AS3600-2018 Amendment 2 - possible error

[NTCONLINE]

Hi everyone,

You are probably aware that AS3600 amendment 2 was released end of May (1 month ago) with a significant change in the Shear section.

1. Could anyone please let me know if the V* used in the shear clauses 8.2.1.6 and 8.2.3.1 is now just pure shear (i.e. not the equivalent shear V*eq as in the previous Amendment 1)?

When I checked the Symbol Definition section, interestingly, V* and V*eq are both there.
Specifically, "V*eq = the equivalent factored shear (see Clause 8.2.1.2)" but I checked 8.2.1.2 there is no V*eq as mentioned.

2. In clause 8.2.7, in the new code, I believe it is a mistake in equation 8.2.7(2)
the term " + phiVuc" in that equation should be " - phiVus". Am I wrong here?

3. The definition of "Ao" and "uo" on page 121 (new code) are exactly the same, but I believe this is another mistake.

AS3600-new code with Amendment 2

https://files.engineering.com/getfi...9c3-4a99-936d-b067b6b7e672&file=AS3600-A2.pdf

Thank you
NTC

 

[rapt]

V*eq has been removed. Should have gone from the definitions as well. Torsion and shear are being separated again.

The new 8.2.7(2) is correct. The original formula with Vus was being misused, as Vus should have been limited to V* - phi Vuc in that equation. Designers were putting in lots of vertical reinforcement resulting in a high value of Vus and thus requiring no longitudinal reinforcement for shear, which was clearly wrong.

Checking on u0, but I assume it should be "perimeter of the " area enclosed by

 

[NTCONLINE]

Thanks, Rapt,
But could you please confirm again that in the equation 8.2.7(2)
it is +phiVuc instead of -phiVuc?


Also, what is the implication for the RC column design?
Would the users of the standard have to exclude the longitudinal area for shear/torsion, and then, the remaining longitudinal area is accounted for Bending-Axial interaction diagram?

Thanks
NTC

 

[rapt]

As I said,

"The new 8.2.7(2) is correct."

It is a very simple substitution into the previous formula to get the current one. I gave you the solution in my last post. Vus = V* - phi Vuc.

V* - .5Vus

Vus = V* - phi Vuc

After substitution for Vus it becomes a + for the Vuc term!

I do not understand your problem for column design.

 

[NTCONLINE]

Thanks again Gill,

With your explanation about the substitution Vus = V* - phi Vuc, then it makes sense, mathematically, with the new eq 8.2.7(2)

Without your explanation, as in the case that lots of engineers won't know, I believe it doesn't make any sense to take the sum of design action and the capacity.

The original equation was much better, provided the amendment provides fixes as you stated Vus is capped at V*-Vuc.

My second question regarding the column design is as follows:
Let assume the total longitudinal steel area in the column section is A = A1 + A2.
Where A1 is the longitudinal steel area to carry the required additional longitudinal tension forces caused by shear and torsion of the column by clause 8.2.7.

Now I want to plot the interaction diagram (axial load - moment diagram) like in Figure 10.6.2.1.
To determine those points (Squash load, decompression, balanced, pure bending etc..) should I use the total steel in the section, or should I just allow to use A2
(which is = A - A1
= Total longitudinal area less the longitudinal area amount required for shear/torsion)

I hope my question makes sense and thank you for your input.

Regards
NTC

 

[rapt]

It is much safer to include the "cap" in the equation. Otherwise some wordsmith will think of a way to get around the wording. The only cap now is that
phi Vuc <= V*, or
.5 (V* + phi Vuc) < = V*

So if you have excess phi Vc, you cannot use it!

For the column, total reinforcement.

 

[Settingsun]

How does it happen that V*eq is incorporated then written out so soon? Change of author for the section with a different opinion, or not thought through in the first place? These changes cost time for designers which would be better spent in other ways.