Mothman

Many people in the West Virginia and Ohio area claim to have heard a 'Sonic Boom' around the same time, or just moments before the bridge fell. Investigators checked with the nearby military installations, and there were no aircraft capable of producing a Sonic boom in the area at the time the bridge dismembered. The theory was proven false after the researcher's investigation showed that surrounding buildings were not damaged. If a sonic boom had occurred in a residential community, the overpressure would have caused extensive damage to homes and other structures in the Point Pleasant area.(15)

Older residents claimed that the cause of the bridge collapse was "The Curse of Cornstalk." In 1774, the Battle of Point Pleasant took place between approximately 1,000 white men and 1,000 Indians. The commander of the Indian war party was Chief Cornstalk, a well-respected and intelligent Indian leader. During the battle, Cornstalk could see that defeat was imminent for his forces. He therefore let his troops make a crucial decision, either to fight to the death or surrender. The Indian warriors chose to surrender. With the surrender, Chief Cornstalk signed the Treaty of Camp Charlotte.(16) Chief Cornstalk and his son were later captured and murdered along with his son at Fort Randolph. Legend states that in his dying words Chief Cornstalk, still upset over his troops defeat, placed a curse of death and destruction upon the entire Point Pleasant area.(17) Could this be the reason for the collapse of the Silver Bridge? After thorough investigations of the bridges' collapsed structure, 'The Curse of Cornstalk' was ruled out as a contributing factor to the collapse of the Silver Bridge.

After extensive studies of the broken structure members, the cause of failure was determined. The answer was the unique eye-bar design made from the newly innovated heat treated-carbon steel. The old saying, "A chain is only as strong as its weakest link," turned out to be a fact in the failure of the Silver Bridge.(18) The heat-treated carbon steel eye-bar broke, placing undue stress on the other members of the bridge. The remaining steel frame buckled and fell due to the newly concentrated stresses.

The cause of failure was attributed to a cleavage fracture in the lower limb of eye-bar 330 at joint C13N of the north eye-bar suspension chain in the Ohio side span." The fracture was caused from a minute crack formed during the casting of the steel eye-bar. Over the years, stress corrosion and corrosion fatigue allowed the crack to grow, causing the failure of the entire structure. At the time of construction, the steel used was not known for subduing to corrosion fatigue and stress corrosion. Inspection prior to construction would not have been able to notice the miniature crack. Over the life span of the bridge, the only way to detect the fracture would have been to disassemble the eye-bar. The technology used for inspection at the time was not capable of detecting such cracks. (19)