Windmilling The Anatomy Of A Tower Catastrophe
By Robert F. Gonsett ©1999 Communications General Corporation
This article describes the step-by-step events that led to the tower
collapse which claimed the life of Andy Figge, a well respected rigger
and Registered Professional Civil Engineer. The article was written at
the request of several Southern California broadcast engineers who had
close ties with Andy and wanted to understand the events that cost him
his life. Hopefully, this understanding will help others avoid similar
tragedies.
Most of the technical information in this article was obtained from
Ernie Jones, a Registered Professional Mechanical and Civil Engineer.
Ernie visited the accident scene as a good neighbor and pieced together
the events from interviews and physical evidence. Additional data were
provided by Ralph Young, president of Empire Crane Service, and Hundley
Batts, one of the owners of the broadcast station where the tragedy
occurred. A small amount of non-technical information was gleaned from a
Huntsville Times article of February 12, 1999.
Here, then, is how the tragedy appears to have unfolded:
On February 10, 1999, Andy Figge was in the process of installing a 250
foot guyed uniform cross-section tower at Radio Station WEUP(AM),
Huntsville, Alabama. He had erected the first 100' of tower and had
attached three fiberglass guy lines to the top of that tower. The
remaining 150 feet of tower was laying on the ground in a continuous
length where it had been preassembled out of 10 foot sections. The plan
was to use a crane to set the 150 footer on top of the existing 100
footer, and that would be done in two stages.
The first stage involved connecting a crane cable to the side of the 150
footer so there was about 60 feet of tower on one side of the connection
point and 90 feet on the other. The 150 foot section was successfully
lifted upright and temporarily set parallel against the existing 100
foot tower section with the bottoms of both sections essentially at
ground level. (The base of the 100 foot section was anchored to its
"point type" foundation while the bottom of the 150 footer was resting
firmly on the ground.)
Since the crane was not tall enough to lift the 150 footer into place
with the crane cable attached at the 90 foot mark, Andy reconnected the
cable to a point that was only 70 feet above ground. That left 80 feet
of tower above the connection point and caused an obviously unstable
situation where the tower could "windmill" and turn over. Andy had
anticipated that state of affairs and had already attached weights to
the bottom of the 150 foot section to prevent overturning.
In the second stage of the project, Andy was atop the 100 foot tower
section and secured to the tower with his climbing belt. He was ready
to bolt the bottom of the 150 footer to the top of the 100 footer as
soon as the crane completed the lift.
A decision was made to raise the 150 foot section, just a little, to
make sure that the added weights were sufficient to prevent windmilling.
Unfortunately, the weights were not sufficient. The bottom of the 150
foot tower section moved out horizontally at an alarming rate (the crane
cable attachment point serving as the pivot) and the bottom of the 150
footer headed directly for the studio/transmitter building.
The crane operator reportedly tried to set the load down, but could not
do so in time. Seconds later, the bottom of the 150' tower section
slammed into the underside of the roof eave. That brought the rotation
of the 70 foot portion to a halt. Of course, the 80 foot portion wanted
to keep going.
This state of affairs put tremendous strain on what we could now call
the "top" tower leg of the 150 foot section. A leg bolt broke
(calculations suggest that its ultimate strength was exceeded) so that
the 150 foot section folded in two with the 80 foot end eventually
coming to rest on one of the fiberglass guy wires that held Andy's 100
foot tower section upright. The guy line reportedly held at first, then
broke as the tower metal slid down and sheared or sliced the line.
Andy was never able to unbuckle himself and rode the 100 footer down as
it toppled onto the roof of the studio/transmitter building. He was
reportedly killed instantly. There were no other injuries or fatalities
associated with the accident.
Ralph Young, president of Empire Crane Service, commented that a safety
meeting had been held on Monday prior to the job, and that the crane
operator had attended. Andy presented himself professionally and there
was no question in anyone's mind that he had carefully thought over each
step of the job, and that he was well qualified to complete it.
Through the course of this project, the staff and management of Empire
Crane and WEUP had grown to respect and care about Andy as an
individual. They were severely shaken by the tragedy. Empire Crane had
reportedly been in business 34 years without a major injury accident.
By clearly understanding the step-by-step events that led to the
fatality, it is hoped that similar accidents will be prevented.
Read the tributes to Andy Figge >>
This article is published as part of the CGC Communicator newsletter and
may be reprinted or republished - free of charge - provided the story is
unaltered and printed in full, including this section.
Past issues of CGC Communicator newsletters may be viewed at:
http://www.bext.com/cgc/
Stories that pertain to this incident begin with CGC Newsletter #312.
|