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Re: Boggled Out By Load Combinations

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Bill Allen wrote:

Bill –

 

Believe it or not, I think I can accommodate the force (think: rubber band – AE is very small). Allowing for the movement (sliding connection) in my case would create more problems than it solves.

 

Sooo…If I understand your response to the original point, you’re saying to take Delta_sub_s and divide by 1.4 to arrive at the ASD level displacement for design of this rubber band?

 

Thanks,

 

T. William (Bill) Allen, S.E. (CA #2607)



Bill,
As far I understood, you would like to install a "fuse" which should remain intact during service life but could fail and require repairs after a 475 year earthquake. If so, flexural "fuse" would be easier to design than axial. If your tie has to undergo Delta_sub_M elastically, then the force would be so large that it does not serve the purpose becasue it would affect your load distribution.

If you are absolutely interested in an axial member, you should be checking at what force level the element reaches the yield strain; after that the element will theoretically experience a constant force (= yeild stress*Area) untill it reaches the ultimate strain . But in reality the maximum force will be ultimate stress (Fu)*Area. Similar reasoning should apply if your member is flexural, i.e. the question will be when a plastic hinge forms.

There does not appear a need to include any factors; it all depends on your design - how flexible you want the tie to be.

Suresh Acharya, S.E.