STRUCTURAL ENGINEERING FORUM OF INDIA [SEFI]

udayakumar · SEFI Member Joined: 22 Jan 2015 Posts: 19

Dear All,

I could successfully learn Staad from User manual and manage to do simple analysis of frames now. Thanks to Sefians for continuous support. Now I have a doubt:

When we view the output after the frame analysis we are getting the following values of forces and moments for each joint from staad pro viz:

Forces: Axial, Shear Y and Shear Z
Moments: Torsion, MOM Y and MOM Z

Please clarify that which value of Shear Force and Bending Moment should be considered for concrete design out of the above 3 values?

Best Regards
R.Udayakumar.

vijay yadav · SEFI Member Joined: 04 Aug 2014 Posts: 5

DEAR UDAY JI

FOR COLUMN DESIGN AXIAL MZ AND MY ARE TAKEN. FOR BEAM MZ AND FY ARE TAKEN FOR FLEXURE AND SHEAR RESPECTIVELY.

udayakumar · SEFI Member Joined: 22 Jan 2015 Posts: 19

Dear Vijay Ji,

Thankyou for your reply.

1. You have mentioned that we have to take both Mz and My for column design. I agree to this if it is a biaxial bending case. Suppose if it is a Uniaxial bending case, Shall i take maximum of this two values?

2. Also kindly clarify, why My and Fz are neglected in Beam design?

3. Please post it if there is any reference material to read and understand about the above practice.

Best Regards
R.Udayakumar.

Dr. N. Subramanian · Posted: Wed Jun 24, 2015 12:19 amPost subject:

Dear Er Udayakumar,
You have written

"1. You have mentioned that we have to take both Mz and My for column design. I agree to this if it is a biaxial bending case. Suppose if it is a Uniaxial bending case, Shall i take maximum of this two values?"

What do you mean by this? When both M_zand M_yare present, it is clearly biaxial bending. Only if one of them is nearly equal to zero or having minimal values you can treat it as uniaxial!

You have written
"2. Also kindly clarify, why My and Fz are neglected in Beam design?"

我不确定我和Fz在你的情况中。在3D analysis, you will get all the stress resultants. Three moments and three forces. Torsional moments may be neglected if there are due to compatibility torsion. However they may not be neglected in edge beams. Axial force may be neglected if it is less than 10% of the axial capacity.

Best wishes,
NS

es_jayakumar · Posted: Wed Jun 24, 2015 4:09 amPost subject:

Sir,
Myis the moment about the vertical axis (in STAAD, Y is the vertical direction and My tries to twist this axis). Hence, Mr. Udaykumar is perhaps referring to the bending of the beams in the horizontal plane (X-Z). Though this may be negligible in normal cases, it can be considerable when torsion come into play for the building about the vertical axis, when centre of gravity and centre of rigidity do not coincide and seismic / wind forces are predominant . He may be asking why this (horizontal) bending need not be considered in the design of such beams.

Regards,
E S Jayakumar

udayakumar · SEFI Member Joined: 22 Jan 2015 Posts: 19

Dear Sir, (Dr.Subramanian and Er.Jayakumar)

Thank you for the clarification.

It has improved my understanding on the interpretation of results from 3D analysis. I will analyze once again and get back to you if required.

Best Regards
R.Udayakumar.