Editing Hyatt Regency walkway collapse (section)

==Investigation==
[[File:HRWalkway.svg|thumb|The original design vis-à-vis the final construction of the fourth-floor walkway support system. The revised design doubled the force on the nut, and hence on the welded joint of the beams which split.]]
[[File:Hyatt Regency collapse support.PNG|thumb|A cross-section of the fourth-floor support beam that fell, together with the second-floor support rod passing through its left and right halves vertically]]

''[[The Kansas City Star]]'' hired architectural engineer Wayne G. Lischka<ref name="20 years later"/><ref>{{Cite web| title=History & Education | url=http://lischka.com/Top5.html | url-status=dead | archive-url=https://web.archive.org/web/20050207031122/http://lischka.com/Top5.html | archive-date=February 7, 2005 | access-date=April 30, 2019}}</ref> and national engineering firm Simpson, Gumpertz, and Heger Inc. to investigate the collapse, and Lischka discovered a change to the original design of the walkways.<ref name="Reverberating"/> Within days, a laboratory at [[Lehigh University]] began testing box beams on behalf of the steel fabrication source.<ref name="20 years later"/> The Missouri licensing board, the state attorney general and [[Jackson County, Missouri|Jackson County]] investigated the collapse over the following years.<ref name="Reverberating">{{cite news | title=Collapse of Hotel's 'Skywalks' in 1981 is still Reverberating; in Kansas City | first=Paul J. | last=Haskins | date=March 29, 1983 | newspaper=[[The New York Times]] | url=https://www.nytimes.com/1983/03/29/us/collapse-of-hotel-s-skywalks-in-1981-is-still-reverberating-in-kansas-city.html | access-date=May 4, 2020 | archive-date=August 27, 2020 | archive-url=https://web.archive.org/web/20200827233017/https://www.nytimes.com/1983/03/29/us/collapse-of-hotel-s-skywalks-in-1981-is-still-reverberating-in-kansas-city.html | url-status=live }}</ref> Edward Pfrang, lead investigator for the [[National Bureau of Standards]], characterized the neglectful corporate culture surrounding the entire Hyatt construction project as "everyone wanting to walk away from responsibility".<ref name="20 years later"/> The NBS's final report cited structural overload resulting from design flaws where "the walkways had only minimal capacity to resist their own weight".<ref name=nbs/>{{rp|6}} Pfrang concluded they would have failed with one-third of the occupants' weight.<ref name="ap"/>

Investigators found that the collapse was the result of changes to the design of the walkway's steel [[tie rod|hanger rod]]s. The two walkways were suspended from a set of {{convert|1.25|in|mm|adj=mid|-diameter}} steel hanger rods,<ref name=Baura>{{cite book |last=Baura |first=Gail |title=Engineering ethics: an industrial perspective |publisher=Academic Press |isbn=978-0-12-088531-2 |year=2006 |page=55 |url=https://books.google.com/books?id=543gDMmaaZQC&q=hyatt+regency+hotel+Kansas+City&pg=PA55 |access-date=2020-10-23 |archive-date=2021-04-17 |archive-url=https://web.archive.org/web/20210417172042/https://books.google.com/books?id=543gDMmaaZQC&q=hyatt+regency+hotel+Kansas+City&pg=PA55 |url-status=live }}</ref> 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 the steel rods retained by nuts. The cross-beams were [[box girder]]s made from {{convert|8|in|mm|adj=mid|-wide}} 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 walkway to the ceiling, passing through the beams of the fourth-floor walkway, with a nut at the middle of each tie rod tightened up to the bottom of the fourth-floor walkway, and a nut at the bottom of each tie rod tightened up to the bottom of the second-floor walkway. Even this original design supported only 60% of the minimum load required by Kansas City building codes.<ref name="ua">{{cite web| title=Hyatt Regency Walkway Collapse| publisher=School of Engineering, University of Alabama| url = http://www.eng.uab.edu/cee/faculty/ndelatte/case_studies_project/Hyatt%20Regency/hyatt.htm#Causes|archive-url=https://web.archive.org/web/20070814044511/http://www.eng.uab.edu/cee/faculty/ndelatte/case_studies_project/Hyatt%20Regency/hyatt.htm|archive-date=August 14, 2007|access-date=January 29, 2017|url-status=dead}}</ref>

