Environmental Engineering Reference
In-Depth Information
4.2 Structural model for tower shaft
A structural model must be devised for the structural calculations. It is easy to see that
the primary structure comprises the tower and the foundation, whereas mast extension,
antenna platforms and plant floor are secondary structures. The latter items must be
analysed separately and their support reactions applied to the primary structure.
The structural analysis of the primary structure at the ultimate limit state requires a
numerical model that can be used to ascertain both the geometrical non-linearity (second-
order theory) and the physical non-linearity of the material laws (see Section 3.1).
Figure 4.1 shows the elements of the structural model:
1)
1. Idealisation as a bar structure with nodes at designated levels or regular intervals
(a
1
1
to 2
1
)
2. Bar elements with an annular cross-section that varies linearly (see Section 3.3.3)
3. Rotational springs for the elastic support on the subsoil
Fig. 4.1 Structural model
4.2.1 Rotation of the foundation
A permanent rotation of the foundation independent of the loading or dependent on the
permanent loading is specified as an imperfection. Such non-uniform subsoil defor-
mations must be considered in the case of cohesive soils in particular and are generally
specified by a soil mechanics specialist (see also Section 4.7.1). A brief rotation of the
foundation
w
(essentially due to the wind load) is based on a quasi-elastic subsoil
deformation and calculated as follows [51] (Figure 4.2, see also [52]):
M
found
c
s
w ΒΌ
I
found
1)
See Beton-Kalender 2006 [8].
