Three days after the disaster, Wayne G. Lischka,[16] an architectural engineer hired by The Kansas City Star newspaper, discovered a significant change of the original design of the walkways. Reportage of the event later earned the Star and its associated publication the Kansas City Times a Pulitzer Prize for local news reporting in 1982.[17] Radio station KJLA would later earn a National Associated Press award for its reporting on the night of the disaster.
The two walkways were suspended from a set of 1.25 in (32 mm) diameter[18] steel tie rods, with the second floor walkway hanging directly under the fourth floor walkway. The fourth floor walkway platform was supported on three cross-beams suspended by steel rods retained by nuts. The cross-beams were box girders made from C-channel strips welded together lengthwise, with a hollow space between them. The original design by Jack D. Gillum and Associates specified three pairs of rods running from the second floor to the ceiling. Investigators determined eventually that this design supported only 60 percent of the minimum load required by Kansas City building codes.[19]
Havens Steel Company, the contractor responsible for manufacturing the rods, objected to the original plan of Jack D. Gillum and Associates, since it required the whole of the rod below the fourth floor to be screw threaded in order to screw on the nuts to hold the fourth floor walkway in place. These threads would probably have been damaged and rendered unusable as the structure for the fourth floor was hoisted into position with the rods in place. Havens therefore proposed an alternate plan in which two separate sets of tie rods would be used: one connecting the fourth floor walkway to the ceiling, and the other connecting the second floor walkway to the fourth floor walkway.[20]
This design change would prove fatal. In the original design, the beams of the fourth floor walkway had to support only the weight of the fourth floor walkway, with the weight of the second floor walkway supported completely by the rods. In the revised design, however, the fourth floor beams were required to support both the fourth floor walkway and the second floor walkway hanging from it. With the load on the fourth-floor beams doubled, Havens' proposed design could bear only 30 percent of the mandated minimum load (as opposed to 60 percent for the original design).
The serious flaws of the revised design were compounded by the fact that both designs placed the bolts directly through a welded joint connecting two C-channels, the weakest structural point in the box beams. Photographs of the wreckage show excessive deformations of the cross-section.[21] During the failure, the box beams split along the weld and the nut supporting them slipped through the resulting gap between the two C-channels which had been welded together.
Investigators concluded that the basic problem was a lack of proper communication between Jack D. Gillum and Associates and Havens Steel. In particular, the drawings prepared by Jack D. Gillum and Associates were only preliminary sketches but were interpreted by Havens as finalized drawings. Jack D. Gillum and Associates failed to review the initial design thoroughly, and accepted Havens' proposed plan without performing basic calculations that would have revealed its serious intrinsic flaws — in particular, the doubling of the load on the fourth-floor beams.
http://en.wikipedia.org/wiki/Hyatt_Regency_walkway_collapse
