Skirt Openings

[michigander]

IS there a methodology to analyze reinforcement on an opening in a column skirt? Or is it reasonable to just replace the removed area with equivalent reinforcement?

Thanks in advance...

 

[Mandeep1]

Dear michigander,

In the skirt opening evaluation, you have to consider the lost and inertia. Because the stress on the skirt is,

= Force / area + Moment / inertia

on the compressive side. The moment typically from wind/seismic.

So, if you just replace the area then you did not perform the complete evaluation. I have seen some engineers treat it as a nozzle, but the area replacement calculation is only valid for pressure loading.

So, to perform this analysis properly, you have to compute the area at the weakest section and inertia at weakest section and then compute the stress in the skirt. You may have to perform this check at various sections to get the weakest one. You can check the DIN pressure vessel code they have procedure for a single opening.

PV Elite pressure vessel design software performs the skirt opening evaluation. You can specify straight or tapered skirt, one or multiple openings at various elevations, circular or elliptical or obround opening shape and with or without a frame.

Hope this helps.

 

[jte]

As I stated in thread809-115633...

One approach commonly used on for example vessel skirt access holes is simply area replacement. If the cross section (looking down) of the cutout is say 24" x 1" thk then add a collar on the hole which supplies 12 sq.in. on each side. Simplistic but logical and effective: You are looking to maintain the moment of inertia of the original section. By replacing the removed area the A*D^2 term remains the same. This, of course, is applicable when the cutout is not in such a small diameter vessel such that the centroid of the cutout is significantly larger than the centroid of the collar (reinforcement). I ran into this issue with a small diameter vessel which needed a part of its shell replaced.

jt