Environmental Engineering Reference
In-Depth Information
Fig. 10.7 Finite element
model of 18 m tubular lattice
tower. At left, the blue (thick)
lines show the horizontal and
vertical members and the red
(thin) lines the cross-bracing.
At right is a close up of the
bottom section with the
relative magnitude of the
wind load shown by the
arrows. The wind is blowing
in the positive Z direction.
The maximum (compressive)
stress of 156 MPa occurs in
the lowest ''back'' leg. Note
that the FE model does not
include the base plates and
connection plates between
sections or the gussets.
Images from Benn Lakin
Table 10.6 Specifications of lattice tower
General specifications
h = 18 m. Tower mass, m T = 640 kg
Base distance between legs 1.975 m
Vertical and horizontal
members
Low carbon steel. F y = 255 MPa. 60.5 mm diameter pipe. Wall
thickness: 3.65 mm
Cross bracing
Low carbon steel.F y = 255 MPa Solid round bar, 12.7 mm
diameter
divided by the section area. The drag coefficient then depends on the shape of the
members, the direction of the wind, and, for circular members, whether the flow is
super- or sub-critical. This distinction relates to whether the boundary layer flow
on the member is laminar or mainly turbulent. In some standards, such as AS 3995
[ 17 ], the coefficient also depends on whether the lattice is three- or four- legged.
From the drag coefficient and extreme wind speed, the load on each section can be
determined for each orientation. None of this is difficult, but it is tedious, and can
induce the designer to rethink the use of a monopole!
The tower in Fig. 10.7 was designed to use the same materials and have the
same base dimensions as towers made by Kijito Windpower for water pumping
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