AS3600-2018 (amdt 2) CL8.2.8.2

[Gishin1]

Hi all,

CL 8.2.8.2, under equation 8.2.8.2(1), it states that the total tension force "need not be more than that required at the section with the maximum tension force demand for flexure, axial, and torsion"

Does this mean to say, that if there is no torsion or axial force, then a cross section can be design for the tension force due to flexure only, T=M/z? And the additional tension force from shear does not need to be accommodated?

From my checks, the additional tension forces due to shear can add substantial tension reinforcement, that never would have been required from the 2009 code.

 

[cooperDBM]

It means that there is no need to add shear tension at sections where the flexural/axial/torsion tension force is at a peak. For instance midspan for positive flexure, or over a continuous support for negative flexure. In figure 8.2.8.3 this situation is shown as the flattening of curve B near the peak moment so that it isn't higher than curve A. Curve B looks to be mislabeled as it should represent equation 8.2.8.2(1), Ttd. Delta_Ftd is shown, not as curve B, in the diagram.

 

[rapt]

Gishin1,

It was also required in the 2009 code, as the simplified D offset rule for reinforcement in RC design and a requirement that the Moment be offset by D for PT design. But it did not cover a lot of cases well, including PT, changes in section etc. And the D was from the old days when the shear angle was 45 degrees.

It says that the total force at any cross-section for shear + flexure + torsion + axial is limited to the amount required for the sum of that required for flexure + torsion + axial at the point requiring the maximum amount of reinforcement from those in that moment zone.

If you think about it at the maximum negative moment point, there is no shear angle at that point so deltaFtd there is zero and you only need flexure + torsion + axial. As you move away from the maximum point, the angle increases from 0 and an increasing amount is required the further you move from the maximum point until you reach the full shear angle which is about 2dv from the support.

It does not add reinforcement, it defines the distance it has to extend.

 

[Gishin1]

Hi guys, thanks for the response. That makes sense. I can seen that figure 8.2.8 is already shown in the 2009 commentary, which explains the situation.

Thanks for clarifying