Machine Foundation Design

[jheidt2543]

Fellow Engineers:

Machine foundation design can be a pretty complex problem and I have many references to help me with it. I have developed a standard letter outlining the parameters I need from the Owner and the machine Manufacturer in order to design the foundation. However, I have two reoccurring problems and I am wondering what other engineers do in similar situations when asked to design a machine foundation:

1. In some situations, the only information given is a drawing from the machine manufacture with the machine’s foot print and anchor bolt layout along with a note something like “total dynamic load is 130,000 lbs.” Getting information from some machine manufacturers is like pulling teeth. They site liability and confidentiality reasons (seems lame to me). Do you have the same problem? If so, how do you proceed or do you just say no to the job?

2. Sometimes the buyer of the machine wants a turnkey price for the design and construction of the machine foundation. So, I give the contractor a price to design the foundation, but he also needs a preliminary “guesstimate” of the design for his pricing of the construction costs. Does anyone have a rough, quick “rule of thumb” to give approximate foundation size for budget pricing of construction cost? I have seen and used, from time to time, 1.5 to 2.0 times the total weight of the machine for the weight of the concrete base and then just work out a reasonable block size. This is pretty crude and can get pretty big, thus loosing the job before even getting started. What do some of you do?

Thanks in advance for your thoughts.

 

I have analyzed many dynamic foundations. The rule of thumb is 3 times the machine weight for centrifical machines and 5 times for reciprocating machines. It is not smart to violate rules of thumb. Remember the Tacoma Narrows Bridge?
You need to have the rpm and imbalance of the machine and accurate dynamic soil properties in order to do a good analysis. There are approximations for this but keep in mind that when problems develope the foundation is the first thing everyone blames. You need to do a thorough analysis job to protect yourself.
These machines are expensive, particurlarly when they fail and the foundation is cheap relative to the mechanical costs.