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Creep Shrinkage in Draft AS3600

Creep Shrinkage in Draft AS3600

(OP)
The creep shrinkage properties in the new draft of AS3600 have everything happening much faster. For example Figure 6.1.8.2(A) creep 50% complete in 200 days for a 200 thickness where Figure 3.1.7.2 in the draft has 50% complete in 60 days. Does anyone know of data to support this.

It makes a big difference to the effectiveness of pour strips.

RE: Creep Shrinkage in Draft AS3600

I haven't had the chance to look deeply into the differences between AS3600:2001 and DR05252, but I have been told that the new AS3600 will be out shortly and the Concrete Institue is organising full-day seminars on the changes between the old and new codes. I am also hesitant to start programming my spreadsheets to the draft code in-case there are any amendments before the final issue.

To be more specific to your question, I believe (not 100% sure) that the creep model in AS3600:2001 was based on some papers that were put out by Prof Gilbert from UNSW. The factor which was a function of time that gave the creep curve it's S-shape was:

k=t^0.7/(t^0.7+0.15*th)...AS3600:2001

where t is time (in days) and th is the hypothetical thickness of the cross-section.

The draft model follows:

k=t^0.8/(t^0.8+0.15*th)...DR05252

I just quickly put those equations in excel and found that old model took 113 days to achieve 50% of the long-term creep (30 years) while the draft model took 67 days to achieve 50% of the long-term creep. So things are happening faster with the draft model, I don't know what this draft model is based on but I can ask around (may not happen until these Concrete Institute Seminars kick off).

Also, I would wait for the new code to issued before using this model and I believe the BCA does give a 2 year clearance before AS3600:2009 is "Deemed-to-have-satisfied".

Good pick up, I will be mindful of this when the new code comes out.

 

RE: Creep Shrinkage in Draft AS3600

degenn,

It was developed by Gilbert. I am seeing him later this week so I will ask (he is not answering his phone as he is probably out trying to get the CIA congreess organised).

But it is not creep that controls the pour strips timing, it is shrinkage.

The reason all of this had to change was because the old code could not be applied to higher strength concretes, especially for shrinkage. I have not checked the new equations against the old for lower strength concretes.

RE: Creep Shrinkage in Draft AS3600

has the hall marks of Gilbert all over it. Try searching for R.I. Gilbert and Creep.

Arguing with an engineer is like wrestling with a pig in mud. After a while you realize that them like it

RE: Creep Shrinkage in Draft AS3600

(OP)
The original post should have said creep and shrinkage.

The k1 equation (shrinkage) and k2 equation (creep) both use the same time scale.

The ACI document ACI 209.2R-08 give info on a number of creep and shrinkage models (GL2000 and CEB). They agree better with the existing code compared with the draft.


 

RE: Creep Shrinkage in Draft AS3600

Couldn't be that contractors have 'gotten to' the code writers in order to shorten construction time?  

RE: Creep Shrinkage in Draft AS3600

Hokie66,

They definitely did not "get at" me!
After the fights between the main committee and certain industry groups over many parts of the new code, I do not think anyone could think that any of those doing the main developemnt work on the code are open to influence, or we would have had a new code 3 years ago!!

Ian does not have time to compare them at the moment as he is one of the main organisers of the CIA congress starting Thursday. But does not think there is a big difference.

The formula is very similar to the Eurocode one except for 1 factor which is not a function of time. Compared to what I use in RAPT for AS3600, for the old version we used loadedperiod to a power of .7. In the new code it is to a power of .8, so there is a difference, but I do not think it is much as you suggest.

Looking at the table in the current code, for 200 thick with an interior environment, 30 year factor is about .75 and the 100 day factor is about .35, so the 100 day figure is pretty close to 50%.

RE: Creep Shrinkage in Draft AS3600

rapt,

Will await those results.  I haven't done any numbers myself, but asixth is normally on the money, and degenn sounds like he knows what he is talking about.

Based purely on observation, I have thought that the existing estimates of shrinkage rates were too fast, so if they are being further accelerated, I for one won't be using them.

Someone on this site recently posted a plot of ultimate shrinkage vs age for various slab thicknesses.  I can't remember the source, but will try to find it and reference it here.  This plot showed about 12 months for 50% shrinkage of a 200 slab.  

RE: Creep Shrinkage in Draft AS3600

I wouldn't say I'm normally on the money, I still get them wrong more often than I get them right.  

RE: Creep Shrinkage in Draft AS3600

Does anyone know the status of the new code. I heard that there are some factors that are still being debated and has pushed the release date back to January?

Not that I am keen to get a new code release, I think the '01 code is a relevant document. Despite the debate over development lengths, high-strength concrete and Clause 8.2.12.4.c.

RE: Creep Shrinkage in Draft AS3600

asixth,

As far as I know nothing is being debated in the code committee. It is finalised as far as they are concerned.

I am not sure if there is any holdup with the Building Control Board. I will see if I can find out.

No matter when it is released, it willl not be referenced in BCA until at least 2011!

