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Minimum design actions to AS4100

Minimum design actions to AS4100

(OP)
9.1.4 Minimum design actions on connections
Connections carrying design action effects, except for lacing connections and connections to sag rods, purlins and girts, shall be designed to transmit the greater of—
(a) the design action in the member; and
(b) the minimum design action effects expressed either as the value or the factor times the member design capacity required by the strength limit state, specified as follows:

I've read the commentary and I'm still confused.

e.g. the commentary says "For columns that may be subject to large compressive forces and only minor tensile forces, any splice has to be designed both for the specified value for the minimum member size required to resist the compression, and for the specified value for the minimum member size required to resist the tension."

Since you can base the minimum design action on multiple minimum theoretical member size when would these rules ever apply?

For a brace member (which is what I'm looking at now) if you are required to design for 0.3 x capacity of minimum tension and compression members individually then since those minimum (theoretical) members will be working at 100% of the design load the "Minimum design actions on connections" will always be less than the calculated loads.

Have I missed something here?

RE: Minimum design actions to AS4100

sdz - if you read the preface for the 2012 commentary you will see it mentions to delete the wording "for the minimum size of member" of clause 9.1.4.

It was changed to reflect the intentions of the original panel I believe (I found a publication stating this but cant for the life of me remember where). It made little sense to me in its original form to design for 30% of the member capacity for a member being utilised at 100%!

In its current form, I treat this clause as a robustness requirement only. Sometimes we provide members heavier than required to make allowances for corrosion, impact, local effects etc and therefore it is foreseeable that minimum design actions may govern. In saying that, I would expect minimum design actions to govern connections such as splices in beams etc. much more frequently than splices in tension members since tension members are generally uniformly loaded and as such the position of the splice will not significantly impact the design loads as you would expect to be the case for a continuous floor beam or something along these lines.

Its a good question - one which I have taken up with senior engineers in the past (before the wording was changed) that usually generated a good office discussion.

Jake

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