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reinforce existing steel beam - section definition

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Message 1 of 21
dimogrec
2172 Views, 20 Replies

reinforce existing steel beam - section definition

Hi I would like to reinforce an existing steel beam (IPE 400) by welding a cover under the bottom flange (i.e. a 200X14 plate). To model this case I initially used a section defined by me in the section definition (importing an IPE400 from database and then adding a the plate under the bottom flange) and I also clicked on standardization and gave it a name of IPE_40.

I also created,in section definition, the same beam with above, but without using standardization and I saved it with the name IPE_400X14X14.

To be honest I did not pay attention to the  dimension numbers (dimension 1 2 3) and section type that I used to save the section on database. I thought it isn't important. But I noticed strange results on member verification...

In example for the section IPE_400X14X14 (always an IPE400 with a plate 200X14 under the bottom flange) I saw in the calculation results of section definition a Wply=1600cm3 or something like this , but in the steel design of the member I notice a Wply=2482cm3. Also tf and tw are not as defined and finally this section is checked for shear and not for bending moment

Strange mechanical properties also for the member IPE_40 where I notice a Wply=4704cm3 (!!!) where in this case leads to a very high Myplrd and also fy=215Mpa and fu=340Mpa as if it was a thicker steel, maybe because it takes into account a tw=8.6cm.I also see different Ay and Az in results of steel design and object inspector

Finally I defined a new section (not in section definition) as special SFB414-IPE400+200X14 which seems to work fine in steel design

1) is it right to use SFB414-IPE400+200X14 to model and design my case or is there e better way?

2) How saving to database alters the results in steel design (in terms of section properties)? I mean which is the proper way to save a section defined in section definition and keep the values of properties calculated in section definition?

3) What is standardization, when should I use it?

4) It would be nice to be able to see all the mechanical properties in object inspector instead of zero values.

5) in section definition, complex section definition C17 I'm not able to get the desirable length (see picture).

thanks in advance

20 REPLIES 20
Message 2 of 21
Rafal.Gaweda
in reply to: dimogrec

Send also your user database where these section are saved.



Rafal Gaweda
Message 3 of 21
dimogrec
in reply to: Rafal.Gaweda

Hi Rafal,

Do you mean Ruserpro.xml?

Because when I click File->Import from database-> User I can see both IPE sections created by me, but when I click Tools->section database and then open existing -> Rusepro.xml , only default section "test 4X8X0,5" appears.

Message 4 of 21
Rafal.Gaweda
in reply to: dimogrec

So there must be a few ruserpro.xmls on your disk,

Search for them and find the valid one.



Rafal Gaweda
Message 5 of 21
dimogrec
in reply to: dimogrec

Yeah... really a lot of ruserpro.xmls... finally I found the right one Smiley Happy

Message 6 of 21
Rafal.Gaweda
in reply to: dimogrec

First look: difference in red

 

ipe400x.jpg



Rafal Gaweda
Message 7 of 21
dimogrec
in reply to: Rafal.Gaweda

Yes, these differences are generated because of saving to database... As I wrote above, I didn't pay attention to dimension 1, dimension 2, dimension 3 and section type when saving to database. (I thought they were only some kind of description) Those values, as I undertsood later, are taken into account at steel design (verification of the member) that's why I made the question 2)

Message 8 of 21
Rafal.Gaweda
in reply to: dimogrec

Dim1 Dim2 Dim3 files are used only to generate "full" Section name.

You can use them or not ; your choice what values can be written there.



Rafal Gaweda
Message 9 of 21
dimogrec
in reply to: dimogrec

thanks Rafal

...while "section type" and its parameters (h,b,tf,tw....) are used for steel design, am I right?

Message 10 of 21
Rafal.Gaweda
in reply to: dimogrec


...while "section type" and its parameters (h,b,tf,tw....) are used for steel design, am I right?


Yes.

I mean instead of h and b    vy+vpy vz+vpz are considered accordingly.



Rafal Gaweda
Message 11 of 21
dimogrec
in reply to: Rafal.Gaweda

Thanks again Rafal

could you also explain me what does "standardization" do and when should I use it?

 

Also one other note.Even if in help page it's written that you cannot design SFB-section members in Robot, when I proceed to steel design of an SFB section I get no warning message for that...

