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Re: Minimum Eccentricity for Steel Column (Last question of 2015?)

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Thank you for your comment Paul.
By P/180 I'm assuming you refer to the P Axial load of the column, right?

J.E.
________________________________________
From: seaint-seaosc(--nospam--at)mail-list.com <seaint-seaosc(--nospam--at)mail-list.com> on behalf 
of Paul Ransom <PRansom(--nospam--at)PaulRansom.ca> Sent: Wednesday, December 30, 2015 
6:12 AM To: seaint-seaosc(--nospam--at)mail-list.com
Subject: Re: [SEAINT-SEAOSC] Minimum Eccentricity for Steel Column (Last 
question of 2015?)

Jim,

The steel design standards typically suggest h/400+ and may provide an upper 
 limit before a more explicit stability analysis with as-built offsets is
required. Keeping a load within the "kernel" (+/- width/6) of the base is
not a bad rule of thumb for human-scale wood beam and post construction but
there are no limit conditions to that type of rule-of-thumb.

In this case, the eccentricity is h/180. A simple pin-pin post is probably
fine with this offset if the top/bottom connections can tolerate it
including local bearing. However, this will create a stability load P/180
per post  (e.g. cumulative) that has probably not been included in the
lateral brace load path.

If you have moment connections OR if the pin connections can respond like
fixed connections over the range of loading, then you will need to check the 
 posts for beam-column conditions due to the added flexure. If this is the
condition and you currently have 1" offset, that means that they have
already pulled the structure back towards column alignment (e.g. the
misalignment is something larger than 1").

At the very least, consider the influence of sum(P/180) to connecting
elements, connections and the lateral force resisting system. This is
back-of-the-envelope quick calculation.

Regards

Paul Ransom, P.Eng.

Paul Ransom Engineering

> Date: Wed, 30 Dec 2015 03:42:41 +0000

> From: Jim Edwards <jimedwards93216(--nospam--at)outlook.com>

> Subject: Minimum Eccentricity for Steel Column (Last question of 2015?)

> 

> Happy New Year to all structural engineers.

> 

> Here is my last day of the 2015's question(?):

> 

> I think in Wood Design we take the (width of the column)/6 as the minimum

> eccentricity.  This is the case when there is absolutely no eccentric
loading

> and the load it concentric.

> 

> how about steel columns?

> 

> I have a scenario where the some existing 15 feet tall pipe steel columns

> are 1 inch out of plumb..

> 

> This means at the present time these column are taking an additional 1
inch

> of eccentricity over their original design.

> 

> The pipes are 8 inches in Diameter.

> 

> if I establish that the 1 inch out of plum is not within acceptable
construction

> tolerance, then I'd have to evaluate these column to check their
strength.

> In that Case if they are overstressed, I have to reinforce them.

> 

> Your fellow structural engineers' comment are greatly appreciated.

> 

> Jim Edwards

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