Strut Tie Modelling in AS3600
Strut Tie Modelling in AS3600
(OP)
Nathan,
Replying to your queries below
- No mention on hot to resolve tangential shear stresses on the node. We need to refer to Stephen Foster presentation to have clarification on this
AS3600 is not a text book. It defines limits on the design methodology. Read a good text book on the topic, or Stephen Fosters presentation if you want.
- In the ACI the development of the tension tie start when the tie meet the concrete strut which make sense because in that region the concrete is in compression as such the tie is confined. Developing the tie before the node allow to have less congestion where the node is.
You cannot logically start the development before the node. The whole logic is that the full tension force reaches the node! There is a further argument that the development should start behind the node, past the end of the compression zone. ACI obviously does not agree, but that does not make them correct!
- Code does not cover confinement of the node if the node is overstressed. What do we do to confine the node? Follow the recommendations for columns?
This is covered in the new Commentary that hopefully will be released soon!
- Bursting of struts for pilecaps? Do we need bursting reo or not? I went to a conference and the lecture mentioned that bursting reo is not required for pile caps, however the core doesn't talk about this.
The Strut Tie chapter in AS3600 (chapter 7) is a general set of rules for the design of strut-tie and ties and their connections.
Pile Caps are a specific application which should be covered in Chapter 12, Design of Non-Flexural Members, but is not covered specifically. So I assume you will have to use some engineering judgement in deciding how to design it, or again refer to text books. But I do not think you can apply a single rule for all struts in all pile caps in this case. I would think it would depend on the arrangement and the location of the compression strut within the pile cap. A strut at the edge could easily burst, while an internal one that is fully confined by other concrete maybe is less likely to burst.
What i meant is that there are a lot of area that are not covered in AS3600. It would be good to have some clarifications.
Again, AS3600 is not a text book. It defines limits on the design methodology. You need to apply engineering judgement in applying the rules as you do for all areas of analysis and design.
Trenno,
Maybe the researcher mentioned is not up to date on S&T and needs to read up on it a little more before making comments like that!
Replying to your queries below
- No mention on hot to resolve tangential shear stresses on the node. We need to refer to Stephen Foster presentation to have clarification on this
AS3600 is not a text book. It defines limits on the design methodology. Read a good text book on the topic, or Stephen Fosters presentation if you want.
- In the ACI the development of the tension tie start when the tie meet the concrete strut which make sense because in that region the concrete is in compression as such the tie is confined. Developing the tie before the node allow to have less congestion where the node is.
You cannot logically start the development before the node. The whole logic is that the full tension force reaches the node! There is a further argument that the development should start behind the node, past the end of the compression zone. ACI obviously does not agree, but that does not make them correct!
- Code does not cover confinement of the node if the node is overstressed. What do we do to confine the node? Follow the recommendations for columns?
This is covered in the new Commentary that hopefully will be released soon!
- Bursting of struts for pilecaps? Do we need bursting reo or not? I went to a conference and the lecture mentioned that bursting reo is not required for pile caps, however the core doesn't talk about this.
The Strut Tie chapter in AS3600 (chapter 7) is a general set of rules for the design of strut-tie and ties and their connections.
Pile Caps are a specific application which should be covered in Chapter 12, Design of Non-Flexural Members, but is not covered specifically. So I assume you will have to use some engineering judgement in deciding how to design it, or again refer to text books. But I do not think you can apply a single rule for all struts in all pile caps in this case. I would think it would depend on the arrangement and the location of the compression strut within the pile cap. A strut at the edge could easily burst, while an internal one that is fully confined by other concrete maybe is less likely to burst.
What i meant is that there are a lot of area that are not covered in AS3600. It would be good to have some clarifications.
Again, AS3600 is not a text book. It defines limits on the design methodology. You need to apply engineering judgement in applying the rules as you do for all areas of analysis and design.
Trenno,
Maybe the researcher mentioned is not up to date on S&T and needs to read up on it a little more before making comments like that!





RE: Strut Tie Modelling in AS3600
rapt,
I think the researcher that Trenno was referring was Prof Mike Collins who toured AU recently on S&T methods. He co-developed the Modified Compression Field Theory. Mike did his PhD in UNSW (I think) but has been at U of Toronto for a long time.
RE: Strut Tie Modelling in AS3600
RE: Strut Tie Modelling in AS3600
RE: Strut Tie Modelling in AS3600
Just because codes use an idealized prismatic strut to do the actual strut calculations does not mean that the compression does not actually spread in a "bottle like" shape as described in the codes (and would show in 3D finite element analysis). In the compression design of the strut, it is conservative to assume the idealized prismatic shape. But in terms of splitting, the bottle shape describes the bursting forces logically.
RE: Strut Tie Modelling in AS3600
http://www.nceng.com.au/
"Programming today is a race between software engineers striving to build bigger and better idiot-proof programs, and the Universe trying to produce bigger and better idiots. So far, the Universe is winning."
RE: Strut Tie Modelling in AS3600
To give a little bit of context he was at the time comparing the Australian and Canadian codes, so perhaps he was a little biased, who knows??
RE: Strut Tie Modelling in AS3600
No offense received.
Technical experts should make sure that they make responsible comments when giving lectures. Apparently Prof Collins is known to be critical of the need to use Bottle Shape struts in design, but that is different to "concrete does not act that way". Concrete does act that way, but you can simplify it in design if you want. The compression design of the strut will be controlled by the smallest width available, which will normally be the width at the node. As you move away from the node, the compression stress reduces as it is spread over a wider width, if that extra width is available, so it is not as critical. But the compression stress will spread if it can. That is the basis of all concrete design when considering concentrated forces.
ACI code shows a bottle shape strut, and superimposed on it is an "Idealized prismatic strut". Eurocode shows curved compression trajectories in its section on transverse tension forces. You know what AS3600 shows. Canadian code implies prismatic struts! But is also requires a grid of "crack control" reinforcement in both faces for the full depth of the member.
RE: Strut Tie Modelling in AS3600
Most consultant drawings that I have seen call up 2 additional tie sets in the pile cap but I think this comes more from securing fixing column bars than anything.
RE: Strut Tie Modelling in AS3600
http://www.icevirtuallibrary.com/content/article/1...
Full paper is 20 pounds to non-subscribers.
I haven't read the full paper yet (I have it downloaded), but the abstract suggests that not only does the Canadian code include requirements for bottle-shaped struts, it is more conservative than the ACI or Eurodode.
Regarding pile-caps, the suggestion that bursting reinforcement isn't required seems strange. Surely it depends on the specific pile cap, and can only be determined by doing the analysis.
For the development of tie-reinforcement, I presume there is considerable research on this. Does anyone have a link to a good paper?
Doug Jenkins
Interactive Design Services
http://newtonexcelbach.wordpress.com/