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# Designer’s Conflict of Safety vs. Economy - PowerPoint PPT Presentation

Designer’s Conflict of Safety vs. Economy. a Serious Task for Codes’ Elaborators. The design must accomplish strict prescriptions of safety and serviceability. Thereby designer is forced to use enough material of good quality and design legalized long time proved systems.

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### Designer’s Conflict of Safety vs. Economy

a Serious Task for Codes’ Elaborators

The design must accomplish strict prescriptions of safety and serviceability. Thereby designer is forced to use enough material of good quality and design legalized long time proved systems.

The price of designed object must accomplish demands of contemporary eco-nomy, i.e. designer is forced to select the material of appropriate price (may be not expensive) and seek for new unproved systems giving the hope of lowest cost.

All the time designers are facing two principal antagonistic demands:

The probabilistic constitutive requirement of safety is given by this relation:

Pf = P[(RV - S) < 0] < Pd

Pf - probability of failure

Pd - target probability

To solve the designer’s conflict target probabilities have to be set in the previous equation, however, the target probabilities must be two:

• Ultimate limit states target probability Pd

• Serviceability limit states target probability Pd

Notice: The value of target probability impact on cost of project

Ultimate limit states target probability10-7 < Pd< 10-3

Serviceability limit states target probability 10-2 < Pd< 10-1

Notice: The probability of crash of an airplane in an interval of one- hour flight is assumed as 10-7.

Another approach comes up from one-year probability of damage Pd1 and appoints the target probability for n-years interval

However, this relation does not respect any changeability of intensity of defects (so called bathtub curve)

C0 denotes the price of procure of the object

Cf denotes expenses coherent with transgression of the limit state

The more is Cf- the less is Pd.

Have a nice time