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RE: k for compression members of frames with sidesway

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        The documentation is skimpy on this but if you look in SEAOC Blue Book (C105.2 page 105) you will see that a glimpse of an explanation
        (the factor described here is basically an attempt to incorporate P-Delta effects)
        The following paragraph is also telling (That the P-delta effects might be more significant in lower seismic areas 
         Francois Rambau
         Star Building Systems     
-----Original Message-----
From: Daryl Richardson [mailto:h.d.richardson(--nospam--at)]
Sent: Saturday, September 28, 2002 12:10 PM
To: seaint(--nospam--at)
Subject: Re: k for compression members of frames with sidesway


        It is also my understanding that the k factor can become 1.0 and furthermore that the amplification factor 1/(1-Cf/Ce) also becomes 1.0 in the unity check equations if a P-delta analysis is performed.

        That said, you also have some other alternatives to assist you with the design.  Perhaps you can actually consider the base fixed; your codes allow a 1/3 increase in stresses, etc., which may allow you to develop (or consider) fixity even if the foundation was originally only designed for axial load.  What about bracing the bent?  Even a single horizontal strut (if it can resist moment) can reduce the actual length.  Perhaps you can provide horizontal bracing in the supported structure and thereby transfer some of the wind loading away from the critical bent to another part of the structure.

        I hope these comments are helpful.


H. Daryl Richardson

Ken Peoples wrote:

I am trying to justify using a lower k value than 1.5 for a frame subjected to sidesway.  The condition is a two column bent for conveyor trusses.  The columns are inclined round pipes with no intermediate bracing and a hammerhead on top for the trusses to connect to.  I am examining the capacity with wind moments perpendicular to the truss centerline. Page 5-135 of the AISC 9th edition indicates that a design value of 1.5 for condition (f) would "generally be conservative". The Canadian Institute of Steel Construction  - Handbook of Steel Construction 5th Edition Section 9.3.2 indicates "The effective length factor, K, shall be taken as 1.0 for compression members of frames (a) in which sway effects have been included in the analysis used to determine the moments and forces....." I think this is saying that if I include P-delta effects in my analysis that I can use k=1.0 (please correct me if I am not interpreting this correctly). What I would like to know is whether there might be similar wording somewhere in AISC. As always, thanks in advance for your help. Best regards, Ken Kenneth S. Peoples, P. E.
Lehigh Valley Technical Associates
1584 Weaversville Road
Northampton, PA 18067-9039
Phone: (610) 262-6345
Fax: (610) 262-8188
e-mail: kpeoples(--nospam--at)