Stress distribution around door-openingStress distribution around door-opening

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

Stress distribution around door openingStress 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 casesWind load direction x+(producing maximum compressive stresses to the door position)

Ideal stress distribution around door opening

Buckling analysis – no ring at allBuckling analysis – no ring at all

Buckling analysis

a) No stiffening at all causes 1st to 7th 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.

No stiffeners – Vm stress distributionNo stiffeners – Vm stress distribution

Max σvm ~= 300 Mpa for the tower (excluding door position)In this case: Max σvm=565 Mpa >> fy around the opening

A: Stiffening with a rigid ring (d=70 mm) around the door (existing case)A: Stiffening with a rigid ring (d=70 mm) around the door (existing case)

Max σvm ~= 300 Mpa for the tower (excluding door position)In this case: Max σvm=335 Mpa around the opening

First 10 eigenmodes appear to the upper part of the shell

Max σvm ~= 300 Mpa for the tower (excluding door position)In this case: Max σvm=320 Mpa around the openingMax σvm =450 to the ring >> fy 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 B: Stiffening with a weak ring (d=30 mm) around the door and additional stiffeners of comb type stiffeners of comb type

Even with presence of stiffeners, ring needs to be at least 60 mm thick

Max σvm ~= 300 Mpa for the tower (excluding door position)In this case: Max σvm=320 Mpa around the openingMax σvm =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 C: Stiffening with a ring (d=60 mm) around the door and additional stiffeners of comb type stiffeners of comb type

Door stiffening comparison on another 45 m high 1 MW turbine towerDoor stiffening comparison on another 45 m high 1 MW turbine tower

a) Weak ring + comb type stiffeners + vertical stiffeners : Max σvm ~= 311 Mpa b) Weak ring + comb type stiffeners : Max σvm ~= 345 Mpac) Only one rigid ring: Max σvm=335 Mpa around the opening