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1 Failure Analysis: Mechanical Engineering University of Florida [a.bonkovski@ufl.edu] Contents

2 I. Abstract ……………………………………………………………………………………………………………………………………. 3 II. Introduction ……………………………………………………………………………………………………………………..…… 3-4 III. Types of Failures in Mechanical Engineering ……….……………………………………………………………………. 4 a. Wear & Tear ………………………….…………………………………………………………………………………..… 4 b. Corrosion ……………………………………………………………………………………………………………………… 5 c. Fatigue …………………………………………………………………………………………………………………………. 5 d. Impact Damage ……………………………………………………………………………………………………………. 6 IV. Methods of Failure Analysis ……………………………………………………………………………………………………… 6 a. Destructive/Non-destructive ……………………………………………………………………………………….. 6 b. Industry standards for materials and testing ………………….…………………………………...………. 7 V. Cases of Failure ………………………………………………………………………………………………………………………… 7 a. Case Description ………………………………………………………………………………………………………….. 7 b. Case Investigation ………………………………………………………………………………………………………… 7 c. Recommendations ………………………………………………………………………………………………..…….. 7 VI. Conclusion ………………………………………………………………………………………………………………………………… 8 VII. References ………………………………………………………………………………………………………………….………. 9-10 Table of Graphics Figure 1 Timeline of the major events that led to the collapse ................................................................... 5 Figure 2 The process of wear and tear of metals at the microscopic level .................................................. 5 Figure 3 Corrosion failure of metal .............................................................................................................. 6 Figure 4 Failure is apparent due to the sudden change in material that was broken off due to fatigue ..... 6 Figure 5 Ultrasonic Testing .......................................................................................................................... 7 Figure 6 Tensile Testing ............................................................................................................................... 7 Figure 7 Equation for Factor of Safety ......................................................................................................... 9

3 I. Abstract The Hyatt Regency Walkway Collapse, which took place on July 17, 1981, in Kansas City, Missouri, serves as a prime example of the horrific outcomes that may arise from slight engineering errors. This tragic incident serves as one of the deadliest structural disasters in American history, having a death toll of 114, and hundreds more were severely injured. This paper provides a brief summarization of the design problems within the walkway’s suspended structure and the crucial impact design alterations played on the safety of the walkway. In addition to highlighting the change in building codes and professional standards in the engineering and construction industries, this paper also examines the legal ramifications that the engineers and contractors faced after the tragedy occurred. This paper highlights the crucial value of proper engineering design, excellent communication, and stringent quality control in building projects. As a crucial reminder of the responsibility that engineers face in maintaining the safety of the built environment, the lessons learned from this disaster will forever have an impact on the world of engineering. II. Introduction The hotel party that transformed into a sheer and utter tragedy, the Hyatt Regency Walkway Collapse, occurred on July 17, 1981. The collapse resulted in 114 deaths, 216 non-fatal injuries, and mental trauma such as survivor’s guilt being inflicted on the others involved [1]. The engineering failure behind the tragedy stemmed from both the design phase and the construction phase. Once the design was completed, the failure progressed through the individual elements of the bridge and the hanger rods responsible for the suspension of the structure [2]. NBS later caught a mathematical error that determined that the rods and box beams used to hold up the walkways were bound to fail, as they were advertised to support far more weight than physically possible [2]. Even though there were a multitude of times when the mistakes could have been caught, they were missed due to the lack of attention to detail from the engineers involved. Communication between the engineers and the project manager was minimal and was based upon the ‘honor code’, with little to no verification of mathematical details that were essential to the design and construction of the structure [3]. The fourth-floor hanger rods caused the initial spark of

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4 complications, as they did not have the strength to support the fourth-floor walkway, as well as the tension from the second-floor walkway [4]. Another issue with the hanger rods is that their build did not satisfy the provisions under the Kansas City Building Code [4]. Certain AISC specifications are found within this code, describing the shear and tensile stresses that the hanging rods can handle. According to section 1.5.2 of the AISC allows for a tensile stress force in the y-direction at a magnitude of 0.60 [5]. The box beam-hanger rod connections were altered halfway through the build process since the initial design did not pass the Kansas City building code. However, the alteration ultimately failed as well. The offset beams did not reach proper equilibrium throughout the building, and the tension that the second- floor walkway imposed onto the fourth-floor walkway became unbearable for the ceiling to hold up [6]. This led to the fourth-floor walkway collapsing, followed by the collapse of the second-floor walkway, which then crashed down onto the lobby of people enjoying a tea party. After further inspection, the collapse began far before the actual tragedy occurred. Due to its flawed design, the roof had partially collapsed into itself since it could barely hold up the skywalks without the applied force of people walking across it [7]. The tragedy that occurred should be used as an impetus to modify engineering practices and mold them into the orientation of placing public welfare and safety first. While this was a horrible event for society, it was a good opportunity for the engineering world to reevaluate its purpose and responsibilities [8]. Figure 1 Timeline of the major events that led to the collapse III. Types of Failures in Mechanical Engineering a. Wear and tear are critical aspects of engineering as it they impacts impact the performance of a structure. Among the wear-and-tear forms of failures, there are three

