Force transfer across building expansion joint

[WWTEng]

Consider an existing 40-50 year old construction with a proposed new addition to its two sides. The new addition is large enough to warrant use of an expansion joint between the two buildings (new and existing). I have worked on few projects like this and never considered transferring any lateral or vertical forces across the expansion joist as I always thought that this was the conventional approach.

But is it advisable/possible to transfer lateral forces from new to the existing across the expansion joint? The new addition is as tall or less than the existing and the governing lateral force is wind. The existing building already has a lateral system designed for these forces and the idea would be to save some cost by not providing a new lateral system.

 

[frv]

Provided the existing building can handle the additional lateral forces, it can be done. You will require special detailing- pay attention to allowing movement in one or two directions, as required. For example, you could use an edge angle with a vertically slotted hole (to allow gravity movement), where the attachment to the new building is a bolt attached through the slot, but where the head is offset from the angle (to allow for "expansion joint" movement between the buildings).

Obviously, you's have to look carefully at the bolt connection to the existing structure, but I've done similar things in the past. I'd highly recommend inspecting these elements during construction- something that can easily be screwed up in the field.

 

[steellion]

If you are transferring new forces to the existing building, my understanding is then you then need to analyze the entire structure (new and existing) against the current code. The IBC allows a 5% load increase without re-analysis, but that's it. The 40-50 year old structure may not meet the current code and would then need to be retrofit. Usually, it's easier to keep the structures totally independent, as you have noted above.

 

[briancpotter]

I assume the intent is something like this:

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Where you have wind blowing "into" the new addition instead of the existing building, and you want to transfer this lateral force into the existing building. The problem is that this is precisely the direction that needs to be free from restraint to prevent damage from thermal expansion.

Brian C Potter, PE

http://simplesupports.wordpress.com

 

[hokie66]

The "conventional" approach is the best approach. You can design one building to lean on another, but at some stage, the 50 year old building reaches the end of its life and is demolished. What then?