AS3600 Amendment 2 Torsion Rules

[Settingsun]

What was the reason for removing the equivalent shear method for torsion design in Amendment 2? Was it unconservative? I know there are 1 or 2 people on this site who might know the view from behind the scenes.

 

[IDS]

I wasn't involved in the discussion, but I suspect it was because it wasn't clear how the equivalent shear should be applied, since the code has rules for when torsion should be included, and how the required torsion steel should be calculated, with no provision for applying an effective shear force instead.:

"8.2.5.6 Torsional resistance
The value of Tus shall be determined from the following equation: ..."
my emphasis.

Presumably there will be some discussion of this in the commentary when it is published.




Doug Jenkins
Interactive Design Services

http://newtonexcelbach.wordpress.com/

 

[Settingsun]

I thought that V*eq was treated as the design shear load but requiring closed stirrups, and took Tus as only applying in the minimum reinforcement check; Tus not being checked against any design loading. So no specific torsion design after converting to V*eq.

 

[IDS]

Steve - but Cl 8.2.5.4 in Rev. 1 says:
The amount of transverse reinforcement required for torsion shall be such that T* <= Phi.Tus

That clause has been deleted, but the same equation (but reversed) is now Equation 8.2.3.1(2) in Cl. 8.2.3.1 Design strength of a beam in shear and torsion.

So the previous version had inconsistent requirements in providing a "V*eq", but also requiring that T* <= Phi.Tus. It also had numerous inconsistencies with AS 5100.5, including in the calculation of additional longitudinal forces where V*eq is combined with T* (equation 8.2.7.1(1) in AS 3600 Rev 1.

I'm actually in the process of working through the shear and torsion provisions in the last two versions of AS 3600 and the latest AS 5100.5 to try and make sure my software complies with the latest versions, and to pick up any remaining inconsistencies.

Doug Jenkins
Interactive Design Services

http://newtonexcelbach.wordpress.com/

 

[rapt]

Steveh,

It had not been well thought out in the first place.

Worked well for me for maximum combined shear and torsion.

I liked the concept but it was inconsistent for box sections versus solid sections and was inconsistent with the logic of adding shear and torsion reinforcement which were/are treated separately. So it was being treated as a combined effect or separate effects in different clauses.

So he who was in control of shear in the code decided to remove it.

 

[Settingsun]

The amount of transverse reinforcement required for torsion shall be such that T* <= Phi.Tus

Whoops, missed that. I'm confident that the end result of what I did is OK though as I made all stirrups closed and shear dominated. I guess then it was similar in concept to AS1480:

Rapt, was it the same person who included it then removed it? What's the process for significant changes, eg are there internal briefing papers setting out the theory, use overseas, and departures necessary for simplified/practical implementation in a design code?