DEC 8 Changes
jim moore
document and most recently was successful to call out roof purlins in
screen enclosures to bear a 300# point load. With this said I have
read postings referencing .070 to an .090. I have spoke to all our
major suppliers who have no specific answers. Some suppliers have
indicated .050 nomin al and others .050 minimum. There are also
difference amongst different engineers. If the AAF is so proactive and
concerned of the quality of structures and the accuracy of engineering,
I strongly suggest the powers to come to a concensus and produce
something in writing for the suppliers in order to have the proper
material available for shipment come December 8th. Now some of you may
say well Jimmy if you were at the meetings you would know and you are
correct, but as of today according to my suppliers, they are not even
sure. Thanks in advance for everyone involved in the process and
please get everyone, especially the suppliers on the same page. This
is the least the AAF can do for the suppliers for they are always there
to support.
David W Miller
Here is a comparison between the 12" distributed load and the 300# point
load and associated moments. As one would expect the differences diminish as
the span increases.
David Miller
-----Original Message-----
From: Aluminum-Struct...@googlegroups.com
[mailto:Aluminum-Struct...@googlegroups.com] On Behalf Of Steve
Sincere
Sent: Sunday, November 12, 2006 11:19 AM
To: Aluminum Structure Contractors
Subject: Re: DEC 8 Changes
Jim,
For what it is worth, here are my answers on allowable span for
existing extrusions based on the 300 lb point load
Extrusion Allowable Span
2X4 SMB 8' 3"
2X4X.045 SNAP SMB 9' 0"
2X5 SMB 13' 8"
2X6 SMB 20' 5"
2X7 SMB 26' 3"
2X8 SMB 47' 1"
2X9L SMB 51' 8"
2X9H SMB 55' 1"
2X10 SMB 61' 4"
2X2X.045 3' 10"
2X3X.045 6' 4"
2X3X.045 + 1X2 SNAP 4' 6"
2X4X.050 10' 5"
2X2X.090 7' 0"
3X3X.090 16' 1"
3X2X.050 + 1X3 SNAP 9' 5"
3X2X.070 + 1X3 SNAP 10' 11"
These values are based ONLY on the 300 pound load at a single point as
opposed to being distributed over one foot, so they are slightly
conservative. The spans were determined using the ADM criteria for
major axis bending and assuming simply supported end conditions.
You will notice that it takes a substantial member to span over 8 feet
(in the case of purlins and eave rails) and even more so when spanning
over 11 feet (in the case of roof bracing). I expect there will be new
extrusions coming to market to address this, but I don't think they
will arrive by December 8th.
I hope this helps to get the ball rolling.
Steve Sincere
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Tarnowski
The 300# point load does not apply to the roof bracing based on the
final code determination that roof bracing was not clasified as a
primary member.
Gus
Tarnowski
"PRIMARY MEMBER. Structural framing members providing structural
support to other members and/or surfaces of a structure including, but
not limited to beams, posts, columns, joists, structural gutters,
headers, purlins etc. "
Gus Tarnowski
James Moore
this correct or a miss print. thanks
Tarnowski
did you get my private email that I sent you with the attached full
code changes? I did not get a response.
anyway lets not all get caught up on this 300lb point load in 140mph
zones, the new wind loads will control.
the 300lb point load effects the people in the 110 and 120 mph zones
more.
for the 140mph exp B zones here are my "notes" to compare for the eave
rail based on 21psf wall load combined with the 6psf roof load:
neglecting the 1x2 or 1x3 and for 6063 -T6 alloy
extrusion allowable span
2x3x.050 4.1'
2x3x.065 6.2'
2x3x .070 7.3'
2x3x .090 8.3'
3x2x .050 4.8'
3x2x .065 6.0'
3x2x .070 6.5'
3x3x .060 7.2'
3x3x .072 8.4'
3x3x .090 9.7'
Gus Tarnowski