Towers Falling Free Online Book

[Rosita Westhouse]

In1982, TV Antenna Tower collapsed killing several people. The catastrophe was captured on film, and the film record aided the investigation in ascertaining the cause of the incident. The case illustrates how a short sighted concern to avoid legal liability may undermine an engineer's ability to fulfill his or her responsibility, to ensure safety on the construction site, and lead to negligence

The case is particularly well suited for integration into statics, construction engineering and structures courses. Detailed diagrams of the antenna design and photographs of the collapsed tower sections are included in the PDF version of the case.

Total collapse during installation of a 6-ton FM antenna being placed on a new 1800 ft. tower. 5 technicians killed, 3 on the hoist and 2 on the tower. It was determined that insufficient sized bolts on a makeshift lifting lug extension failed. The falling debris severed one of the tower's guy wires, causing the tower to collapse.

The following case is based on an actual incident. However, individual actors and company names have been changed due to possible pending litigation. In addition, although conversations and memorandums used are based on evidence surrounding the case, they are hypothetical in nature, and are used to illustrate important issues rather than to attempt an actual reenactment of what "really" happened.

In 1982, a television station video crew was filming the raising of their new television tower. The antenna was designed and manufactured by Antenna Engineering, Inc., a moderately-sized local firm. Riggers, Inc., a small local firm, was contracted to raise and assemble the antenna. During the initial design, Antenna Engineering submitted antenna plans to Riggers for their approval. Riggers approved the plans which provided for placement of the antenna hoisting lugs. These lugs provided attachment points for lifting cables which would be used for removing the antenna sections from the delivery truck, and for hoisting the antenna into the air for final assembly on a 1000 foot tower. A crew of riggers who had constructed such towers for many years was on-site. The crew used a vertically-climbing crane mounted on the already constructed portion of the tower to lift each new section of the tower, and finally, the two-section antenna onto the top of the tower. The design called for a three-legged tower, and as each new section was lifted, it was positioned and bolted onto the previous tower sections, one piece at a time. The tower legs were solid steel bars with 8 inch diameters. The tower sections weighed approximately 10,000 pounds and were each 40 feet long. They were raised without incident to a height of about 1000 feet.

The two final antenna sections arrived at the site and assembly proceeded as planned, until the last antenna section was ready to be hoisted into position. This section was different from the other sections of the antenna because it had microwave baskets attached to the sides of the antenna. The placement of the hoisting lugs allowed the antenna to be lifted horizontally off of the delivery truck, but the baskets interfered with the lifting cables when the antenna was rotated to a vertical position. A make-shift extension to the lifting lug had to be fashioned by the riggers to permit the last section's vertical hoisting. Unfortunately, on the day of videotaping during the hoisting of this last section, something went wrong, and while the antenna was being hoisted, the bolts on the make-shift lifting lug extension failed. The result was a tragedy. Several riggers fell 1000 feet to their death.

The video camera caught this catastrophe on film, and through its footage, investigators were able to discover where the failure initiated, and why the accident occurred. The case of the antenna tower collapse raises serious questions about the design engineer's social responsibility to ensure safety on the construction site, and poses additional questions about product liability issues in engineering and ethics.

Ethical issues raised by the case involve social responsibility versus legal liability, engineering responsibility for failed innovation, problems associated with design implementation, and liability and negligence issues. While valuable for all engineering students, the case is particularly well suited for statics, construction engineering and structures courses.

Instructors preparing to lead class discussion on this case will find particularly relevant essays #4, "Engineering Design: Literature on Social Responsibility Versus Legal Liability," and #5, "Negligence, Risk, and the Professional Debate over Responsibility for Design," both appended at the end of the cases in this report. In addition, essays #1 through #3 appended at the end of the case listings in this report will have relevant background information for the instructor preparing to lead classroom discussion. Their titles are respectively: "Ethics and Professionalism in Engineering: Why the Interest in Engineering Ethics?;" "Basic Concepts and Methods in Ethics;" and "Moral Concepts and Theories."

