BS 5950 Elastic Design Method

[LYO]

Hi there,

"When a structure is subjected to sustained vibration and stress reversal caused by operating equipment, plastic design method shall not be used."

My understanding on this requirement is that the structure should be designed to elastic stage only where plastic forming in steel member should not allowed. From few literatures, American standard define "plastic design method" as Limit state design (LRFD) method while "elastic design method" as Allowable stress design (ASD) method.

BS 5950 is a limit state design by applying safety factor on forces for load prediction. It use ultimate steel yield strenght (or design strength) to determine member capacity (reduction in strength for thicker/slender member). Classification of member differentiate the use of either Plastic Modulus (S) or Elastic Modulus (Z) for member bending capacity, where only semi-compact sections are refering to Elastic modulus.

Appreciate if anyone can advise me on how to design the structure to elastic stage with BS 5950.
P/S : This topic is subject to BS code only but not Eurocode.

Many many thanks

 

[Retrograde]

By "plastic design method" I believe they are referring to an overall global plastic collapse mechanism analysis.

 

[BAretired]

I would interpret "plastic design method" in the same way as Retrograde. LRFD in the USA or LSD in Canada are perfectly legitimate methods of analyzing and proportioning members with vibration and stress reversal, but the determination of forces and moments is carried out using elastic analysis.

BA

 

[LYO]

thank you both
LYO