Environmental Engineering Reference
In-Depth Information
disadvantages of this method are the cost of the anchors and the need to transport
them to the site.
The installation of each guy anchor and lifting/lowering station anchor should
adhere to the manufacturer's instructions. The lifting/lowering station anchor, which is
normally connected to a winch and pulley system, warrants special attention because it
must carry the entire tower load. The greatest load occurs when the tower is suspended
just above the ground. This moment provides a good opportunity to evaluate the
performance of the chosen anchors. If the anchors do not seem to be adequate for the
soil conditions, an alternative anchoring method should be identified and tested before
the tower is lifted into place. All personnel should be clear of the potential fall zone
when the tower is raised.
Under proper tension, the guy wires keep the tower vertical and minimize sway.
Inadequate or uneven tension can cause towers to bend or fall. The manufacturer's
recommendations for guy wire tension should be followed. The installation team
leader should ensure that all guy wire tension adjustments are made smoothly and in
a coordinated fashion. It is also advisable to clearly mark the lower guy wires with
reflective, high visibility material (such as brightly colored plastic guy sleeves) to alert
pedestrians and vehicle operators. This marking should conform with state and local
regulations. If large animals graze or live near the site, a fence may be necessary to
protect the guy stations and tower.
5.6.2 New Lattice Towers
New lattice towers are often employed when a very tall tower is required or when
there is a preference for manufacturing the towers locally. There are two basic types
of lattice towers: guyed and self-supporting. Both versions are usually made of fixed-
length sections connected end to end. The sections may be assembled with the tower
lying flat on the ground and the tower picked up as a unit and set in place with a
crane, or they may be stacked in place using a winch and jib pole system. The tower
sections may all look the same, but it is important that they be installed in the correct
sequence (the sections are often numbered for this purpose).
On a guyed tower, cables are attached at several heights and in at least three
directions to stabilize the structure. A self-supporting tower is wider near the base to
support the structure above it. Both types of tower require a solid base, usually on
a concrete foundation. The guyed tower requires anchor stations located at approxi-
mately 80% of the tower's height from its base. The self-supporting type usually has
three legs with a solid footing, such as a concrete pier, under each; typically, each
side of its footprint is about 10% of the tower's height.
5.6.3 Existing Towers
Existing towers such as communications towers can offer several challenges. They
come in a range of sizes and lattice designs, with the result that the sensor mounting
hardware must often be custom designed and fabricated. The design needs must be
determined during the initial site investigation; this is not a day-of-installation task.
Search WWH ::
Custom Search