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Re: New wood floor in existing masonry building - ties required at 4' oc?[Subject Prev][Subject Next][Thread Prev][Thread Next]
- To: seaint(--nospam--at)seaint.org
- Subject: Re: New wood floor in existing masonry building - ties required at 4' oc?
- From: Mlcse(--nospam--at)aol.com
- Date: Sat, 17 Jul 2004 22:39:26 EDT
If you are using the existing masonry walls for lateral bracing of the new second floor (as shear walls), then you need to tie the walls in the out-of-plane direction to this new second floor. The mass of the new second floor is additive to the existing buildings mass. As soon as you attach to the existing walls, you need to comply with the wall anchorage requirements. Can the existing masonry wall resist the additional seismic forces from the new second floor weight, let alone the existing roof wall anchorages for the new additional seismic force being distributed to the roof above?.
Placing furring studs under the floor joist at the masonry perimeter wall takes the vertical load, but you still have a horizontal load to transfer into the existing masonry wall. If the wall moves out of plan, the wood ledger could/will go into cross grain bending, therefore the need to anchor the new floor/wall in the out-of-plane direction. You need to protect the ledger from cross -grain bending so when the seismic force change directions and act parallel to the perimeter wall, you can still transfer diaphragm shear forces to the CMU wall since you haven't failed the ledger.
If you build a box within a box, the new second floor has a totally independant lateral resisting system, and is not attached to the existing building walls, therefore no need to provide wall anchorages. As soon as you attach to the building walls you have a deformation compatibility issue. When the existing wall deflects out-of-plane at mid-height (during an earthquake) they will impose a load on the new second floor unless there is seismic gap between the existing building and the new independant second floor.
You can space the wall anchorage furthur than 4 feet, but then you have to show that the wall can span horizontally at the floor line between the anchorages.
Michael Cochran S.E.
In a message dated 7/17/2004 6:39:08 PM Pacific Standard Time, shapton(--nospam--at)nwlink.com writes:
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