RE the existing code, any section that you now know to be unconservative (eg development lengths for small bars), you should no longer use (legally). You should use the new code rules in these areas. Plus the new code now defines rules for things not covered in the old code, like ties in columns with concrete strength greater than 50MPa which night be useful if anyone is actually designing a tallish building in the current economic climate.

RE: Creep Shrinkage in Draft AS3600

I have to get a new name or reduce my ego, when you write RE I always think you are using my initials.

It could be like the amendment to the wind code, the committee ticked this off more than three years ago i think, but for some reason it still hasn't been published.

yes there was a very good article in some magazine a while back about a designer from Germany that got done for not using the most up to date information for design from his knowledge bank. Given he was a part of the committee, but still worth the consideration.

I have been using the draft code for designing truss-ties models since it was published, since it was a lot better than the AS3600-2001

Arguing with an engineer is like wrestling with a pig in mud. After a while you realize that them like it

RE: Creep Shrinkage in Draft AS3600

CIA latest email "Concrete Institute of Australia has been advised by Colin Blair, Deputy Chief Executive, Standards Australia, that AS3600-2009 will be published by the end of October 2009"

Arguing with an engineer is like wrestling with a pig in mud. After a while you realize that them like it

RE: Creep Shrinkage in Draft AS3600

AS3600 - 2009 is delayed apparently by ACBC who have to give a final approval. I have not been able to find out the reasons for the delay but will in the next week or so.

My contact has suggested it may not be out until the end of the year, so it still may end up being AS3600 - 2010!!

RE: Creep Shrinkage in Draft AS3600

Dyslexia strikes again.

That should have been ABCB, Australian Building Codes Board!

RE: Creep Shrinkage in Draft AS3600

Rapt,
Since you have contacts in the right places, can you Please find out what they did with the wind code revision at the same time?



 

Arguing with an engineer is like wrestling with a pig in mud. After a while you realize that them like it

RE: Creep Shrinkage in Draft AS3600

Are they revising the wind code?

RE: Creep Shrinkage in Draft AS3600

I just went and checked the SAI website and there is a draft for comment, thus I assume they decided to do away with t amendment and go to a complete revision. Maybe Woolcock will be able to publish his book revision to the portal frame book next year.

Arguing with an engineer is like wrestling with a pig in mud. After a while you realize that them like it

RE: Creep Shrinkage in Draft AS3600

RE and asixth,

Yes, there is a new draft of the wind code out for comment. They had extra changes they wanted to introduce eg wind pressures inside buildings such as on partitions etc, plus some others that they decided were too much for an amendment so it is going to be a new code release instead. So now you will have to pay for a new copy!

The draft is available fro download for those who want to see what has changed and possibly comment.

 

RE: Creep Shrinkage in Draft AS3600

Rumour has it that AS3600-2009 will indeed be released in 2009, hopefully by the end of November. Apparently the probl;ems from ABCB are editorial and will be finalised quickly. But it will still not be referenced in BCA until at least 2011!

RE: Creep Shrinkage in Draft AS3600

You weren't still there when they announced that today were you, must have given you the inside running before the rest of us.

By the sounds of things I think the committee has got the sh*ts with SAI-Global.

There was talk of emulating ACI and crating the code through CIA, Which I can see no reason for exploring.

 

Arguing with an engineer is like wrestling with a pig in mud. After a while you realize that them like it

RE: Creep Shrinkage in Draft AS3600

I agree, and I like the set-up that ACI has with sub committees (eg Creep and Shrinkage sub-committee, Carbon Fibre sub-committee, detailing sub-committee, FE sub-committee just to name a few). I also enjoy the ACI publication "Concrete International", I find it very helpful with the bi-monthly CRSI "Detailing Corner" and the regular Q&A postings.   

RE: Creep Shrinkage in Draft AS3600

Rowingengineer/Asixth

I left at afternoon tea.

I had written a great response to this and it crashed in the sending, so I will give a summary of it as I am not writing it all again (not happy!!!)

Yes, they are unhappy but with Standards Australia, not SAIGlobal. This has been developing for several years because of the problems with getting this code out. And it has been caused by some groups in the industry (all related to one main group) blocking the code plus the Standards rules on committees and consensus. Standards stuffup with its finances and future codes has not helped (wonder where all of the money went, it was not all to the GFC from what I hear (ever heard of BONUSES!).

Standards Australia has suggested different ways of funding/developing future versions of AS3600. CIA, ACI and EC2 were 3. Another was Standards Australia with monetary support from industry (eg CIA so why not do it themselves as most of the current committee are CIA members and doing it for nothing, not even airline fares and accommodation are paid).

If it was done by CIA it would be the same as ACI doing it for USA!

Noone on the current committee wants to adopt ACI or EC2 as they would need to be modified significantly anyway, and because of the way AS3600 is written, it is based on a lot of testing and developemnt that has gone into both of those codes plus other work. In fact, AS3600 is probably the best of the 3 because of that. Unfortunately it is not as advanced as it could be because of the problems above which have delayed future development.

