Design of stiffening ringsDesign of stiffening rings

Prof. Ch. BaniotopoulosProf. Ch. Baniotopoulos

I. Lavassas, G. Nikolaidis, P.ZervasI. Lavassas, G. Nikolaidis, P.Zervas

Institute of Steel StructuresInstitute of Steel StructuresAristotle Univ. of Thessaloniki, GreeceAristotle Univ. of Thessaloniki, Greece

Typical stiffening ring arrangementTypical 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)

Effects of ring stiffeners on Von mises stress Effects of ring stiffeners on Von mises stress

Left (stiffened): max σ vm=266 Mpa

Right (unstiffened) max σvm=300 Mpa

Effects of ring stiffening rings on meridional stress 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.

Effects of stiffening rings on circumferencial shell stresses 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

Stresses on stiffening rings & flangesStresses on stiffening rings & flanges

Left (stiffened): max σ vm=115 Mpa

Right (unstiffened) max σvm=180 Mpa

Stress distribution over a stiffening ringStress distribution over a stiffening ring

Effect of stiffeners to the shell buckling behaviourEffect of stiffeners to the shell buckling behaviour

Buckling mode shapes on a stiffened shell remain within one stiffened region

Use of stiffening ringsUse 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

Code provisionsCode provisions

Code provisionsCode provisions

Code provisionsCode provisions

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Code provisionsCode provisions