Loadbearing structures and detailed design - Concrete Structures for Wind Turbines - page 184

4.10.4 Example of calculation
A statically indeterminate analysis will be carried out to determine the characteristic
values of the loads for the design of the detail in Figure 4.46.
Cross-sectional values:
The stiffness of the tubular steel segment is neglected. Therefore, only the radius is
required for the load transfer:

:

r o ¼ 2

:

Radius of tubular steel segment 10 m

The strengthening to the top of the reinforced concrete tower is idealised as a circular
ring beam as follows:

Beam radius: r R 2.25m

Beam width: b R ¼ 1.20 m

Beam depth h R 2.20m

The annular flange to the tubular steel segment can be considered as part of the circular
ring beam, but is neglected here for simplicity, likewise the reinforcement.

Cross-sectional area:
A c b R h R ¼ 1.20 2.20 ¼ 2.64 m 2

Second moment of area:
I R b R h R 3 /12 ¼ 1.20 2.20 3 /12 ¼ 1.065 m 4

The reinforced concrete tower itself is idealised as a cylindrical shell:

Shell radius: r u ¼ 2.675m
Shell thickness: t u ¼ 0.35m
Shell parameter according to [64]:

4 q

3

4 q

3

2 2

2 2 k u ¼ ð 1 m

2

Þ ð r u = t u Þ ¼ 1 0 : ð 2 : 675 = 0 : 35 Þ ¼ 3 : 601

A uniform elastic modulus is used: E c ¼ 30 000 MPa
Statically determinate primary system:
The statically indeterminate analysis is carried out for a constant unit twisting moment
(symmetrical loading: m R0 ¼þ 1 MNm/m).
Unit bending moment in circular ring beam:
M R0 ¼ m R0 r R ¼þ 1 2

:

25 ¼þ 2

:

25 MNm