Civil Engineering/economy

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Question
QUESTION: Sir,
if a section is designed by both working stress method and limit state method, the section will be economical by the design of which of the 2 above methods and why?

ANSWER: Dear Arsalan

We cant say exactly because a problem of reliability has been the motivation to follow the limit state method. But from my experiences I am convinced that the limit state method is more tendency toward being economical.

Regards
BEH

---------- FOLLOW-UP ----------

QUESTION: sir,
can you give me the reason why limit state method is more economical in engineering sense?

Answer
Dear Arsalan

I didnt say that it is economical (We cant say exactly because a problem of reliability has been the motivation to follow the limit state method. But from my experiences I am convinced that the limit state method is (has)  more tendency toward being economical.)

It is dependent of the ratio of different loadings witrh respect to total loading. For example say you have LL=200 , DL = 400 The limit state give you a safety factor of   around (LL+DL)x 0.9 /( 1.6 LL +1.2 DL)= 0.61 < 1/1.5=0.67 which imply a more economical design but for different loading and different materials and different actions( shear, moment, axial force) it differs.

Regards
Beh  

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