Need a book? Engineering books recommendations...
RE: Unreinforced Masonry Wall from 1965[Subject Prev][Subject Next][Thread Prev][Thread Next]
- To: <seaint(--nospam--at)seaint.org>
- Subject: RE: Unreinforced Masonry Wall from 1965
- From: Harold Sprague <spraguehope(--nospam--at)hotmail.com>
- Date: Fri, 18 Nov 2011 15:44:45 -0600
With walls that tall and not designed well, expect problems at the roof attachment also. Using girts to support the masonry at mid-span is a good solution. But I would still check the connections.
Regards, Harold Sprague
Date: Fri, 18 Nov 2011 08:13:08 -0800
Subject: Re: Unreinforced Masonry Wall from 1965
Thanks for your detailed and helpful response. Airbag testing is a great idea, but does not seem practical for 38'x27' panels which would have to be tested in both directions due to the multi-wyth construction. Arching action (as suggested by Brian Felker) won't help in all panels because the supports are not rigid enough (roof purlins, corner columns). It looks as if mid-height horizontal beams carrying wind load to steel columns will be the best solution. The architect and owner are already aware that we're going this direction, but I wanted to exhaust the other possibilities first.
Thanks also to everyone else who responded.
From: Harold Sprague <spraguehope(--nospam--at)hotmail.com>
Sent: Wednesday, November 16, 2011 3:12 PM
Subject: RE: Unreinforced Masonry Wall from 1965
Back in 1965, and depending on the project location, walls often were NOT designed for lateral loads. In many areas of the country lateral loads were not designed for many buildings. In the relative early days, a lot of architects and engineers would use the empirical method of "designing" masonry. Many architects and engineers would count the brick as part of the wall and would use the empirical ratios in the UBC. They would also count the air space between the 8" wall 4" brick facing. Therefore an 8" wall with 4" brick and a 2" air space was treated as a 14" wall.
The issue came to a head in the 1970's when we started to insulate walls. This was a departure from the integral masonry and the building components were separated for thermal reasons. Historically, plaster knitted a lot of components together whether structurally intentional or not.
Per UBC 1970:
Table I in the 1970 UBC allowed a URM exterior unreinforced wall to have a h/t ratio of 20. If you had any reinforcing you could go to 30. If the wall was interior, the ratios were 36 and 48.
I lost a client many years ago because I could not get the numbers to work. The client found an engineer who said the walls were OK using the overall wall thickness of a cavity wall and allowed for the empirical method. A wind storm blew the walls down some years ago. No one was hurt.
One approach is to do a test with an air bag. Put the wind force on the wall and test it. I doubt it will work, but it might. Anchorage at the top is another major issue. It is not likely to work.
To rehab the wall, you can strong back the wall with structural steel at intervals that allow the CMU to span horizontally. And use post installed anchors to resist the suction loads.
Regards, Harold Sprague
On Mon, Nov 14, 2011 at 2:05 PM, Daniel Popp <drp181(--nospam--at)yahoo.com> wrote:
David Topete, SE
- Prev by Subject: Re: Unreinforced Masonry Wall from 1965
- Next by Subject: Update and News from Vish
- Previous by thread: Re: Unreinforced Masonry Wall from 1965
- Next by thread: Re: Unreinforced Masonry Wall from 1965