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Tower
Reinforcing
Tower
Reinforcing Can Save Millions of Dollars
Consider
the value of your time, resources and the likelyhood you will experience
months of hassle with the FCC and FAA.
• Steel
prices and availability have skyrocketed recently
• Communities
are fighting the construction of new towers of any kind
• Getting
approvals through the FCC and the FAA are taking longer than ever before
• New
tower construction can easily take more than a year, while reinforcing
can usually be completed in a matter of a few months
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Tower
Reinforcing - Ask the Real Professionals
This vintage 1948 Blaw-Knox tower was brought up to TIA/EIA-222
rev F after three independent engineers told the owner it could
not be upgraded. One of the reports came from engineers who worked
for a tower fabricator - their primary interest was in selling
a new tower. The other two reports came from well known structural
engineers who do not specialize in reinforcement.
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Tower
reinforcement is a specialized area of structural engineering.
It requires intuition, logic and most of all, patience. In other
words, thinking outside the box. It is not hard to determine where
a tower's weak points are but the key is to have the patience
and expertise to develop a reinforcement plan that does not create
more problems than it cures.
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When
larger members or redundant members are added to reinforce a weak
area of a tower at a midpoint, they can create additional wind
load or weight to the tower. That can often have an adverse affect
on another area below, or in some cases even above the point of
reinforcement. For instance, changing out round tension rods in
favor of angles can more than double the wind loading in that
area. Increasing guy wire size can add considerable weight to
already stressed legs and internal members below. The list goes
on and on.
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Research
and testing is the key to any reinforcement program. BTTi has
committed major time and resources on testing various methods
of reinforcement. Utilizing tower member models and working
closely with a major university test lab we thoroughly test
our concepts and prove our theories with hard data. Recent testing
using clamp-on leg reinforcement yielded far greater strength
than we had previously experienced. While unreinforced leg samples
failed at an average of 30.4 kN, reinforced samples held on
until 53.9 kN. That is an average of 77% increase in strength.
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For
years the tower industry has accepted welded-on reinforcement
as the conventional method for adding strength to tower legs.
This method has numerous inherent flaws. Foremost, it is extremely
time consuming. According to the Welding Institute, a half inch
weld using proper heat, rod and procedures should run at a rate
of 35 inches per hour. If this could be accomplished under the
adverse conditions of welding on a tower leg one could expect
to weld just 12 feet of angle over angle in a single 8 hour day
(remembering that you have to weld both sides of that 12 foot
piece). In the case of split pipe over round legs, the amount
of reinforcement would be half that since there are 4 edges to
be welded so you can only expect 6 linear feet in a standard 8
hour shift. In addition to time, there are the factors of unknown
material composition, fire from falling slag (to the welder, the
feedlines and the environment below) and of course the possibility
of damage to the tower from using the wrong heat, etc. BTTi uses
welding only in limited applications and under the strictest supervision.
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