# Inclined stiffeners

Discussion in 'Class Societies' started by Roni, May 13, 2021.

1. Joined: May 2020
Posts: 30
Likes: 0, Points: 6
Location: Brazil

### RoniJunior Member

I'm working out scantlings in accordance to GL 2012 HSC rules. I was wondering what treatment is usually to inclined stiffeners, such as the one from the image:

Is it usual to calculate the second area moment of the inclined section or just simplify and do the calculations assuming a perpendicular stiffener with the web height and not web depth?

Thanks a lot

2. Joined: Sep 2011
Posts: 7,321
Likes: 683, Points: 123, Legacy Rep: 300
Location: Spain

### TANSLSenior Member

You should calculate properties of the inclinened section. Anyway, in such a rectangular shape, using web height could be enough.

3. Joined: May 2020
Posts: 30
Likes: 0, Points: 6
Location: Brazil

### RoniJunior Member

I've done some quick comparisons and just using the height instead of depth does give a smaller value for I (second area moment) than calculating I value for an inclined section. The larger the angle the greater the difference. I was also looking at the web shear area, and comparing the GL 2012 HSC, wich states in section C3.8.4.1:

The web may be attached vertically or inclined to the
attached shell (only the structural height times the
thickness as effective shear area is to be considered)
On the other hand DNVGL 2019 HSC rules state that:

Where beams are inclined towards the attached plating, see Figure 12, the inclination shall be considered in an appropriate way when calculating the scantlings. Usually the web of a beam is contributing to the full depth of the beam, where the bending stiffness shall account only for a structural height as measured perpendicular to the attached plating.
I know they are different rules, but was nonetheless curious on why the different treatments.

4. Joined: Sep 2011
Posts: 7,321
Likes: 683, Points: 123, Legacy Rep: 300
Location: Spain

### TANSLSenior Member

I think that I do not fully understand what you want to compare, but the shear area is the same, whether the reinforcement is inclined or not, while the first and second moments of area change a lot with the angle formed by the reinforcement and its associated plate.

5. Joined: May 2020
Posts: 30
Likes: 0, Points: 6
Location: Brazil

### RoniJunior Member

If I'm reading the rules correctly the Gl 2012 rules states that I should consider the shear area = depth*thickness (form rule: "
only the structural height times the thickness as effective shear area is to be considered"), while the DNVGL rules states that I should consider the shear area = height * thickness ("Usually the web of a beam is contributing to the full depth of the beam").

6. Joined: Sep 2011
Posts: 7,321
Likes: 683, Points: 123, Legacy Rep: 300
Location: Spain

### TANSLSenior Member

I have always used, and I think it is the right thing to do, the actual area of stiffener.
I think you should forget the GL regulation and use the last one from DNV-GL.

7. Joined: May 2020
Posts: 30
Likes: 0, Points: 6
Location: Brazil

### RoniJunior Member

The actual area of the stiffener does seem more correct and in line with beam theory.

8. Joined: Sep 2011
Posts: 7,321
Likes: 683, Points: 123, Legacy Rep: 300
Location: Spain

### TANSLSenior Member

9. Joined: Jun 2009
Posts: 1,621
Likes: 624, Points: 113, Legacy Rep: 1165
Location: Sweden

### baeckmoHydrodynamics

That stiffener is subject to buckling, it will deform till it lies flat to the skin, unless it has a substantial flange that prevents the top part to deflect sideways. I have seen bottom panels completely "blown inwards" with that kind of "stiffener"; in my world it is to be avoided!

10. Joined: May 2020
Posts: 30
Likes: 0, Points: 6
Location: Brazil

### RoniJunior Member

I'm doing the dimensioning with as an exercise, but went with the L stiffener because local builders in the area said the much rather build that than a top hat.

11. Joined: Sep 2011
Posts: 7,321
Likes: 683, Points: 123, Legacy Rep: 300
Location: Spain

### TANSLSenior Member

It is not the type of stiffener as such but the high value of the web height / thickness ratio that can promote buckling.
The same can happen in a normal top hat if that ratio is high.

12. Joined: May 2020
Posts: 30
Likes: 0, Points: 6
Location: Brazil

### RoniJunior Member

There are buckling under shear criteria in the rules, they should cover that right?

13. Joined: Sep 2011
Posts: 7,321
Likes: 683, Points: 123, Legacy Rep: 300
Location: Spain

### TANSLSenior Member

14. Joined: Jul 2003
Posts: 3,062
Likes: 349, Points: 93, Legacy Rep: 1306
Location: Thailand

### AlikSenior Member

If You look at DNVGL 0342 standard, they have conversion method for inclined stiffeners. We did this for aluminium designs.

15. Joined: Mar 2021
Posts: 10
Likes: 0, Points: 1
Location: France

### ScarfJunior Member

For your question about effective shear area, the reason GL may be telling you to use height x thickness might be to remind you not to include the area of flange in your shear area.

Some Rules have limiting web depth to web thickness ratios to comply with, which tries to ensure web stability against buckling. For deep webs tripping brackets can also be provided to prevent the girder twisting under load.

Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.