5 categories under which certain situations fall under . Adhesive wear occurs when two materials in close contact slide along, causing imperfections between themselves [9]. Abrasive wear occurs when two distinct materials come in contact, one being softer than the other, which causes the harder surface to wear down the softer one [10]. Erosive wear occurs when a constant flow of fluid continuously wears down the material. The engineers were concerned with the wear and tear of the rods, therefore, so they increased the number of structural rods from one to two. Figure 2 The process of wear and tear of metals at the microscopic level b. Corrosion is the process that involves metal degradation due to chemical or electric reactions that occur [11]. This process can lead to a loss of proper material function and structural cracking, which in most cases can lead to catastrophic instances, such as the Hyatt Regency Walkway Collapse [1]. Figure 3 Corrosion failure of metal c. Fatigue failure is the formation of cracks due to a repetitive load that must be carried by the structure [12]. Similarly, the hanger rods supporting the walkway to the ceiling gradually collapsed due to fatigue failure and lack of support from the constant pressure of the walkway [7].

6 Figure 4 Failure is apparent due to the sudden change in material that was broken off due to fatigue Figure 5 Failure is apparent due to the sudden change in material that was broken off due to fatigue d. Impact damage failures are unavoidable; however, the effects can be minimized by engineers behind the design. Using stronger composites to build your structures decreases the likelihood of destruction when the structure is braced with impact [13]. Impact damage varies among where the impact occurred, as well as how strong the force was. e. f. IV. Methods of Failure Analysis a. When performing failure analysis, the proper execution is to perform a preventative test and a forensic test. The forensic test typically occurs after something went wrong. Notoriously, the engineers of the Hyatt Regency Walkway Collapse did not perform preventative tests on the final form of the built structure [14]. The forensic tests were broken down into two forms: destructive testing and non-destructive testing. Among the non-destructive tests, ultrasonic testing was performed by the scientists at the scene. This form of testing sends high frequency high-frequency sound waves through the structure of a material to determine any informalities within the structure [15]. Destructive testing for the tragedy consisted of tensile testing. Tensile testing assesses the quality and strength of the material by pulling samples [16].

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7 Figure 6 Ultrasonic Testing Figure 7 Tensile Testing b. Following the Hyatt Regency Walkway Collapse, precedents were set in order to avoid these catastrophes from occurring again in the future. Certain standards that were set in place included increased emphasis on design and planning, construction testing, and preventative testing [17]. V. Cases of Failure a. The Hyatt Regency Kansas City Hotel was a luxury hotel featuring the unique and striking design of walkways suspended from the ceiling [1]. On July 17, 1981, a dance was taking place within the vast lobby of the hotel. The party took a turn for the worse when the two walkways simultaneously collapsed onto the crowd below, killing 114 and injuring 216 more [4]. The primary cause of failure was the design of the box-beams, which carried the loads of both walkways. After a design change during the construction phase of the project, the engineers decided on using two sets of box beams, rather than one [6]. b. Following the disaster, an extensive investigation began as scientists scoured the premises to find out how it all went wrong. The National Bureau of Standards conducted a complete investigation of the disaster, concluding that the failure occurred due to the change in design plans [7]. This proves that even the most minor decisions may have a catastrophic impact on society. This tragedy will forever serve as a sobering reminder of

8 the importance of adherence towards engineering’s practices that are put in place to ensure public safety and welfare. c. Along the complete timeline of the design and construction of the Hyatt Regency Walkway’s, many mistakes were made. The design integrity and last-minute changes were what ultimately led to the physical collapse, but many other actions contributed to it [8]. Proper oversight and usage of materials may have also been an altering factor in the design phase of the structure. The structure was notoriously referred to as ‘not meeting the safety expectations’, therefore, building the structure with materials that exceeded those expectations could have avoided the catastrophe [6]. These recommendations play a massive part in hindsight bias, bias; however, it is essential to note that while this tragedy was a horrifying day in history, it was a well-needed wake-up call for the engineering community. VI. Conclusion After the analysis of the mistakes made along the way, it is clear that there are certain areas that could certain areas could have been altered in order to to avoid the tragedy. First off, the usage of the two box-beam rods was a clear mistake, throwing off the equilibrium point of the forces. By changing Changing the equilibrium point, this added another point of stress forced onto the walkway, being the connection point between the two beams, as well as the ceiling [11]. This theory is backed by the equation of the maximum tensile stress theory. Also known as the Guest Theory, it is used to predict the failure of a material under certain conditions of stress [18]. To put it into perspective, by By adding the extra beam, the engineers have added another point of stress that now increased area that inherits forces acting from both sides in order to to reach equilibrium , resulting in reduced axial stress [19]. After a certain point of tensile stress is inflicted, it is as if a human is being pulled from their arms from both directions, which is not a sustainable force the material used reaches its yield strength w here the beam begins necking , then ultimate tensile strength, resulting in a deformed or fractured beam . An additional critical component that the engineers did not take into consideration was the structure’s Factor of Safety (FoS).

