AS1170.4 Draft 2

[Trenno]

New AS1170.4 draft is out for public comment, closing 18/01/24.

Seems like reo rates may be on the rise again with the introduction of these two proposed admendments.

 

[human909]

To me it just seems engineers should be able to determine the mandated buiding base shears from something more than an equation introduced 15 years ago and with the only variables being height and lateral system.

Exactly. Surely we should be considering stiffness and mass to find the natural period?

I have no complaints against an simple formula that limits engineers from making unconservative choices but surely we should have enough faith in engineers to be able to do a basic stiffness and mass calculation? I'll be the first to admit that my seismic knowledge is far from immense surely we can do better.

 

[li0ngalahad]

Glad some sort of base shear scaling was reintroduced, however it seems to me that the 50m cut off does not make much sense, should be something gradual, not full 70% scaling at 49.9m and no scaling at all at 50.1m. This will lead to some engineers to propose developers that have structures close to 50 m tall to slightly increase the height in order to massively reduce the seismic loads

 

[Just Some Nerd]

This will lead to some engineers to propose developers that have structures close to 50 m tall to slightly increase the height in order to massively reduce the seismic loads

On one hand, I agree with you, on the other hand, would be really good to get some additional headroom for transfer slab depths...

----------------------------------------------------------------------

Why yes, I do in fact have no idea what I'm talking about

 

[bugbus]

Why do so many of the Australian standards insist on these hard cut-off points where one rule suddenly stops applying and another one kicks in, just because something is now 1mm longer than it was before?

 

[rapt]

Bugbus

It is not just Australian codes. All do it. I have been trying to remove as many as possible in the codes I am involved in.

I have passed this comment on to the 1170.4 committee in case no one else has in response to the draft comment requests. Hopefully it is not too late.

 

[IDS]

The public draft is open for comment until 25th January next year.

Doug Jenkins
Interactive Design Services

http://newtonexcelbach.wordpress.com/

 

[li0ngalahad]

I just received confirmation, following a comment I have left on the draft, that buildings taller than 50m will now require 50% base shear scaling. Still a big jump from 70% to 50% at 50m but that's a great improvement from the previous 70%-0%.

 

[Just Some Nerd]

Still irks me that they didn't opt for a smooth transition, to be honest.

----------------------------------------------------------------------

Why yes, I do in fact have no idea what I'm talking about

 

[Trenno]

Be interesting to read the commentary (in ~5yrs time) to see how these scaling factors were derived.

 

[Just Some Nerd]

It irks me to no end that a group of people can write a code and ostensibly have a rationale for every decision made in it, but take 5 years to actually communicate that rationale to the people wanting to use the code. Aussies are inexperienced enough with seismic as it is, the less guesswork the better.

----------------------------------------------------------------------

Why yes, I do in fact have no idea what I'm talking about

 

[SRL V1.0]

Is anyone able to send a copy of the draft through?
The download location is inaccessible now with the comment period finishing up.

 

[li0ngalahad]

Still irks me that they didn't opt for a smooth transition, to be honest.

Yeah I did propose a smooth transition through a simple linear equation in my comment however it looks like the committee prefers to adopt a more simplistic approach.

 

[Trenno]

FYI

Webinar Link

 

[sdz]

AS 1170.4-2007 Commentary 2nd Edition (2021)

https://aees.org.au/product-category/commentary/

Ooo eee ooo ah ah ting tang walla walla bing bang
Ooo eee ooo ah ah ting tang walla walla bing bang

 

[human909]

I'm glad to see that I'm not crazy and that the seismic hazard maps ARE contour maps. I still see engineers and online resources failing to interpret a contour map properly.

My issue (a little pedantic) is their approach in this update to remove the confusion actually adds to the confusion. By marking 0.08 low points on the contour map in inconsistence places it gives false and misleading information. If 0.08 is the minimum they need the 0.08 contour on the map!

EDIT: I suppose I should spend less time complaining here and more time commenting on the draft standard.

 

[Just Some Nerd]

I actually think that a shaded area would make it very clear where it is 0.8 so people don't waste time trying to read different contour lines. If the site is in the green area, it's 0.08, if it's elsewhere, then it should be fairly easy to tell because the contours will actually be there. H

----------------------------------------------------------------------

Why yes, I do in fact have no idea what I'm talking about

 

[Retrograde]

Unfortunately they did not mention the new 80% limit on dynamic analysis in the Concrete Institute webinar.

 

[human909]

I actually think that a shaded area would make it very clear where it is 0.8 so people don't waste time trying to read different contour lines. If the site is in the green area, it's 0.08, if it's elsewhere, then it should be fairly easy to tell because the contours will actually be there. H

Oh I agree! I don't know why they didn't include a shaded area in the actual standard.

 

[li0ngalahad]

Unfortunately they did not mention the new 80% limit on dynamic analysis in the Concrete Institute webinar.

Assume you meant 70%.

I thought about asking a question, however I think it's quite clear now they will introduce 50% scaling for building higher than 50m and 70% for lower than 50m, not much needing clarification there. Don't necessarily agree with the sudden change happening at 50m however I am happy some scaling will be required no matter what, and happy enough this will be clear and the same for everyone. Currently with no scaling required I saw some engineers applying no scalign at all even when going aggressive on stiffness reduction factors on their structure, which is pretty crazy - while I've been accused of being too conservative because I was applying scaling factors to my spectrum case. Glad this will be no more.

 

[li0ngalahad]

Got a notification from SAI Global that AS1170.4 2007 has become superseded however I see no new standard been released yet.
Does anyone know if we will be having the new earthquake load standard today, or in the next coming days?