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Seismic Joint for bridge in residential wood structure

Seismic Joint for bridge in residential wood structure

Seismic Joint for bridge in residential wood structure

I am designing a 3 story, single family structure out of wood and the client wants a 12' weather tight bridge at the second floor level to connect to an existing 2 story structure. Does anyone know of a method of seismic isolation that would not expose the climate controlled interior conditions to exterior weather?

RE: Seismic Joint for bridge in residential wood structure

If the aim is to simply keep a weather tight seal under regular service conditions, but allow the buildings to move independently in the event of an earthquake, then it just requires designing in a structural fuse (a weak point in the link between the buildings) that doesn't result in the collapse of the bridge. The structural supports will need to be able to move enough to accommodate the expected relative displacement of the buildings, without moving off of the what they bear on.

If you want it survive the earthquake and still be weathertight afterwards, things get much more difficult (and expensive). For that, you'll need some sort of expansion joint, such as an anchored elastomeric seal.

RE: Seismic Joint for bridge in residential wood structure

It's actually to isolate the structures for wind loading as I'm in New England so I do need it survive the storm. Maybe not the big one, but a good size one. Do you have any specific product you use that you could share a link to? My only other option is to design the floor of this bridge to resist the full load of the shear forces.

RE: Seismic Joint for bridge in residential wood structure

For that, I might not be the best source. Anything I'm familiar with along those lines would be massive overkill for your situation. I suggest looking at what is used for pedestrian skywalks between commercial buildings. Even that might be overkill for residential wood construction.

RE: Seismic Joint for bridge in residential wood structure

I'd try like the devil to get away without a movement joint. Can you share a plan so that we can get a sense of the thing? One benefit of it being all sealed up is that you ought not have to worry about post-construction, temperature strains.

RE: Seismic Joint for bridge in residential wood structure

Here are the plans from the owner. The bridge is shown in the 2nd floor plan, right side elevation, rear partial elevation, roof plan, and left side elevation.

One thought I had to avoid a movement joint is to lap the LVL bridge beams with LVL's in the floor framing then utilize the floor diaphragm to distribute the forces to the shear walls. I was going to use the shear value from the smaller building instead of the larger one since resisting the lesser of the two loads will at least keep the two structures moving in unison with out blowing the connections over the top.

RE: Seismic Joint for bridge in residential wood structure

Thanks. I did one last month where the "bridge" was the full width of the building which obviously feels a bit better. That said, I'd still go with hard connections either end. Get some healthy drag struts coming in off the bridge into the main building if you can. As you know, accurately predicting behavior for wood lateral isn't a very exact science. So I wouldn't get to bogged down with this. Just some reasonable estimate of what it might take to keep the two things stitched together in a high wind.

RE: Seismic Joint for bridge in residential wood structure

I would want to avoid a joint. It looks like the bridge will be conditioned and also of a length that thermal movements will be not very significant.

RE: Seismic Joint for bridge in residential wood structure

Thanks for the helpful feedback.

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