William (Bill) Harris -- President. Harris recommended to Jordan that Antenna Engineering, Inc. not get involved with Riggers problems regarding lifting the antenna tower, due to legal liability issues.

Harry Jordan -- Head of the Engineering Division. Jordan told Riggers that they could not authorize removing the microwave baskets, yet he also told Riggers that the engineering firm signed off responsibility once Riggers accepted their design plans.

Randall Porter -- Vice President. Made initial call to Antenna Engineering, Inc., detailing the problems Riggers was having lifting the top antenna section with the microwave baskets on it.

The Problem: Riggers, Inc. could not hoist the last antenna section using the lifting lugs Antenna Engineering provided due to interference with microwave baskets. Antenna Engineering refused permission for Riggers to remove the basket and reassemble after hoisting.

Assuming that the angle that the tower hangs is relatively small, which it was, and that the bolts were about 1 foot apart, and that the supporting channel was about 6 feet long, the load in the bolts is actually a combination of direct shear (as found previously, plus the load due to the moment caused by the length of the channel. Thus:

The corresponding shear stress on each bolt is thus: Stress = (7*Antenna Weight)/Area of bolt or, in other words, the stress (for these assumed numbers) in the bolts is seven times what the Riggers thought it would be.

5) Should Antenna Engineering have recommended another consulting engineer to assist Riggers? Should they have notified their professional society? Was it ethical for the engineers at Antenna to wash their hands of the project without attempting to find a resolution for Riggers? What other measures could they have taken to assist Riggers without becoming legally entangled?

The following case is based on the actual incident. However, individual actors and company names have been changed due to possible pending litigation. In addition, conversations and memorandums used are based on evidence surrounding the case; however, they are hypothetical in nature, and used to illustrate important issues involved in the case rather than to attempt an actual reenactment of what "really" transpired.

During the construction of a major TV tower/antenna, a television station video crew was filming the construction. Their station was to use the antenna to extend their station's range, and they would film the operations daily for use in their news broadcasts. The antenna was designed by Antenna Engineering, Inc. Riggers, Inc. (a small local firm) was contracted to raise and assemble the antenna. During the initial design, Antenna Engineering submitted plans to Riggers for their approval. Riggers approved the plans which provided for placement of several hoisting lugs. These lugs provided attachment points for lifting cables which would be used for removing the antenna sections from the delivery truck, and for hoisting the antenna sections into the air for assembly. A crew of seven riggers who had constructed such towers for many years was employed. The crew used a vertical climbing crane, mounted on the already-constructed portion of the tower to lift each section of the antenna into the air. The design called for a three-legged tower. Each section was lifted and strapped onto the tower, one piece at a time. The anchor points for these sections were very accurately set.

The antenna sections arrived at the site and assembly proceeded as planned, until the last antenna section was ready to be hoisted into position. This section was different from the other sections of the antenna, because it had microwave baskets attached to the side of the antenna. The placement of the hoisting lugs allowed the antenna to be lifted horizontally off of the delivery truck, but the baskets interfered with the lifting cables when the antenna was rotated to a vertical position for bolting onto the previous section. Riggers called Antenna requesting redesign assistance to fix the problem, but Antenna declined. Riggers then requested permission to remove the microwave baskets to clear the lifting cables, which was refused. A make-shift extension to the lifting lug had to be fashioned by the riggers to permit the last section's vertical hoisting. When the last section was hoisted, something went wrong. The bolts on the make-shift lifting lug extension failed while the antenna was being hoisted. The result was a tragedy. Several riggers fell 1000 feet to their death.

The video camera caught this catastrophe on film, and through its footage, investigators were able to discover where the antenna debris landed and why the accident occurred. The case of the antenna tower collapse raises serious questions about the design engineer's responsibility to ensure safety on the construction site and poses additional questions about product liability issues in engineering ethics.

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