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RE: URM - Parapet Bracing Question -Reply

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Barry, I'm not sure I follow your second condition. The first is typical of
most braces. I mount a 4x3x18" long angle to the roof and secure it to
blocking or rafters (depending upon parallel or perpendicular framing
conditions) with sufficient wood screws (pre-drilled) to accomodate the load
to the brace of 0.3Wp. The connection to the parapet can be done a couple of
ways, however, in my example, I use a 4x6x6" angle wraped over the concrete
parapet cap and epoxied down into the cap with a threaded rod, washer and
nut. To the parapet secured angle is welded a plate drilled to accept a
2-1/2" x 2-1/2" x 1/4" angle brace which is connected to both angles with a
threaded machine bolt, washer and nut. The brace is sloped 2:1 with the
roof.
In your second example, are you securing a continuous angle ledger to the
urm parapet and tieing it back to the roof at greater than 6' spacing?
BTW, in the analysis for the brace, the unbraced height is assumed to be
from the center line of the tension anchor at the roof diaphragm to the top
of parapet.

Dennis Wish PE

|-----Original Message-----
|From: Barry H. Welliver [mailto:wellive(--nospam--at)ibm.net]
|Sent: Saturday, February 21, 1998 7:29 AM
|To: seaoc(--nospam--at)seaoc.org
|Subject: Re: URM - Parapet Bracing Question -Reply
|
|
|If (when) the roof anchors are required, a good way to acheive such is to
|surface mount a flat strap or angle on the roof sheathing perpendicular to
the
|parapet and use this as the connection for a diagonal brace also. This
would of
|course require roof work at these locations. This scheme places the braces
for
|parapets at approx.6 ft. I think another acceptable means to "capture" the
|parapet is to run an angle over the outside edge and fasten this to the
braces.
|I think I've done this (with a sufficiently stiff top angle) where I've
spaced
|the braces at 10 to 11 ft (2x5'-4").
|
|Barry Welliver
|
|Dennis S. Wish wrote:
|
|> Thanks Tim, at one time there was an allowance to exceed the 6'-0"
spacing
|> for concrete capped parapet. This must have died some years ago in place
of
|> the 6'-0" max spacing.
|> Thanks again for the reply
|>
|> Dennis Wish PE
|>
|> |-----Original Message-----
|> |From: Tim McCormick [mailto:TMCCORMI(--nospam--at)BAS.CI.LA.CA.US]
|> |Sent: Friday, February 20, 1998 1:43 PM
|> |To: seaoc(--nospam--at)seaoc.org
|> |Subject: URM - Parapet Bracing Question -Reply
|> |
|> |
|> |Dennis,
|> |
|> |My copy of 1994 UCBC Appendix 1 does not have the 10 foot rule for
|> |parapets. Anchors are generally limited to 6 feet but this could be
|> strictly
|> |interpreted to mean only the diaphragm anchorage as written. The actual
|> |language is given below. By the way, I get these quick code quotes off
|> |my ICBO CODE EXPRESS CD  I think this is a great tool for quickly
finding
|> |code requirements from all of the uniform codes. Here's the section:
|> |
|> | A113.6 Parapets. Parapets and exterior wall appendages not
|> |conforming to this chapter shall be removed, or stabilized or braced to
|> |ensure that the parapets and appendages remain in their original
position.
|> |The maximum height of an unbraced unreinforced masonry parapet
|> |above the lower of either the level of tension anchors or roof sheathing
|> |shall not exceed the height-to-thickness ratio shown in Table A-1-F. If
|> |the required parapet height exceeds this maximum height, a bracing
|> |system designed for the forces determined in accordance with Chapter
|> |16 of the Building Code shall support the top of the parapet. Parapet
|> |corrective work must be performed in conjunction with the installation
of
|> |tension roof anchors. The minimum height of a parapet above any wall
|> |anchor shall be 12 inches (305 mm).
|> |EXCEPTION: If a reinforced concrete beam is provided at the top of the
|> |wall, the minimum height above the wall anchor may be 6 inches .
|> |
|> |Literally, this means its up to the design but I have seen most URM
|> |parapet braces spaced at six feet.
|> |
|> |Hop this helps,
|> |
|> |Tim McCormick, P.E.
|> |City of Los Angeles
|> |
|> |
|> |
|>
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