AS3600. prestressed column buckling load

[geopat69]

hi
In regard to. cl 10.4.4 of AS3600 and prestressed columns, can anyone provide advice on whether or not the calculation of the real buckling load Nc should have the prestressing force deducted from its value.

Afterall, doesn't the prestressing contribute to buckling? thus:'real' Nc = Nc from code minus compression from Prestress.?

 

[Ingenuity]

No...and no.

The prestressing force has no effect on the column buckling. The prestressed column buckles only due to it externally applied axial load.

If the prestressing was via post-tensioning in a very, very large internal duct (and not grouted) such that there was no contact between the tendon to the concrete then the prestress may be cause buckling-type effects until such a displacement that the tendon contact the duct/concrete.

The theoretical aspects of this has been covered by TY Lin and Zdenek Bazant.

 

[geopat69]

can anyone make a recommendation on whether clause 10.4.4 is applicable for a prestressed column with only prestress strands in it?

I have a feeling that 10.4.4 is specifically for columns with reinforcement and therefore is not handling prestressed case.

is there an alternative formula to calculating Nc for prestressed columns with only prestressed strands?

much appreciated.

 

[Settingsun]

The commentary for 10.4.4 (2009 code, which is essentially the same in this respect) refers specifically to prestressing.

 

[geopat69]

thanks.

But what about the alternative version of the sway moment magnifier in as3600.. essentially it adopts 0.8 on the column stiffness and is significantly easier to use for design (to get delta s) However... there is no mention on it being valid for slender prestressed columns.