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Re: URM - Parapet Bracing Question -Reply

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Dennis S. Wish wrote:

> 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?

Yes. The cap flashing needs to be in good shape or else solutions such as
replacing the capor concrete cap can be used.

> 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