Concrete effective width - Composite Bridge

Hi everyone,

I’m modeling a composite bridge to run modal analyses and understand the natural frequencies of the bridge and I need some advice.

I’m using a beam model with a composite thin walled section and I’m wondering whether the effective width of the concrete is calculated automatically by aqua. From a few tests and the manual I’d understand it does, but how?

Also, in one of the tutorials it is suggested to use a shear connection with a width of 100mm between the top flange and the concrete, what is the range that can be used and why 100mm is suggested?

A big thank you to everyone that can help with this doubts :slight_smile:


Hello Giorgia

The effective width of a T-Beam or a composite beam is not calculated automatically. The width of the cross-section is processed as the effective width. Therefore please calculate the effective width according to your design code by hand and set the width of the concrete plate as wide as the effective width.

The width of the shear connection depends on its use case. Further information can be found in the AQUA manual:

SSD / TEDDY > Help > User Manuals > AQUA > chapter 3.40 WELD - Shear Connection

If you require more information about the modelling of the composite cross-section, look at the following two TEDDY examples.

TEDDY > File > Examples > AQB > english > composit.dat
TEDDY > File > Examples > AQB > english > composit_neff.dat

Best regards
Frederik Höller
Your SOFiSTiK Support Team

Thank you for your reply Frederik,

Oh ok, I misread the manual and the small variation in eigenvalues for my bridge, thank you so much for the explanation. So it is the same for Class 4 sections, correct?

I’d have another question about the shear connection. I read that “- Shear bonds in composite sections (T < 0)” on manual AQUA > chapter 3.40 WELD - Shear Connection. But I’m using Sofiplus, and from the tutorial I saw the use of 100mm. So is that value somehow related or do I just need to vary it until I get “good” values?

Best Regards,

Hello Giorgia

For the non-effective areas of cross sections class 4, you could have a look at the two examples:

TEDDY > File > Examples > AQB > english > section_class4.dat > Infocenter - Overview > Documentation - Tutorials > Design of steel structures > Cross-section class 4 concept

Now to your second question.
If you increase the absolute value of T, you increase the stiffness of the shear connection. This means that a large |T| represents a nearly rigid connection. I can’t tell you which value is optimal for your project, because it depends on your system.
The sign of the effective thickness T controls, if the shear forces is calculated in dowels or welds:

  • T < 0: calculation of shear bonds in dowels
    -> Graphic > Design > External Beam Sections > Stress of material > Shear in dowels/welds
  • T > 0: calculation of shear in welds
    -> Graphic > Design > External Beam Sections > Stress of material > in welds

Best regards

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Thank you for your replies Frederik!