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Staad Design - Tension Column - erroneous?
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mtamil
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PostPosted: Sun Apr 13, 2014 2:28 pm    Post subject: Reply with quote

sakumar79 wrote:
Dear Sir,
    Without code recommendation, it is difficult to justify the same. How is the factor arrived? I generally prefer to design 1.5 (DL+EL) with full EL only... If there is any legal issue at some point, the reviewers may not accept such reduction.

Yours sincerely
Arunkumar


Dear Er. Arunkumar,

Apologies for this delayed reply.

This particular load combination is to consider the "Minimum Dead Weight Condition" during construction or the unoccupied condition.

And, I am not able to imagine a Live Load having only Mass contributing to Seismic Force but with zero weight (gravity).

On the contrary there can be live load with (100% weight) reduced response to earth vibrations. Which explains the reduced LL mass considerations in seismic load computations. (Though experts can have their own view on the quantum of reduction)

Moreover, I did not come across in the codes which explicitly states to include 100% LL mass while computing Seismic forces when only DL alone is considered as gravity load.

We have got this load combiantion DL+SL (without live load mass in Seismic computations) approved by few of the Engineering offices of Public Sector companies and by Private consultants.

Regards
Tamilarasan
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mtamil
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Joined: 07 Apr 2011
Posts: 187

PostPosted: Sun Apr 13, 2014 2:52 pm    Post subject: Reply with quote

sanju_re wrote:
Reading your post, it is clear that there has been a confusion with the member end force results obtained from a load combination where Response Spectrum load case is a part of it. The major problem lies in the fact that the results of Response Spectrum ...
...
...
...
...load combination 213 produces compressionin the column. The column is designed for another load combination where thecolumn is subjected to tension. It is to be noted that the axial tension (-372.28 Kn) for which the column isdesigned using the sign of dominant mode is quite lower tensile force than theprevious case and the design forces are quite reasonable.

Regards,

SANJIB DAS


Hi Er. Sanjib Das

Welcome to the Sefi community and thanks for your very informative post. The information is new to me and I will look into it for implementation.

The focus here is on the inbuilt design module, wherein Staad considers an unrealistic tensile force in the design as against a very small tension reported in the Member end forces Table. I request you to look at my original post and review by Er. Arunkumar. I beleive you will also accept the fact that the Column design calculation (load considered for design)  by Staad is erroneous.

Please post your observations on this.

Regards
Tamilarasan.
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