 Architects and engineers strive for striking an innovative design. Minor adjustments in a design are common over the life of a construction project, although each amendment should be stress tested in order to keep the overall design parameters, but sometimes this is overlooked. A hotel in Kansas City would highlight the culture of building maintenance in the 1970s, that favoured looks and ease of construction above all else. The disaster would only be one of several structural failures of the era, with the 1976 Tent and Dam collapse, 1978 Hartford Civic Centre roof collapse and the 1979 Kemper Arena roof collapse just to name a few. Almost to the day after its completion, a hotel in Kansas City, Missouri experienced a structural failure causing the deaths of 114 people. It still remains the deadliest non-deliberate structural failure in American history. Today's disaster shows how something you assume to be safe can be the source of a catastrophic failure resulting in the loss of life. And as such, I'm going to rate it here 8 on the plainly difficult disaster scale. The suspended walkways are often seen in hotels, shopping centres and museums. Several of these would be a defining feature of the Hyatt Regency's lobby. The Hyatt Regency is part of the Crown Centre complex built by Hallmark Cards, adjacent to where most of Kansas City's tallest buildings are located. Construction began in May 1978 and the hotel complex consisted of a 40-storey tower, a function building and a connecting atrium area. The total rooms was 733 and on top of the main building sat a rotating restaurant. The hotel also had a 17,487 square foot ballroom and a dedicated exhibition hall. The atrium area was multi-floored and employed three suspended walkways to connect the tower to the function building on the second, third and fourth floors. The third floor walkway was independently suspended from the atrium roof trusses, whereas the fourth floor walkway was suspended from the roof framing. The second floor walkway was suspended from the fourth. The atrium measured 117 feet north-south by 145 feet east-west with a ceiling height of around 50 feet and the walkways ran in a north-south direction. The third floor walkway was the widest as it ran to the ballroom area and was intended for large quantities of people. Each walkway was constructed from four pieces made of a steel-framed box girders welded together and suspended by one and a quarter inch diameter rods at the end of each piece. Now the original design intended that the rod would be continuous through the fourth floor walkway to the second floor walkway. Under this arrangement, each box beam was separately transfer its load directly into the hanger rods and onto the atrium roof. This setup necessitated threads along the whole length of the rod. The fabricator worried that the threads would get damaged during construction and instead suggested an amendment to the design. Instead of continuous rods, two separate rods would be used, one running from the roof to the fourth floor walkway, with the next set of rods next to it down to the second floor walkway. This had an unwanted side effect and that was the transference of force leading to the fourth floor having to hold up both itself and the second floor. The weight on the roof would still be the same, but a nut at the end of the first rod would have to support two levels instead of the one original in the design. The fault was not picked up by the designers. A concrete slab was placed on top of the metal frame and formed the walkway. Tempered glass plates held in extruded aluminium gaps and the base of the walkway formed the handrails. The walkways were approximately 120 feet long and weighed approximately 64,000 pounds. Construction completed in 1980 and on the first of July, that same year, the hotel opened to paying customers. This leads us on to the 17th of July 1981. A little over a year after its opening, the hotel was hosting a tea dance to between 1200 to 2000 people in the atrium. The event started at 3pm. By 4.30pm most of the seating in the atrium area was occupied and many started to spread throughout the various levels. The busy atrium was brimming with people and because of this, many had made their way up to the walkways for a better view of the evening. By 7pm the evening was in full swing and the band returned from a break to begin to play. Around the same time, spectators on the fourth floor walkway experienced a strange and unnerving metal scraping sound. At 7.05pm the fourth floor gave way, falling onto the crowded second floor. The impact pushed both floors onto the atrium first floor below. Many bodies were buried beneath the steel, glass and concrete with many still alive. At 7.08pm the emergency call was sent out to the Kansas City Fire Department. Within minutes, Fire Department first responders arrived on the scene and requested additional help and equipment to launch a rescue effort. Nearly 20 minutes post-collapse, a forklift was requested. Before the end of the first hour, more than 100 firefighters and emergency workers were involved in the rescue operation. A total rescue operation would last 14 hours well into the afternoon of the 18th with the recovered dead bodies stored in a makeshift morgue in the exhibition hall. Any available space away from the atrium was used for triage of the wounded. Walking wounded made their way to A&E whilst more seriously injured were treated on site. One such person had their leg amputated by a doctor with the use of a chainsaw. The hotel's sprinkler system was damaged during the collapse and a real risk of flooding was feared. In the wake of the disaster, blood centres received hundreds of donations and anyone who could help did with the rescue efforts. With over 200 injured and a total of 114 dead, how could the collapse have happened in such a modern building? With a shocking disaster in a new building, investigators were faced with a failed structure and the question how. The NSB, on a national bureau of standards, began their investigation on the 28th of July, after a court order covering protective custody of the debris was given to the investigators. Initial measurements, inspections and photographs were taken of the debris and remains of the fourth and second walkways. They found something strange on the four floor box sections. The seam weld was strangely bent in a line near where the rods met the walkway, the same part that had been redesigned by the fabricators of the rods. What was also odd was that a number of the washers used at the nut of the rods of the fourth floor were either missing or severely deformed. The theory that was posited was that the stress on the cross beams of the fourth floor had split the welds on the beam seam allowing the floor to slip on top of the second. To prove the theory, the MBS conducted a number of stress tests on identically fabricated segments. The MBS found during its investigation that the constructed walkways were considerably less capable of holding up the design loads specified by the Kansas City Building Code. They also concluded that the rods of the fourth floor walkway had failed causing the total collapse, most notably at the box beam rod connections, where the design had been changed by the fabricator. It was predicted that the original design of a continuous rod was 90 kilonewtons, whereas the actual installation of the interrupted two rod arrangement was 181 kilonewtons, double the designer's spec. It was also found out that the continuous rod arrangement would have handled the loads on the walkway on the 17th of July. Although the disaster point was the interrupted rod arrangement, the core failure was in the communication between the fabricator and the designer. The designers had assumed that the drawings made by the fabricator were the final version and checked out. However, if anyone had actually recalculated the loadings, then it would never have got off the drawing board. The event became a cautionary tale for future construction projects and the hotel was reconstructed at a cost of around $5 million. Lawsuits totaling $3 billion were sought with only around $140 million being paid out over the following years. The design firm, Jack G. Gillam and associates in charge of the hotel's construction was found not criminally responsible, although this would be little consolation, as the company lost its engineering licenses in the states of Missouri, Kansas and Texas. Jack G. Gillam, haunted by the guilt of the event, would take lectures at universities showing the repercussions of his responsibility and the failings in construction of the hotel, hoping that others would learn from his unfortunate oversight. Thank you for watching.