Message 12 of 21
Rafal.Gaweda
in reply to: dimogrec


could you also explain me what does "standardization" do and when should I use it?

 

It merges overlapping contours into one (if they have the same material)

 

Also one other note.Even if in help page it's written that you cannot design SFB-section members in Robot, when I proceed to steel design of an SFB section I get no warning message for that...


I tried your file from first post and it works.



Rafal Gaweda
Message 13 of 21
dimogrec
in reply to: dimogrec

Yes it works, that's what I also wrote, and since it's written in help page that you cannot  design SFB sections I was expecting to get a warning message that I cannot design such members.

Anyway supposed that it works I believe that section classification is not as expected. Robot treats the section in example (SFB IPE400 + 200X14, IPE 400 with a plate 200X14 on bottom flange) as section class 1 so Mrd=Mpl but in my opinion the section is class 3 (because of the web).

Message 14 of 21
Rafal.Gaweda
in reply to: dimogrec

The web has a slenderness of 38.5.
The element is only bent by moment so we are setting slenderness limit according to column 1 Table 5.2

 

sle.jpg

 

Slenderness Class 1 with coefficient E = 1.0 is 72
Thus, the web slenderness 38.5 <72 which means first class

 

This profile will be Class 3 for pure compression - see column 2
Slenderness limit for Class 2 is 38 so it goes into the Class 3



Rafal Gaweda
Message 15 of 21
dimogrec
in reply to: Rafal.Gaweda

Thanks Rafal for your time

I would agree with what you wrote if it was for a (bi) symmetrical section. In my case it's an asymmetrical section. The first diagrams we see  (for sections class1 and 2) in the sheet 1 of table 5.2  refer that any fiber of the section has reached fy, (that the section is fully plasticized). That's also the capacity of these sections. So if you want to find out the class of the section first of all you need to know the plastic neutral axis and then use one of the  first 3 diagrams (depending on the position of the plastic neutral axis). The table refers to parts of section, in this case web. If the section is under bending doesn't always mean that also the web has only bending.... at least that's what I presume, I hope I'm not confused.

In my case, doing what said, I found that the plastic neutral axis is located far below the "center" of the section so using the  third column of the table I found that it's not class 1 or 2.
 Then jumped to "triangular" stress diagram (and this time elastic neutral axis) found ψ and found that web is class 3.

Please let me know if you have different opinion (or anyone of the forum members)

p.s. it's not urgent

 

sect_class.jpg

Message 16 of 21
Rafal.Gaweda
in reply to: dimogrec

Unfortunately 😞 you are right.

We need to correct it.

Thanks for deep check.



Rafal Gaweda
Message 17 of 21
Tuctas
in reply to: Rafal.Gaweda

Finally, Robot makes the design of SFB sections...

Is there any update-correction about the classification of such sections?

 

Message 18 of 21
Artur.Kosakowski
in reply to: Tuctas

Done for Robot 2015.



Artur Kosakowski
Message 19 of 21
dimogrec
in reply to: Artur.Kosakowski

Hi Artur, are you sure about the correction?

1) I'm using RSA16 and I would expect the above section to be class 3 but robot calculates it as class2.

I think the problem is in α (alfa) calculation or in plastic neutral axis position.

If I assume that my calculations are correct and the position of pna is as shown in my previous post, then the only reason to get α=0,93 is that Robot does not take c=33,1cm as it should for claculations (for IPE400) but a higher value (maybe c1=(d-c)/2 +c where c=33,1, d=total height of web=37,3cm so (d-c)/2 + c = 352cm. in this case α=328,2/352=0.93).

So please do a check for this.

2) In the help page of Robot 16  is written that Currently, you cannot design SFB-section members in Robot

help page

3) It would be great having the position of plastic neutral axis in the section definition results.

Thanks in advance

 

class.jpg

Message 20 of 21
Artur.Kosakowski
in reply to: dimogrec

Robot follows CTICM recommendations for calculations of the position of the netural axes which in turn inflences the value of alpha.

 

CTCIM.PNG

 

If you find your post answered press the Accept as Solution button please. This will help other users to find solutions much faster. Thank you.



Artur Kosakowski

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