Since the previous post, I have updated the notes in the RC Design Functions spreadsheet to reflect the fact that with the recent update to the Bridge Design Code (AS 5100) the reinforced concrete strength design requirements for beam bending and combined bending and axial load are now the same as in AS 3600. The updated spreadsheet can be downloaded from:

RC Design Functions7.zip

The RCInteract function will generate a moment-axial load interaction diagram to a number of design codes. For AS 3600, and now AS 5100 as well, it will also adjust the results according to the specified confinement steel.

The screen shot below shows input and plotted results for 65 MPa concrete to AS 3600 including the effect of compression steel (blue line), and with compression steel ignored:

If the confinement option is set to 1 the compression steel is included for axial loads <= 0.5Phi.Nu:

Confinement option 2 applies the AS 3600 limitations for standard confinement to Cl. 10.7.3, for concrete grades >= 65 MPa:

Confinement option 3 gives results where special confinement to Cl. 10.7.3 is provided, i.e. compression steel is included for all axial loads.

The function input is (arguments in italics are optional):

RCInteract(UMomin, *PRange, NSteps, Muin, Code, CompFace, AxLoadA, Confinement*):

- UMomin: Section details (Range D4:D16 in the example data)
*PRange:* Axial load range; default = 0 to Phi.Pu
*NSteps:* Number of output increments; default = 20
*Muin: *Array of moments for each axial load, defining the compression face; default = use CompFace
*Code:* Design code; default = 1 = AS 3600 and AS 5100-2017
*CompFace:* Compression Face, 1 = top face, anything else = bottom face; default = 1
*AxLoadA: *Array of output axial loads; default = use Prange and NSteps
*Confinement:* Confinement option (Code = 1 only); default = -1 (include compression steel for all loads)

Output is an array with 3 or 1 columns, depending on whether AxLoadA was specified; see below:

To display all results the function must be entered as an array function, by selecting the required output range and pressing Ctrl-Shift-Enter. See Using Array Functions and UDFs for details.

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I cant find anywher your DepthNA.pdf

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Try:

Click to access rc-na-depth.pdf

and

https://newtonexcelbach.wordpress.com/2008/03/25/reinforced-concrete-section-analysis-1/

Is that the one you are looking for?

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Thanks, but I was after the DepthNA.pdf, that I assume has the prestress steel as well

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DepthNA.pdf and rc-na-depth.pdf are actually the same file, I forget why I gave them different names.

I couldn’t find anything on the blog about how the prestress is handled, so I’ll add something when I have time, but in brief the prestress is converted to an axial force and moment, which is added to the applied load, and the analysis then proceeds as for a section without prestress.

By the way, where did you find the reference to DepthNA.pdf?

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Thanks…

The reference to DepthNA.pdf, appers on your “Beam Design Fuctions.xls, Ver 1.04, under the Contents. It Notes:

‘Details of the analysis are provided in the file: DepthNA.pdf, which may be downloaded from: https://newtonexcelbach.wordpress.com/

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Dougaj4,

What I was really after is a Cross Section program that caters for passive reo and prestress tendons, under an applied moment and axial force

The program should do a working stress analysis, and calculate the Transfer Condition and then the cracked section condition.

The program should give initial and incremental stresses in the concrete, passive (positive and negative) reinforcement, and the tendons. All as required by AS3600 Clause 8.6.2

Also the software should do an Ultimate capacity check

Can your spreadsheets be adapted to do this?

Thanks in advance

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For the time being you can get the information you need from the Beam Design Functions, but you’ll need to do it in a couple of steps:

– Find the applied moment that has exactly zero stress at the tension face, using goal-seek.

– Copy the stresses you need to any convenient location.

– Enter the SLS moment to find the stress increment.

Note that columns C and D (on the Elastic1 Out sheet) give the stresses and strains for the outer layers of reinforcement only, but columns L and M list the stresses and forces for every layer, from top to bottom.

It will be quite straightforward to add this calculation to the function output, so I’ll do that in the next version.

For ULS you need ULS Design Functions.xlsb

Please let me know if that all makes sense, or if you have any more questions.

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Thanks, but……I’m new at this

If not too much to ask, can you do this on your current Beam Design Functions.xls example?

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OK, I’ll try and get something up in the next few days

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Steven – see:

https://newtonexcelbach.wordpress.com/2017/07/02/stress-increments-in-prestressed-concrete-beams/

Any questions, please ask.

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Hi Doug, in what situations are confinement options 0 & 1 used?

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See AS 3600 Cl 11.7.4

When designing a wall to the column provisions of Section 10, Cl 10.7.4 (restraint steel) does not apply if N* <= 0.5.phi.Nu, or if the compression steel is ignored (and f'c <= 50 MPa).

Option 1 covers that case.

Option 0 is a more conservative application of that clause, or can be used to find the difference that the compression steel makes.

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Thanks very much. And confinement -1 is functionally the same as confinement 3?

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Yes, confinement 3 includes the compression steel for all axial loads and concrete grades, so it is the same as -1.

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Thank you very much for the amazing work.

Do you have a function even for the ineraction diagram of circular sections?

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The spreadsheet here:

https://newtonexcelbach.com/2012/08/09/uls-analysis-of-concrete-beams-now-with-added-units/

will do an interaction diagram for a circular section (or any other shape) by dividing the cross section into trapezoidal layers.

The RC Design Functions spreadsheet has a function for elastic analysis of circular sections (Circe), but not yet anything for ULS capacity of circular sections.

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