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pAssenger (Structural) (OP)
20 Apr 10 10:52
In design manual for AISC360-05/IBC2006, it is written that;

"For the purpose of calculating K-factors , the objects are identified as columns, beam and braces. All frame objects parallel to the Z -axis are classified as columns. All objects parallel to the X -Y plane are classified as beams. The remainders are considered to be braces."

This causes, for example any inclined roof girders to be classified as braces. Is there any way to overwrite the design type property of a frame member? I couldn't see any option in the overwrite list for that.
IJR (Structural)
26 Apr 10 10:57
I think SAP2000 wont calculate K factor if there is an inclined member. If it does, is is prone to be wrong

this is stated clearly in their manuals(not sure of latest development).

The design type option in the design overwrite section has nothing to do with the K factor. It is probably something to do with seismic design.

I usually calculate K manually and input it. Wont take you much time if you have an excel window multitasking with Sap2000.

respects
ijr
stressed (Civil/Environmental)
1 May 10 13:21
SAP2000 will calculate a K factor which considers releases and stiffness of section, but in some cases you have to override this program calculated value. Use Design menu to overwrite K factors and other design parameters
pAssenger (Structural) (OP)
7 May 10 14:40
IJR, thank you for your response.
Sap2000 does calculate K factor for any member regardless of its position in space. However, as you mentioned, last thing people should do is to rely on them. (which is also indicated software's own design manual.)

Sap2000 includes several checks for each design type which AISC 360 and AISC 341 requires the designers to do. The major reason underlying why Sap2000 assigns a "design type" to each member is to handle those individual checks for each type, not to calculate so-called "true" K values.

Why I need to override "design type" parameter is just for reporting purposes. I don't want to see a warning message that tells me bracing length is not enough (Lb<=0.086ry*E/Fy) for a roof bracing member just beacause it is paralel to XY plane and so it is identified as beam. What I'm trying to tell is, warning tells me to brace my bracing members in more frequent intervals which is totally irrational since it's already a bracing member itself.

Besides that, I dont want to see any "Design Type: Brace" on  a report sheet of 18meter long IPE1000 girder and I'm bored of editing them.

Thank you for your kind responses again.
stressed (Civil/Environmental)
9 May 10 12:31
pAssenger, since SAP2000 does not automatically detect whether or not you modeled your roof or deck using area elements, you will need to select your beams and then use the main menu Design menu>Steel frame design>View/revise overwrites and assign an unbraced length to beams of something like .1 instead of default 1 to account for roof or deck bracing the beams
stressed (Civil/Environmental)
9 May 10 12:35
In my previous reply, I forgot to mention that you'll likely have to modify the unbraced length in the minor (weak) direction. One annoying limitation with eng-tips forum is that it does not let you edit posts that I can find
pAssenger (Structural) (OP)
11 May 10 10:24
stressed, thank you for your attention but as I mentioned before I have nothing to do with the unbraced length factors. Try to go through my previous post again.
stressed (Civil/Environmental)
22 May 10 11:45
I don't see where SAP2000 allows the user to change whether the section is designed as a column, beam or brace. However, you can select members to assign using Design menu overwrites to modify K factors, unbraced length ratios, Cb, etc. of your selected beam/frame members

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