MOMENT FRAME IN STEEL PIPE RACK

[ChrisBallas]

Hello Gents,

Imagine an 25m tall by 5.50m wide, two column piperack supporting 6 piping levels. The consequent frames are spaced every 9.00m.

The frame is a PINNED-BASE MOMENT FRAME
The first level is @+8.00m & carries minor piping.
The second level is @ +11m, & carries very heavy piping. From that level & onwards all other piping tiers are at 3m vertical spacing.

My HE550B columns form a sway frame; sidesway is uninhibited. Their first tie beam is @ +8.00m as mentioned above.

The second level beam (@11m) due to the heavy verTical PIPING loads needs to be an HE500B section.

The first level beam (@8m) could in respect of its structural checks be an HE360B; however I feel very unsafe (intuitively) to specify for such a tall moment frame its lowest beam (HE360B) to be weaker than the second storey (HE500B).

The intuition comes from the fact I would not like the frame stiffness dropping as we go lower & of course the K-factor for the columns would be higher but still not critical.

Can I specify for a moment frame the lowest beam (which is @ 8m) being weaker than the second storey one (@11m). Does it make sense?

Regards,
Chris

 

[paddingtongreen]

I see no intrinsic problem but you might find that the lateral load case drives the member selection. The bottom section of column is longer than the one above and it is pinned/fixed where the shorter section above is fixed/fixed, how much of that moment will go into the lowest beam depends on the stiffness ratios which appear to favor the columns. If you get into a problem with drift, then all members will likely be selected on stiffness not strength.

Michael.
"Science adjusts its views based on what's observed. Faith is the denial of observation so that belief can be preserved." ~ Tim Minchin

 

[johnbridge231]

I also do not see any problem.

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