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

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)

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 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 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 & flanges Left (stiffened): max σ vm=115 Mpa Right (unstiffened) max σvm=180 Mpa

Stress distribution over a stiffening ring

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

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

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