Dynamic foundations - 5x the weight of equipment 1

[LearnerN]

I recently heard that some ACI resource on dynamic foundations says that the foundation can be sized as a block of reinforced concrete 5x the weight of the dynamic equipment. If someone knows what I'm referring to, could you mention what resource and section of the resource this is located in? Thank you!

 

[dcarr82775]

ACI 351 is the document you are probably thinking of.

It is an old rule of thumb. If your foundation weighs at least 5* the weight of the machine you can essentially ignore dynamic affects on the foundation.

 

[JedClampett]

ACI 350.4R, Section 4.5.4, "...Some sources recommend a minimum foundation to mass ratios, generally in the range of 2 to 5...."
After that there's some weaselly language that this doesn't always work.

 

[bootlegend]

Here's the paragraph from ACI 351.3R-04. There are some other rules of thumb concerning size and thickness in the document as well that you may want to look into.

"A long-established rule-of-thumb for machinery on blocktype
foundations is to make the weight of the foundation
block at least three times the weight of a rotating machine
and at least five times the weight of a reciprocating machine.
For pile-supported foundations, these ratios are sometimes
reduced so that the foundation block weight, including pile
cap, is at least 2-1/2 times the weight of a rotating machine
and at least four times the weight of a reciprocating machine.
These ratios are machine weights inclusive of moving and
stationary parts as compared with the weight of the concrete
foundation block. Additionally, many designers require the
foundation to be of such weight that the resultant of lateral
and vertical loads falls within the middle third of the foundation
base. That is, the net effect of lateral and vertical loads or the
eccentricity of the vertical load should not cause uplift."

 

[Tmoose]

An older (1980s) ACI Publications was a collection of papers. Some concentrated on mass ratios.

At least one emphasized other points.
After minimum dimensions to maintain equipment alignment are established, The mass of the foundation is almost secondary.

The loading of the soil is very important.
There are some scary pictures of foundation "failures" where semi-circular slip occured.

For rotating machinery the ratio of the height of the rotating shaft to the transverse dimension sure is very important, too.

http://www.jalopyjournal.com/wp-content/uploads/2014/12/HurstCVR.jpg

 

[Guastavino]

I just sat through a asce webinar on this with Alexander Newman. It's ACI351. He brought that up as the "rules of thumb" and said it was likely good up to 5,000# equipment. Beyond that he recommended a more sophisticated analysis, and believe me, it looked sophisticated.

Ironically, in the webinar, he even hinted that he usually subs this work out when it gets large and complex...haha I was like, the guy you sub it to should help teach this then...