"The demolition of a section of the Cypress Viaduct still standing after the collapse in the Loma Prieta earthquake, illustrates graphically the problem of progressive collapse. A large part of the viaduct, sited to the east of San Francisco Bay, suffered catastrophic collapse of its upper deck in the earthquake, causing over 40 deaths. A section of four bays, which was supported by five bents, was left standing. A wrecking ball was swung to impact on one of the end columns in the second level, as illustrated above. After several impacts, the column in question failed; this failure was immediately followed by the collapse of the remainder of the structure. This tendency to progressive collapse must have contributed to the loss of life."
