Yeah, tends to err on the side of conservative multiplicative factors which lowers theoretical to practical results. Good approximations though if you need something in a hurry and want to have safety factors near two.
Kenneth J Hueston, PEng
Principal
Sturni-Hueston Engineering Inc
Edmonton, Alberta Canada
Do you have an application or reasoning behind your enquiry? I say this only because every equation has multiple principles and can be used in several different cases. If you can narrow things down a bit, someone might be able to point you in the right direction and be able to find you information SPECIFICALLY regarding what you are working on.
