Need a book? Engineering books recommendations...

Return to index: [Subject] [Thread] [Date] [Author]

RE: New wood floor in existing masonry building - ties required at 4' oc?

[Subject Prev][Subject Next][Thread Prev][Thread Next]
Title: Message
Michael:
 
The furred walls are used for insulation and gravity support only.

It was my understanding that the code provision was to prevent masonry walls from pulling away and collapsing.  The engineer is arguing that the existing roof is designed to accomplish the task of keeping the walls from collapsing out of plane. 
 
I told him I understood his point but there is a compatibility issue and if the wall pulls away from the floor and the wall is intended to brace the floor then there is a problem.
 
Respectfully,
Scott
-----Original Message-----
From: Mlcse(--nospam--at)aol.com [mailto:Mlcse(--nospam--at)aol.com]
Sent: Saturday, July 17, 2004 6:39 PM
To: seaint(--nospam--at)seaint.org
Subject: Re: New wood floor in existing masonry building - ties required at 4' oc?

Scott,
 
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:
Scott: I would say no.  The 2nd floor is dependent upon the wall for support, not the wall on the 2nd floor.  WRT you your email on vehicle impact, UBC/IBC requirements protect the driver  not the barrier.  I think that this was added resultant to an accident in a Seattle parking garage. 
----- Original Message -----
Sent: Saturday, July 17, 2004 6:18 PM
Subject: New wood floor in existing masonry building - ties required at 4' oc?

Anyone:

IBC 1604.8.2 and IBC 1620.1.7 and IBC 1620.2.1  prescribe that masonry and concrete walls shall be anchored to floors and roofs that provide out-of-plane support. The code indicates ties at 4 feet maximum and that wood ledgers cannot be used in cross grain bending.

I have a situation where a new second floor is being built inside an existing masonry building.  The floor framing is supported on new interior stud walls and on furred out stud walls installed around the interior side of the exterior masonry walls.  The new second floor diaphragm is braced by the existing exterior masonry walls.  The connection to the existing walls is a bolted ledger and there are none of the prescriptive perpendicular anchorage ties provided.

Does the code require the ties for this condition? The roof appears to be already designed to brace the top of the existing masonry walls.

Thanks.

Scott M. Haan P.E.
Deputy Building Official