Steel Design to AS4100

[tony.ridley]

Hi, another question on steel design to Australian code;

In all of the steel beams in the Australian steel database, I cannot find a value displayed for Iw (warping constant). 

When I perform steel design check, the results do not display Iw anywhere. 

Background:

In accordance with 5.6.1.1 of the code, alpha s is calculated using the reference buckling moment (Mo).  To obtain Mo, you need Iw, unless you conservatively choose Iw to be equal to zero.

When I cross check Robot output with my hand calculation (which has the correct Iw), I get the same answer for alpha s and also Mo and Mb.  If I use zero for Iw, I get different results to Robot.  This tells me Robot is using the correct Iw, but I just can't see where it is!

Question:

1. How is alpha s calculated in Robot?  Does it use Iw, or does it assume Iw = zero?
2. If robot is using Iw correctly (seems it does), then why can't I see what Iw is?
3. Why does Robot not consider Mo, Mb, alpha s for minor axis bending?  i.e. Why does Robot not perform lateral buckling check for minor axis bending. 

Thanks again,

Tony

[tony.ridley]

Update,

I have found in the xml file,

C:\ProgramData\Autodesk\Structural\Common Data\2013\Data\Prof\Auspro.xml

So it seems Iw is in there, just not displayed anywhere.  Can it be displayed please as part of the next SP release?

Also, can terminology be changed?  For example, can Ix be renamed to J ?  Can i do this myself by editing the .xml files?

Tony

[Artur.Kosakowski]

Please send me the rtd with this beam. I'd like to have a look at it as I'm not sure if Iw is actually IX (IX is used for all databases or shall I write section properties (similar to IY and IZ and this is not planned to be changed). My assumption is that Iw should be available on the detailed tab of the code check results as this is the value calculated inside the steel design module itself.

[tony.ridley]

Artur,

No, the value displayed in object inspector Ix is actually written as J inside the steel design results (but exactly the same value). 

I have since found that Iw is stored for the beams, but just ot displayed anywhere, not even in the detailed steel design results.  The only place I can find it is in the .xml file. 

Tony

[Artur.Kosakowski]

I'm sorry for my limited knowledge of AS4100. At this moment my assumption is that AS names J what in Robot database is named IX and the steel calculation note uses J as well ( I assume that this is correct). On the other hand Iw (which is different than IX or J ) is internally calculated inside the steel design module but not displayed in the note (which is the request for the next versions of Robot). I'll check that and your questions from the first message but I will not be able to do this before the end of the next week.

[tony.ridley]

Thanks,

Yes, your assumption is correct.  

However Iw is not "calculated", but is stored in the section file.  Only need to "show" this value, thats all.  

And yes, Robot should be considering minor axis Mb as well.  

Cheers,

Tony

[Artur.Kosakowski]

Could you send me your test file please? Thank you.

[tony.ridley]

File attached,

See pics;  alpha s is there, but not Iw.  You can't get alpha s without Iw. 

Also, no alpha s for Mbz, only Mby

Thanks,

Tony

[Artur.Kosakowski · Accepted solution]

To sum up:

Question:

How is alpha s calculated in Robot?  Does it use Iw, or does it assume Iw = zero?

Iw is calculated

If robot is using Iw correctly (seems it does), then why can't I see what Iw is?

The request of adding this information to the detailed results note has been added to the wish list.

Why does Robot not consider Mo, Mb, alpha s for minor axis bending?  i.e. Why does Robot not perform lateral buckling check for minor axis bending.

That is in general not done (for any design code). I'm not aware of any code provisions for lateral buckling of e.g. I section when load is applied in the direction perpendicular to its web.

Ix from Robot section database is J from the AS code (and as such (J) is displayed in the calculation note).

[tony.ridley]

Thanks,

[tony.ridley]

Hi,

I just checked RSAP 2015 SP3 and the Iw still has not been added to the steel design output for AS4100. 

Is it possible to add it soon?

thanks,

Tony

[Artur.Kosakowski]

Added in SP1 for Robot 2016.

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