1. Stress distribution around door-opening Prof. Ch. Baniotopoulos I. Lavassas, G. Nikolaidis, P.Zervas Institute of Steel Structures Aristotle Univ. of Thessaloniki, Greece

2. Stress distribution around door opening Main objectives to check: a)Stress distribution around the door opening b)Shell buckling at door position Linear static analysis has been performed in all cases Wind load direction x+ (producing maximum compressive stresses to the door position) Ideal stress distribution around door opening

3. Buckling analysis – no ring at all Buckling analysis a)No stiffening at all causes 1 st to 7 th buckling modes to appear in door position b)When stiffening the door by any type (thick ring, comb type stiffeners), no one of the first 10 buckling modes stands on the door.

4. No stiffeners – Vm stress distribution Max σ vm ~= 300 Mpa for the tower (excluding door position) In this case: Max σ vm =565 Mpa >> f y around the opening

5. A: Stiffening with a rigid ring (d=70 mm) around the door (existing case) Max σ vm ~= 300 Mpa for the tower (excluding door position) In this case: Max σ vm =335 Mpa around the opening First 10 eigenmodes appear to the upper part of the shell

6. Max σ vm ~= 300 Mpa for the tower (excluding door position) In this case: Max σ vm =320 Mpa around the opening Max σvm =450 to the ring >> f y  needs redesign First 10 eigenmodes appear to the upper part of the shell (identical to A:) B: Stiffening with a weak ring (d=30 mm) around the door and additional stiffeners of comb type

7. Even with presence of stiffeners, ring needs to be at least 60 mm thick Max σ vm ~= 300 Mpa for the tower (excluding door position) In this case: Max σ vm =320 Mpa around the opening Max σ vm =337 to the ring First 10 eigenmodes appear to the upper part of the shell (identical A: & B:) Stress state is almost identical to A: C: Stiffening with a ring (d=60 mm) around the door and additional stiffeners of comb type

8. Door stiffening comparison on another 45 m high 1 MW turbine tower a) Weak ring + comb type stiffeners + vertical stiffeners : Max σ vm ~= 311 Mpa b) Weak ring + comb type stiffeners : Max σ vm ~= 345 Mpa c) Only one rigid ring: Max σ vm =335 Mpa around the opening