Moment Capacity variation between STAAD result and Manual Calculation

Hello All,

I was manually calculating the bending capacity of the built up I sections as per IS-800 and found that the results for compact and semi-compact webs were not matching with the STAAD results.

I have attached the snap of my manual calculation, as well as the STAAD result. The sectional properties are matching exactly.

Kindly provide your expertise in this regard. It will be very much helpful.

Also, if we see the section classification for the attached member [450x5(web) + 175x8(flanges)], the web is classified as "Compact" in STAAD, whereas actual classification has to be "Semi-Compact". Clarify this as well.

Regards,

Parishith J

PDFPDF8875.Frame.std

  • If you provide the design capacity check for the section it would be very much helpful.

    For the section classification of the web, I used the category under "Neutral Axis at Mid depth", which would yield 450/5 = 90.

    Which is greater than 89.25 [105 X 0.85 (105E)]. So, the web is falling between 105E and 126E, hence "Semi-Compact".

    This was my consideration.

    Based on the STAAD result, the web classification is reported as "Compact". So, my query is whether we should not use "Neutral Axis at mid depth" criteria to find the classification for the web?

    And in my case, I am getting a "Semi-Compact" web, whereas the result produced by STAAD is "Compact". - So following the code, we are getting two different classification for a single case. The safe option is to go with the conservative one, right. In that case, why STAAD is not adopting "Semi-Compact"..?