Environmental Engineering Reference
In-Depth Information
Fig. 4.45 Modi
cation factor l
c2
(N,
a
) for effective minimum stress S
cd,min
ΒΌ0.8
4.10 Design of construction nodes
Special attention must be paid to the construction nodes during the design. Those
include the connections of attached components, for example annular platforms on
telecommunications towers. Such items can either be connected directly to the tower
shaft or (in the case of large internal forces) via a strong circular ring beam. Examples
can be found in [8].
Adapter details are necessary in hybrid towers for wind turbines at the transition from
the prestressed concrete tower to the tubular steel segment (Figure 4.46).
4.10.1 Loads on nodes
The abrupt change in the tower diameter leads to high change-of-direction forces (see
Figure 4.47). These loads can only be accommodated by circular ring beams with a
depth at least equal to their width, preferably 20 to 30% greater! Expressed in more
graphical terms: with a square cross-section, the change-of-direction forces to be
accommodated by conventional radial reinforcement are equal to the sum of the
vertical compression in the shaft wall, the concrete and the reinforcing steel.
4.10.2 Composition of forces at the ultimate limit state
a) Prestressed concrete tower (bar with annular cross-section):
Design values
:
N
Ed
;
M
Ed
;
V
Ed
The characteristic values of the internal forces (N
Gk
,M
Gk
;N
P, k
;N
QN,k
,M
QN,k
;V
QW,k
,
M
QW,k
) result from the equilibrium conditions for the deformed structure with the
characteristic values of the actions (G
k
,Q
N,k
,Q
W, k
).
