aristotle university of thessaloniki (auth) institute of steel structures prof. c.c baniotopoulos...
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Aristotle University of Thessaloniki (AUTH)Institute of Steel Structures
Prof. C.C Baniotopoulos
Iakovos Lavasas Civil Engineer
Padelis Zervas Dr. Civil Enginner
George Nikolaidis Civil Engineer
Prestressed anchors• Finite Element modelling
•Foundation is modeled using brick elements•Anchors are modeled as non-linear tendon elements between the washer plates•Unilateral contact conditions between the washer plates and the pedestal
Prestressed anchors
• Prestress force is selected in order to eliminate anchor tensile force variation under operating wind loads
• Special concrete reinforcement is needed to carry the splitting forces on the concrete pedestal
Seismic hazard
• Mass distribution
– Concentrated on the top of the
tower with eccentricity
– Distributed over the tower
height
• Types of analysis– Eigenvalue analysis – Rensponse spectrum analysis
• Eigenvalue analysis is also
significant for the fatigue
design
Seismic hazard
• X,Y rotation spectra must be
considered together with
relevant translation spectra
(EC8-3 Annex A).
• Soil-structure interaction must
be taken into account in
eigenvalue analysis
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Period (Τ)
a (
T)
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Period (Τ)
a (
T)
Seismic hazard
• Usually seismic loads are smaller than
the extreme wind loads
• This is not obvious when constructing in a
seismic hazardous area.
• A simplified linear model can also give
satisfactory results on eigenvalue
analysis but not on seismic tower design
mi
0
Ring stiffeners
Ring stiffeners are placed to reduce the local buckling of the shell
Local buckling is produced by
Meridional compressive stresses Lower part of the tower
Circumferencial compressive stresses All over the tower height
According to EC3-1-6 buckling design, ring stiffeners are dividing the
tower into sections
Local buckling is taking place in every section
Ring stiffeners
Ring stiffener disturbance along the tower is significant for the optimization of the design
Stiffeners should be placed in order to equate (as possible) the total design ratios for every part of the tower
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De
sig
n r
atio
Tower parts between stiffeners
Door stiffeners
Stress concentration around the door opening
Scope:
• Smooth the stress concentration around the door opening
• Reduce local buckling