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RE: Sign Post Design, K-Factor and L/300 Criteria

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Daniel,

Where did the L/300 deflection criteria come from.  Cantilever signs, light
poles, etc. usually don't have tight deflection criteria.  Remember recent
news footage of light poles really dancing in the breeze in our recent
hurricanes.
Also, usually p-delta doesn't control since the bending is far more
significant then the axial, although if your scoreboard is heavy p-delta
might have to be considered.

Bob G.

-----Original Message-----
From: Daniel Boltz [mailto:dboltz(--nospam--at)1st.net]
Sent: Thursday, September 23, 2004 9:26 AM
To: seaint(--nospam--at)seaint.org
Subject: Sign Post Design, K-Factor and L/300 Criteria


I'm designing a column that supports a scoreboard.  My deflection criteria
is L/300.  I'm using a K-Factor of 2.10 per AISC Fixed-Free boundary
conditions.  I'm a little unsure of how to calculate the deflection criteria
for the sign.      

I have a deflection at the top of 1.72".  The bottom of the sign is 10' off
the ground and the sign is 12.13' tall.  If I just use the full length of
the column (L=265.56"), then I have L/deflection = 265.56/1.72 = 155.  

1.  Should I be using relative deflection to compare to the L/300 criteria?
My relative deflection between the top and bottom of the sign is 1.22".  For
the full column length, this would result in L/218 and for the length/height
of the sign I would have L/119. 

2.  So do I use the full length of 265.56"/1.22" = 218 or use the
length/height of the sign which equals L/119?  The height of the sign is
145.56" and would result in 145.56/1.22 = 119.  Neither is close to the
required deflection criteria.

Thanks.   




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