Environmental Loading for Productized Engineered Stuff (Integrated Process Equipment etc)

[TLHS]

Hey all,

We've had some similar conversations before, but I'm taking a look at some standard process skids and similar items and want to see other people's opinions. What would you do for standardized loadings? As a starting point let's assume we're talking about the US.

My instinct is that trying to envelope absolute worst case environmental criteria is a terrible plan. You'll end up triggering all sorts of hard to deal with requirements and get problems like the snow load and seismic load interacting to make ridiculous seismic forces. You also start having overturning and load reversal even on fairly squat items.

My thought is that end purchasers from really high wind zones and really high seismic zones are used to having additional scrutiny, so excluding them from a standard qualification and doing specific investigations for those purchasers isn't a big deal and is probably a good standard of care regardless. It's not worth trying to design for all the edge case issues as a starting point. All of the items I'm considering are ground mounted, so they don't have to deal with the huge amplifications for seismic inside buildings, or anything of that sort.

So my thoughts are:

Wind Speed: 130 or 140mph, Exposure C

Seismic: Ss=1, Site Class D

I have to look at snow a bit still, but is likely not going to control much in design.

Does this seem like a reasonable strategy? I can't find much in the way of industry practice on this stuff, unfortunately.

 

[phamENG]

It sounds reasonable enough, though you may want to reconsider what your 'edge cases' are for wind. I'd suggest using 115 or 120 as your top end. The contours on the wind map get quite small once you get over 120, so you're not gaining much ground while increasing structural requirements for everyone else. Unless there's a high concentration of buyers in coastal Carolina, Georgia, and within a hundred miles or so of the northern gulf coast, 130 is too high.

 

[milkshakelake]

When I worked for a company that did standardized designs across US for specific customers, we had 3 different tiers for each standard design for modular frames. I can't remember the limits off the top of my head and don't have access to those anymore. It was something like Ss=0.5, Ss=1, Ss=1.5, but don't take my word for it; just giving the basic idea. Similar thing for wind speeds, with both limits on one drawing. It covered every case. They also got ICC-ES certification on one of the high tier designs, which had some pretty outrageous sizes and connections. But then again, that company was big and had access to a lot of resources, so they had the staff to make that happen and they somehow also charged very low fees for these standardized designs (one of my duties was chasing down clients for unpaid bills). They got some money by signing and sealing the drawing for various states. I don't know your situation, but it might be overkill for a smaller firm. I wouldn't be able to make that work financially with 3 tiers of design.

The high tier one was needed for Florida at some point, and we needed to submit a letter to their building department specifically stating that it complies with Florida wind speed in that location.

They also had standardized foundation designs for industrial tanks, but I can't quite remember the tiering on those. If I recall correctly, those can't be used right out of the box; they generally need to be used in conjunction with a soil report. But it's been a while and my memory is fuzzy.

Just take everything here with a grain of salt. That company was very much mismanaged, so even if they were doing it, it doesn't mean it's right. I tend to agree with you that higher environmental loading requires special care. But it can and has been done.

 

[HTURKAK]

Will you please be more specific for the type of process eq, non building str , stationary eq ?

Just to give some indication,

- API 650 suggests ''The design wind pressure on shell (PWS) shall be 0.86 kPa (V/190)2 '' which corresponds 140 kph wind speed
- I remember 0.2G minimum earthquake loading for steel stacks

The design criteria should comply with the minimum requirements of the relevant standard if there is ..








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