Design factor, Uncertainties, Maximum allowable load, Load causing failure

DF = Fl/Lmax


DF = UFl/ULmax


UFl = 1/(1 - Uf/100)


ULmax = 1/(1 + Ux/100)


where:

DF = design factor

Fl = failure load, load causing a failure, load which causes a loss of function of the part

Lmax = maximum allowable load

UFl = uncertainty factor for load causing failure. UFl must increase when uf is present

ULmax = uncertainty factor for maximum load. ULmax must decrease when ux is present

Uf = % uncertainty of a load that causes a failure

Ux = % uncertainty of the maximum load


1. Problem: Design factor & Maximum allowable load

find:

DF = design factor

Lmax = maximum allowable load that will account for or offset uncertainties


given:

Uf = 10%

Ux = 25%

Fl = 3000 lbs


solution:

DF = UFl/ULmax


UFl = 1/(1 - Uf/100)

UFl = 1/(1 - 10/100)

UFl = 1/(1 - 0.10)

UFl = 1/(0.90)

UFl = 1.11


ULmax = 1/(1 + Ux/100)

ULmax = 1/(1 + 25/100)

ULmax = 1/(1 + 0.25)

ULmax = 1/(1.25)

ULmax = 0.8


DF = UFl/ULmax

DF = 1.11/0.8

DF = 1.4


Lmax = Fl/DF

Lmax = 3000/1.4

Lmax = 2143 lbs