Need a book? Engineering books recommendations...

Return to index: [Subject] [Thread] [Date] [Author]

RE: Rigid frame deflections (again)

[Subject Prev][Subject Next][Thread Prev][Thread Next]
Once you had the frame forces, couldn't you solve the frame drift by virtual work by placing a unit load at the top of the frame and solving in terms of L, h, Icol and Ibeam?

Bill Allen

-----Original Message-----
From:	James F Fulton [SMTP:James_F_Fulton(--nospam--at)]
Sent:	Monday, January 26, 1998 5:45 AM
To:	seaoc(--nospam--at)
Subject:	Re: Rigid frame deflections (again)


______________________________ Forward Header __________________________________
Subject: Re: Rigid frame deflections (again)
Author:  James F Fulton at CCMCED01
Date:    1/22/98 3:37 PM

Kate, when you asked the questions earlier this month, some responses 
indicated that you could refer to Kleinlogel's book and find formulas for 
rigid frame DEFLECTIONS.  I've got a copy of the 2nd American Edtion, Second 
Printing (1964), and in that edition at least, there are only equations for 
frame forces and moments--no deflections. I looked in a couple of other 
references on my shelf (incl Roark) and can find no DEFLECTION formulas for 
rigid frames. I would be interested in knowing if and where others find 
deflection formulas for rigid frames.

I've got a copy of the Interchange article, and I used slope-deflection 
theory to derive the equation given there for the pinned=end frame. However, 
based on my derivation, the equation in Interchange is incorrect in that the 
factor in the denominator times Ibm should be "1" , not "2", which 
incidentally is what you quoted in your original note.  (You remember, the 
one where you did not want to use a "fancy shmancy" $$ computer program for 
these "small and uncomplicated" frames)  Well, it looks to me that 
defermining frame deflections, as opposed to forces and moments, for even 
simple rigid frames is not trivial and there does not appear to much 
information (equations) for these structures in the texts either. So a 
computer program appears to be the way to go, even for a statically 
determinant frame, if one's interest include deflections. 

______________________________ Reply Separator _________________________________
Subject: Rigid frame deflections (again)
Author:  seaoc(--nospam--at) at Internet 
Date:    1/21/98 7:35 PM

Guys and Dolls:

Now that I have the Steel Interchange sheet from Modern Steel Construction 
(4/93) which shows the quick hand-calc for rigid frame defelction, I have 
started using it.

HOWEVER, I have noticed something very odd. Extremeley odd.

The formulas for pinned and fixed bases follow (and please excuse the 
crummy formatting):

        drift = P*H(squared)/6E  *(H/Icol + L/2Ibm) 
        where    P = load
                H= height of frame
                L=span of frame
                Icol= I of column
                Ibm= I of beam

For fixed-at-base frames:

        drfit=P*H(cubed)/12EIcol * (3K+2/6K+1)

        where   K= Ibm*H/Icol*L
                everything else as above

Now here is the strange part. I have two frames along line D in my project. 
One has a 17 foot span and the other a 7 foot span (L). Both of  them are 
10.5 feet high (H).  And  I am assuming:

P = 1 kip for each frame  (just getting relative rigidities at this point). 
Relative rigidity R is the inverse of the drift; i.e. 1/drift

For both fixed and pinned at base calcs, my 7 foot long frame is stiffer 
than my 17 foot one.

I have hunted HARD for errors in my calcs and I can't find any. I have done 
the calc both by hand and with a spreadsheet and I still get the same 
answer: the tall skinny frame is stiffer than the short fat one.

I do not buy this. Has anyone else had this problem? Is it me? Is it the 

Kate O'Brien
Simi Valley, CA

RFC822 message headers.txt >>