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RE: Column Design
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- Subject: RE: Column Design
- From: "David Maynard" <davemaynard(--nospam--at)vcn.com>
- Date: Thu, 29 Dec 2005 07:56:39 -0700
- Disposition-notification-to: "David Maynard" <davemaynard(--nospam--at)vcn.com>
OK, if I get this correctly, what you are saying is that you are getting your maximum axial load at one location, your maximum strong axis bending at a different location, and your weak axis bending at another location. So, three loading considerations all at different points along the length of the member, and you want to know which one to design for??? That's simple. Check them all. At each location, one loading situation is at a max and the other two are there, but to a lesser degree then somewhere else. So, what you will end up with is three separate loading combinations that will look something like this: Location A: P = Max Mx = magnitude at location My = magnitude at location Location B: P = magnitude at location Mx = Max My = magnitude at location Location C: P = magnitude at location Mx = magnitude at location My = Max You check all of these load scenarios for your member with the appropriate design parameters (unbraced lengths, K values, and what have you), and look at them all as beam-column interaction. If all combinations are acceptable, then you have successfully designed your member. If one combination fails, then you obviously have to do a little more looking around. Implementation of a spreadsheet would work very well in a case like this. I have used STAAD in the past for analysis and applied my own design using the results. Within STAAD, and arguably one of the most powerful tools for me, is an input called "Beam Force Summary." This output will give the user all of the maximums and minimums along the beam length, or a group of beams, at the specific location. Along with that maximum, it will give the corresponding loads at that point as well. It makes getting the loads from my analysis a lot more efficient with way less headaches. Now, if you want to take a conservative approach to it, you could take the maximum axial, strong axis and weak axis bending, and design a section based on those, with design parameters indicating the maximum unbraced length, conservative K-values, and Lx and Ly at a maximum for the length. With doing this, your section will definitely be on the conservative side and can likely be standardized where you feel applicable. I hope this helps in answering your situation. David Maynard, PE Gillette, Wyoming -----Original Message----- From: Santhosh Kumar Yedidi [mailto:sant527(--nospam--at)gmail.com] Sent: Thursday, December 29, 2005 4:27 AM To: seaint(--nospam--at)seaint.org Subject: Re: Column Design ) Yes it means one set of forces at each end. There are two ends of the column for which we get a total of two sets of forces. ) We can get the bending/SF/axial diagrams for each column from the forces at their ends. For example, a column of height 10 m is there. We get the bending moment diagram in both the directions (say X and Y). Let the maximum bending moment in X-dir occur at 2 m from the bottom and max. BM in Y-dir occur at 5 m from bottom. We get the axial force daigram, Let the maximum axial force be at the bottom of the column. But all these are not at the same location from the bottom, so which section of the column is critical for design. And another thing, let us suppose we have 500 columns in a structure. Then we cant do bending/shear/axial diagrams to find max bending/shear/axial for each column. The general procedure I saw is one takes maximum of the column reactions for design. But I feel one should also consider the direction of the moments at both the ends. If they are in same dir how to take their effect, and if they are in opposite direction how to consider. Santhosh On 12/29/05, Polhemus, Bill <BPolhemus(--nospam--at)wje.com> wrote: > It isn't clear to me what you mean be "not possible to get the bending/SF/axial diagrams." If you know the forces at each end of the column, and you know the lateral loading on the column if any, of COURSE you can get the diagram. Unless this is a response spectrum analysis? > > When you say "two sets of forces at each end," do you mean "one set in each of two orthogonal directions" or should this read "ONE set of forces at each (of two) ends"? > > More information is required. > > ________________________________ > > From: Santhosh Kumar Yedidi [mailto:sant527(--nospam--at)gmail.com] > > After frame analysis we get two sets of forces at each end of a > vertical member (column). But while doing design we generally require > only one set of forces. So can any one help which set of forces have > to be considered. > > ******* ****** ******* ******** ******* ******* ******* *** * Read list FAQ at: http://www.seaint.org/list_FAQ.asp * * This email was sent to you via Structural Engineers * Association of Southern California (SEAOSC) server. To * subscribe (no fee) or UnSubscribe, please go to: * * http://www.seaint.org/sealist1.asp * * Questions to seaint-ad(--nospam--at)seaint.org. 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