1. Design of stiffening rings. Prof. Ch. Baniotopoulos I. Lavassas, G
Design of stiffening rings Prof. Ch. Baniotopoulos I. Lavassas, G. Nikolaidis, P.Zervas Institute of Steel Structures Aristotle Univ. of Thessaloniki, Greece

2. Typical stiffening ring arrangement
When used, stiffening rings are placed over the height of the cylinder, separating it to regions
Distances between rings are a question of
buckling limit state design (LS3)

3. Effects of ring stiffeners on Von mises stress
Left (stiffened): max σ vm=266 Mpa
Right (unstiffened) max σvm=300 Mpa

4. Effects of ring stiffening rings on meridional stress
Left (stiffened): max σz=219 Mpa
Right (unstiffened) max σz=240 Mpa
The existence of rings should have no effect to the meridional stress. The difference appears
around door position.

5. Effects of stiffening rings on circumferencial shell stresses
Left (stiffened): max σθ=63 Mpa
Circumferencial stress is distributed over the rings
Stiffeners are forcing the cylinder sections to remain circular
Right (unstiffened) max σθ=109 Mpa
Circumferencial stress is concentrated to the flange positions where the ovalling deformed shape of the cylinder is forced to circular due to the stiffness of the flange

6. Stresses on stiffening rings & flanges
Left (stiffened): max σ vm=115 Mpa
Right (unstiffened) max σvm=180 Mpa

7. Stress distribution over a stiffening ring

8. Effect of stiffeners to the shell buckling behaviour
Buckling mode shapes on a stiffened shell remain within one stiffened region

9. Use of stiffening rings
Advantage:
- Use of stiffening rings may reduce shell thicknesses mainly to the upper parts of the tower where local buckling is the main design issue
Disadvantage:
Although the cost of the materials is less in a stiffened tower, the cost of the work is more
The total cost of the tower may be bigger for the stiffened tower

10. Code provisions‏

11. Code provisions‏

12. Code provisions

13. Code provisions

14. Code provisions