BridgeSmith]

This would assume that both buildings have the same natural frequency and that the wind event occurs simultaneously to both structures. It also assumes that the wind magnitude on both buildings are equivalent, but may be different as one is being impacted by windward where as the other leeward pressures. The OP mentions the structures as being of different shapes so I don't think we can make these assumptions.

Good points, especially about the natural frequency. The OP posted the story drift as being the same, so to me, that would indicate similar stiffness and therefore natural frequency, but if the stiffnesses are different, the buildings could oscillate differently, even if the wind can assumed to be approximately the same magnitude and from the same direction.

Rod Smith, P.E., The artist formerly known as HotRod10