Havens Steel Company had manufactured the rods, and the company objected that the whole rod below the fourth floor would have to be threaded in order to screw on the nuts to hold the fourth-floor walkway in place. These threads would be subject to damage as the fourth-floor structure was hoisted into place. Havens Steel proposed that two separate and offset sets of rods be used: the first set suspending the fourth-floor walkway from the ceiling, and the second set suspending the second-floor walkway from the fourth-floor walkway.<ref name="whitbeck">{{cite book| last=Whitbeck| first=Caroline| year=1998| title=Ethics in Engineering Practice and Research| publisher=Cambridge University Press| location=New York| isbn=0-521-47944-4| page=116| url=https://books.google.com/books?id=pp3OIzJFB5QC&pg=PA115| access-date=2016-10-11| archive-date=2021-04-17| archive-url=https://web.archive.org/web/20210417183119/https://books.google.com/books?id=pp3OIzJFB5QC&pg=PA115| url-status=live}}</ref>

This design change would be 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 supported both the fourth- and second-floor walkways, but were strong enough only for 30% of that load.<ref name="ua"/>

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.<ref name="engineering">{{cite web| publisher=Engineering.com| access-date=June 1, 2006| url=http://www.engineering.com/Library/ArticlesPage/tabid/85/articleType/ArticleView/articleId/175/Walkway-Collapse.aspx| title=Hyatt Regency Walkway Collapse| date=October 24, 2006| archive-date=April 3, 2019| archive-url=https://web.archive.org/web/20190403123942/https://www.engineering.com/Library/ArticlesPage/tabid/85/articleType/ArticleView/articleId/175/Walkway-Collapse.aspx| url-status=live}}</ref> During the failure, the box beams split along the weld and the nut supporting them slipped through the resulting gap, which was consistent with reports that the upper walkway at first fell several inches, after which the nut was held only by the upper side of the box beams; then the upper side of the box beams failed as well, allowing the entire walkway to fall in a [[cascading failure]].<ref>NIST, p. 244</ref> A court order was required to retrieve the skywalk pieces from storage for examination.<ref name="Surviving the Hyatt">{{cite news | title=From the archives: Surviving the Hyatt skywalk disaster | first=Kevin | last=Murphy | date=July 17, 2014 | newspaper=[[The Kansas City Star]] | url=https://www.kansascity.com/news/local/article748398.html | access-date=May 4, 2020 | archive-date=August 18, 2020 | archive-url=https://web.archive.org/web/20200818023400/https://www.kansascity.com/news/local/article748398.html | url-status=live }}</ref>

Investigators concluded that the underlying problem was a lack of proper communication between Jack D. Gillum and Associates and Havens Steel. In particular, the drawings prepared by Gillum and Associates were only preliminary sketches, but Havens Steel interpreted them as finalized drawings. Gillum and Associates failed to review the initial design thoroughly, and engineer Daniel M. Duncan accepted Havens Steel's proposed plan via a phone call without performing necessary calculations or viewing sketches that would have revealed its serious intrinsic flaws—in particular, doubling the load on the fourth-floor beams.<ref name="ua"/> Reports and court testimony cited a feedback loop of architects' unverified assumptions, each having believed that someone else had performed calculations and checked reinforcements but without any actual root in documentation or review channels. Onsite workers had neglected to report noticing beams bending,<ref name="20 years later"/> and instead rerouted their heavy wheelbarrows around the unsteady walkways.<ref name="petroski"/>{{rp|103}}

Jack D. Gillum would later reflect that the design flaw was so obvious that "any first-year engineering student could figure it out," if only it had been checked.<ref name="20 years later"/>