9 Figure 8 Equation for Factor of Safety Within the equation, the ultimate strength refers to the maximum stress and forces the structure can possibly withstand before prior to failure [20]. The Maximum expected load or stress is as it sounds: the stress that a structure is expected to encounter during normal operations [20]. When these two numbers are applied into a ratio, the resultant gives you The ratio of these two numbers indicates how strong the structure may be the reliability of a structure . If the equation gives you yields a 3:1 ratio, the structure is expected should to handle 3 times the maximum expected load. Figure 9 Equation for Factor of Safety VII. References [1] R. Bernhardt, “Hyatt Regency Walkway Collapse: Evaluation of the Box Beam Design”, xxxxx Forensic Engineering 2018: Forging Forensic Frontiers, vol. 8, issue 11, pp. 447-456, xxxxx Nov. 2018. [2] P. D. Moncarz and R. K. Taylor, “Engineering process failure—Hyatt Walkway collapse,” Journal of Performance of Constructed Facilities , vol. 14, no. 2, pp. 46–50, May 2000.

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10 [3] G. P. Luth, “Chronology and context of the Hyatt Regency collapse,” Journal of Performance of Constructed Facilities , vol. 14, no. 2, pp. 51–61, 2000. [4] E. A. Banset and G. M. Parsons, “Communications failure in Hyatt Regency disaster,” Journal of Professional Issues in Engineering , vol. 115, no. 3, pp. 273–288, Jul. 1989. [5] Q. Zhao et al. , “High-strength titanium alloys for aerospace engineering applications: A review on melting-forging process,” Materials Science and Engineering: A , vol. 845, p. 143260, 2022. [6] W. M. Roddis, “Structural failures and engineering ethics,” Journal of Structural Engineering , vol. 119, no. 5, pp. 1539–1555, May. 1993. [7] R. D. Marshall, E. O. Pfrang, E. V. Leyendecker, and K. A. Woodward, Investigation of the kansas city hyatt regency walkways collapse , May. 1982. [8] R. A. Rubin and L. A. Banick, “The Hyatt Regency Decision: One view,” Journal of Performance of Constructed Facilities , vol. 1, no. 3, pp. 161–167, Aug. 1987. [9] C. R. Gagg and P. R. Lewis, “Wear as a product failure mechanism – overview and case studies,” Engineering Failure Analysis , vol. 14, no. 8, pp. 1618–1640, Dec. 2007. [10] M. A. Moore and F. S. King, “Abrasive wear of brittle solids,” Wear , vol. 60, no. 1, pp. 123–140, Apr. 1980. [11] J. Sun, S. Chen, Y. Qu, and J. Li, “Review on stress corrosion and corrosion fatigue failure of centrifugal compressor impeller,” Chinese Journal of Mechanical Engineering , vol. 28, no. 2, pp. 217–225, Sep. 2015. [12] S. M. Marco and W. L. Starkey, “A concept of fatigue damage,” Journal of Fluids Engineering , vol. 76, no. 4, pp. 627–632, Jul. 1954. [13] S. L. Angioni, M. Meo, and A. Foreman, “Impact damage resistance and damage suppression properties of shape memory alloys in hybrid composites—a review,” Smart Materials and Structures , vol. 20, no. 1, p. 013001, Apr. 2010. [14] M. Manion and W. M. Evan, “Technological catastrophes: Their causes and prevention,” Technology in Society , vol. 24, no. 3, pp. 207–224, Aug. 2002. [15] F. Honarvar and A. Varvani-Farahani, “A review of ultrasonic testing applications in additive manufacturing: Defect Evaluation, material characterization, and Process Control,” Ultrasonics , vol. 108, p. 106227, Dec. 2020. [16] H. W. Reinhardt, H. A. Cornelissen, and D. A. Hordijk, “Tensile tests and failure analysis of concrete,” Journal of Structural Engineering , vol. 112, no. 11, pp. 2462–2477, Nov. 1986.

11 [17] C. B. Wilkinson, “Aftermath of a disaster: The collapse of the Hyatt Regency Hotel skywalks,” American Journal of Psychiatry , vol. 140, no. 9, pp. 1134–1139, Sep. 1983. [18] E. Z. Lajtai, “Effect of tensile stress gradient on brittle fracture initiation,” International Journal of Rock Mechanics and Mining Sciences & Geomechanics Abstracts , vol. 9, no. 5, pp. 569–578, Sep. 1972. [19] K. Hayashi and S. Sasa, “The law of action and reaction for the effective force in a non- equilibrium colloidal system,” Journal of Physics: Condensed Matter , vol. 18, no. 10, pp. 2825–2836, Feb. 2006. [20] T. Xing and F. Stern, “Factors of safety for Richardson extrapolation,” Journal of Fluids Engineering , vol. 132, no. 6, Jun. 2010.