INTRODUCTION

                                             MECHANICS AND STRUCTURES

April 27, 1978: In West Virginia, 51 construction workers fell 170 feet to their deaths as the scaffold and form work system peeled from the top of a cooling tower under construction. The lack of some required bolts connecting the scaffold to the tower and inadequately cured, insufficient strength concrete contributed to the accident. May 30, 1979: A DC-10 crashed in Chicago, killing 271 people. A 3 /8-inch diameter bolt supporting the engine pylon failed, causing the engine to break away from the wing. As it broke away, it ripped through three redundant hydraulic flight control lines. May 12, 1982: A report to Congress stated that more than 212,000 of the nation’s 525,600 highway bridges (40.5%) were structurally deficient or functionally obsolete. A structurally deficient bridge is one that has a reduced load, is closed, or must be rehabilitated immediately. A functionally obsolete bridge can no longer safely serve its current traffic load because of lane width, load carrying capacity, clearance, or approach alignment. June, 1979: The driver of an off-highway dump truck was crushed to death in the cab when the loaded truck’s chassis collapsed. Although the exact cause is not known, some speculated that metal fatigue caused the collapse. August, 1989: It was found that bolts that did not meet standards for strength and other properties were marketed for use in aircraft, trucks, and many other applications without the knowledge of the using companies. The bolts had been certified to meet standards, when in fact, they were manufactured and imported as inferior. Their lower production cost provided a price advantage to their marketing companies. The Federal government became heavily involved in investigating the distribution of inferior bolts throughout the United States. Some companies that imported and sold inferior bolts were criminally charged. The problem of knowing which bolts are inferior and where they are in use is virtually impossible to solve. 1995: As a worker stepped on a plastic skylight cover to gain access to an air conditioning unit on a plant roof, the plastic cover failed and the worker fell to the concrete floor 20 feet below the skylight. After being exposed to ultraviolet light for many years, the plastic skylight cover had lost much of its strength. 1998 and 1999: After six deaths and many more injuries to auto racing spectators at racing events, designers re-evaluated standards for separating speeding vehicles and crash debris from fans.

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