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  1. IDS

    box culvert analysys

    Precast concrete arches are perfectly practical for a buried arch of that size, and they have the added benefit that the supplier will do the design. Disclosure: I used to work for Reinforced Earth (now Geoquest) who supply the TechSpan arch system, and they are now my biggest client.
  2. IDS

    What is this Rm line in this biaxial interaction chart - Eurocode 2

    I've been busy updating my biaxial bending spreadsheet, I'll post a link here when I publish it. I think the text you posted is clear enough about what Rm is. For instance, if you had a design bending moment of 40% of the maximum bending capacity, you could look at where the Rm = 0.4 line...
  3. IDS

    What is this Rm line in this biaxial interaction chart - Eurocode 2

    I don't know what the Rm lines are for, other than that they seem to be related to the balance moment, which affects the capacity reduction factor calculation in some codes (but not Eurocode 2). How does the book say it is calculated? Incidentally, if I search for Deep Surface and the authors...
  4. IDS

    One Drive - Am I the Last Person Using Dropbox for Business

    I use Onedrive because you get plenty of space as part of Office and it's reasonably easy to use, although there are plenty of things I don't like about it. I briefly used Dropbox when it first came out, but I really dislike it and try to avoid it as far as possible. I'd say the majority of...
  5. IDS

    Why are neutral axis different when checking ultimate moment and cracked inertia?

    Neither of those calculations have anything to do with bending moments. For a rectangular stress block with a specified stress the force in the concrete = stress x area. For a linear-elastic stress block we don't know the stress, but it is proportional to the distance from the neutral axis...
  6. IDS

    N-M interaction chart to Australian Standards

    You should absolutely assume everything you read in this forum is wrong, until proved otherwise. But the same applies to "official sources". As for sources of information, rather than accepting numbers presented in chart form in a book I think it is better to work through calculation examples...
  7. IDS

    N-M interaction chart to Australian Standards

    Sorry about that, you have to stop somewhere. CSA does get a mention in this one: https://interactiveds.com.au/Publications/Shear%20and%20Torsion-CIA-2023.pdf
  8. IDS

    N-M interaction chart to Australian Standards

    What is the point of referring to old charts that will have different results to the current code? Also being printed in a book does not make a chart "official".
  9. IDS

    N-M interaction chart to Australian Standards

    I don't know of any printed interaction diagrams for the latest AS 3600, but you can always use the RCInteract function from my RC design functions spreadsheet, which you can download from: https://newtonexcelbach.com/2025/02/08/rc-design-functions-9-07/ Also see...
  10. IDS

    N-M interaction chart to Australian Standards

    The interaction diagram shown is not for biaxial loading. The examples in the book find the capacities about the X and Y axes, and then combine the ratios of applied moment to moment capacity, using the code simplified approach. The Australian code (AS 3600) has procedures for finding the...
  11. IDS

    Bi-axial bending chart - concrete column

    We are starting to go round in circles here, but: It's "acceptable" in the sense that it will always be conservative, and will give the correct result when M = 0, but I don't see the point of doing complex calculations with a lower than required limit on the strain, when a straight line...
  12. IDS

    Bi-axial bending chart - concrete column

    Frankly I am not sure how cl. 6.1(5) is supposed to be applied, but since we are not analysing a flanged beam it doesn't seem relevant anyway. There seems to be general agreement, both in the post above and in the other thread you started here, that as the NA goes from just outside the section...
  13. IDS

    Should there be a dip in my N-M diagram or not - Eurocode - concrete columns

    Retrograde - I agree. This is the reason we are still getting different results in the other thread.
  14. IDS

    Bi-axial bending chart - concrete column

    No, we aren't over-estimating the in-between points. The curve if you did the calculation would be slightly convex, so a straight line would be slightly conservative, but the difference is very small. You only get the step in the line in your graph because you insist on reducing the strain at...
  15. IDS

    Bi-axial bending chart - concrete column

    Yes, why do you think you need to do anything else? The whole section has the same strain and stress, so just multiply by the areas to get the force.
  16. IDS

    Bi-axial bending chart - concrete column

    Full calculation? Sure: Force = Concrete stress x concrete area + (Es x 0.00175 - concrete stress) x steel area. All forces are symmetrical about the concrete centroid, so moment = 0.
  17. IDS

    Bi-axial bending chart - concrete column

    What do you understand by "pure compression"? My understanding is that the compression strain is constant across the section, so the bending moment is zero. Under that condition the strain limit applies across the full section. When the NA is at the base of the section the strain distribution...
  18. IDS

    Bi-axial bending chart - concrete column

    Yes, the strains are just for the calculation of the steel stresses. The stress for the rectangular stress block is defined in the code, and it doesn't say anywhere it should be reduced for sections with uniform compression. The code also does not say there should be a jump in the strain at...
  19. IDS

    Bi-axial bending chart - concrete column

    Have another look at Fig. 6.1 in the code: - When the bottom face is in tension the top face strain stays constant at 0.0035 - When the NA reaches the bottom face the top face strain is still 0.0035, the bottom face is zero, and point C is 0.00175 (or 0.002 for the parabolic stress block). - For...
  20. IDS

    Bi-axial bending chart - concrete column

    The text doesn't say anything about the 0.9 factor, so we can assume they didn't apply it. The charts are for rectangular sections bending about their principal axes, so there is no reason why they would have applied it. My calculations fitting the chart also did not apply it.

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