14 THE DISTRIBUTOR’S LINK Laurence Claus Laurence Claus is the President of NNi Training and Consulting, Inc. He has 25 years of experience with a medium sized automotive fastener manufacturer, holding positions including Vice President of Engineering, General Manager, Director of Quality, Director of New Business Development and Applications Engineer. In 2012 he formed NNi offering technical and business training courses as well as technical consulting, expert witness and consultation work. He can be reached at 847-867-7363 or by email: Lclaus@NNiTraining.com. You can learn more about NNi at www.NNiTraining.com. WHY FASTENERS FAIL PART 2 - OVERLOAD, FATIGUE AND CREEP On December 7, 1982 riggers were lifting the final section of the planned Senior Road Radio Transmission Tower into place. The Senior Road Tower was a 1975 foot tall guy-wired radio mast in Missouri City, Texas. It was the planned new transmitting site for five FM radio stations. At 1975 feet it would be about 100 feet short of being the tallest structure in the world at the time. Construction of the tower was done in stages. Sections would arrive on flatbed trucks, be lifted off, hoisted into place and connected one after the other. All had gone without difficulty until they reached the final section. Unlike the other sections, which were basically just structural framework, the final section had many dishes and antenna components attached to its side. This posed a problem because, although the fabricators had wisely attached lifting eyes to each section to aid removal from a truck and in hoisting, the dishes were located so that once the section began to transition from the horizontal position it was lifted off the truck into a vertical position to hoist it in-place, the hoisting wires would contact and damage the dishes. Since this was not an acceptable alternative, the riggers requested that the offending dishes be removed and be reassembled after the last section had been connected. Fearing that reassembly might not restore the dishes to their proper positions, which could affect future signal transmission, this request was denied. Faced with this dilemma, the riggers constructed a set of “outriggers” that would extend the hoisting cable connection points outward TECHNICAL ARTICLE and away from the fragile dishes. These “outriggers” were jerry-rigged assemblies of whatever they had at their disposal and were fixed to the main structure using several run-of-the mill U-Bolts. With a solution in-hand, the riggers began hoisting the final 12,000 pound (6 ton) section. As it reached about the 1000 foot mark, one of the U-Bolts gave way causing a chain reaction failure of the other U-Bolts and “outriggers”, releasing the section to hurtle to the ground. As it fell, it contacted and severed two of the twenty-four supporting guy wires. Instead of slicing right through them, however, it initially bent the tower in that direction and sent it whipping back once the guy wire severed and released tension on the tower. This resulted in the failure of the other guy wires and sent the entire tower crashing to the ground. Tragically five riggers, three that were riding the hoisted section and two that were positioned at the top of the tower to receive the section, fell to their death. FIGURE 1: CRUMPED STRUCTURE AND GUY WIRES OF THE COLLAPSED TOWER CONTINUED ON PAGE 126
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