All 3 codes are developed by a main committee with a sub-committee structure under it. There is no real difference in the way they work except that the chair of the main ACI committee gets to pick his committee, as distinct from AS3600 where the chairman gets who he is given by Standards Australia! In both cases the chairman of each subcommittee can put anyone he wants on a subcommittee and any main committee member can also join. There are good and bad points to both methods. A combination would be best!

EC2 is actually a model code and each country using it rewrites it anyway!

ACI has lots of testing and development work behind it. It is amazing it is such a bad code (in my opinion) considering this! But anything developed by a committee will always have problems.

I do not see what Concrete International has to do with this discussion about codes. It is unrelated and has gone downhill a lot over the years. The ACI Journal has a lot better articles as far as I am concerned and are in many cases reporting the research the ACI code is based on.

CIA also puts out a technical magazine. Does this make it eligible to produce a code also!

RE: Creep Shrinkage in Draft AS3600

No doubt the immediate frustrations with AS3600 are directed at Standards Australia, but it seems to me that the root cause of many of the current problems is the strange system where Standards Australia (through a large band of unpaid volunteers) does all the work and the public listed company SAI Global gets all the reward.

The current issue of Engineers Australia has a letter jointly signed by many current or past chairs of Standards Australia committees (including several current members of BD2), expressing concern about the funding situation at Standards Australia, and looking for a more active role from Engineers Australia.

The director of Engineers Australia (Martin Dwyer) responded positively to this suggestion, but the question remains of how any organisation, whether it be Engineers Australia, CIA, or someone else, will fund the preparation of new standards when they are legally obliged to hand over their work for zero recompense to an organisation that exists for the purpose of making profits for its shareholders.

Doug Jenkins
Interactive Design Services
http://newtonexcelbach.wordpress.com/
 

RE: Creep Shrinkage in Draft AS3600

IDS,

As I understand it, Standards Australia came up with the brilliant idea to sell the rights to print and sell all Australian Standards documents to SAI Global for (I think) a period of 20 years.

So SAI Global has paid for these rights. Something in the order of $250,000,000 as I understand it. This was then invested (less some significant bonuses paid to those brilliant people who organised the financial windfall for Standards Australia!). Standards Australia were then supposed to use the proceeds of this "sale"/contract, plus the interest/dividends from investing it, to fund its operations for the term of the contract, 20 years.

It is apparently down to closer to $150,000,000 now and is not sufficient to fund continuing operations like writing new standards to control every aspect of our lives like they have over the last few years (to increase their market and make themselves more valuable) and to pay their bloated burocracy.

Whether or not the above had happened, everyone on committees has been doing it for free since 1932 or whenever Standards began to be developed in Australia, supposedly because of their altruistic nature. The only difference is that, Previously Standards Australia made the money from each sale of a printed document, whereas now it has been paid upfront for the sales for the next 20 years.

So it is not SAI Global's fault as such. Standards Australia got themselves into the mess all by themselves. It is their rights contract and management of the money from the sale of this rights contract that has caused the problem.

They should be thrown into jail with the USA merchant bankers. They have basically made the same mistakes and ripped off us, the end user/taxpayer.

The only solution would appear to be a government bailout or an industry by industry bailout by each industry funding its own standard development, the sales rights to which still belong to SAL Global for 20 years, because legally, Standards Australia is currently the only body allowed to produce Standards Documents and they must be sold through SAI Global because they have already paid for the right to sell them!

So presumeably, we as an industry have to fund the development of the next AS3600 (committee members have been doing it for years, now everyone has to) and then pay for a copy of the final document as well or SAI Global might sue and consequently shut down Standards Australia for breach of contract. And that might be the best solution in the end!

RE: Creep Shrinkage in Draft AS3600

(OP)
I think a new thread is needed as we've changed subject!

I think some of the ideas raised at recent AS3600 conferences for a blog or faq site is perhaps a step in the right direction to resolve the problems of getting a formal code out in a timely fashion. Any thoughts?

RE: Creep Shrinkage in Draft AS3600

degenn

I will post my excel macros for the creep co-efficients and shrinkage strains when the new code is released so we can discuss how the two models compare to each other.

RE: Creep Shrinkage in Draft AS3600

Cheers Doug

I have never seen that site before, it looks like it has some good stuff in it.

RE: Creep Shrinkage in Draft AS3600

(OP)
Thanks for the reply Doug.

Your spread sheet has EC2 at 50% complete at 120 days where the draft has 50% complete at 60 days for a 200 slab.  

RE: Creep Shrinkage in Draft AS3600

degenn - yes, I don't know the details of the research behind the numbers in the new code (or if the numbers will be the same in the final code when it is released), but the EC 2 numbers would be based on much older research, with older cements.  

I also note that the creep at one day is much higher in EC 2 than in AS 3600.  If anyone knows the detailed background to these changes I'd be interested to hear it.

Doug Jenkins
Interactive Design Services
http://newtonexcelbach.wordpress.com/
 

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