calculation of K, slenderness ratio 1

[hichar]

Hello
I want to ask you, did sap2000 make the calculation of K by himself??
Or i must to set K manualy for evry frame( by design, overwrite, k major and k minor)

Thank you

 

[hichar]

By exemple
If i have a column wich is fixed end in one side and free from the athor side
Did sap2000 will calculate K for this columna as K=2 or i must put it by steel design-overwrite

Thank you

 

[johnbridge231]

SAP2000 will calculate the K by its own, after classifying the column to sway or not sway.
In this calculation, it will account for the stiffness offered from the beamas runningt into the sdge nodes of the examined column.
So you will just need to check the validity of the results and in same (few) cases modify them.

Regards.

Analysis and Design of arbitrary cross sections
Reinforcement design to all major codes
Moment Curvature analysis

http://www.engissol.com/cross-section-analysis-design.html

 

[hichar]

Dear johnbridge
Up to your experience, wich are the few case that i must modify K

Another question about sway or not sway, do you mean if i realesed the frame(not sway), not released(sway)

Thank you

 

[johnbridge231]

Dear hichar,

Frame are classified to sway and not sway as per the relevant design code used. For instance Eurocode assumes moment frames almost always as sway, whereas braced frames are assumed non-sway.

As for the K factor, you should always check it, especially in sloped elements, or frames that have one or more intermediate joints.


Analysis and Design of arbitrary cross sections
Reinforcement design to all major codes
Moment Curvature analysis

http://www.engissol.com/cross-section-analysis-design.html

 

[hichar]

Dear johnbridge
I done a momemt frame design, 4 beams and 4 columns, sap2000 had calculate the effective length factor, but the results numbers was strange!

for columns:
Kmajor= 2.2
Kminor=2

 

[johnbridge231]

Dear hichar,

this is so because probably SAP2000 did classify the frames as sway. If you add braces, you will notice that the K factor will be less than 1.0 in that direction. (The frame will then be classified as non sway frame in that direction)

Regards.

Analysis and Design of arbitrary cross sections
Reinforcement design to all major codes
Moment Curvature analysis

http://www.engissol.com/cross-section-analysis-design.html

 

[hichar]

I did a design to a columns and i made it fixed end from up and down
Result:
K=1.3
It must be 0.5!!

 

[johnbridge231]

It should be 0.5 only if the frame is braced in that direction, or if a restraint (for example vertical roller) is assigned to the top node of the column.


Analysis and Design of arbitrary cross sections
Reinforcement design to all major codes
Moment Curvature analysis

http://www.engissol.com/cross-section-analysis-design.html

 

[hichar]

Dear john
that what i did, the columns is fixed end from down and u2,u3,r1,r2,r3 restrained and u1 free, the result doesent 0.5
plz try it
and try a columns fixed end from down and free frm up, it must K=2 (Le=2L) but result in sap diferent !!