Civil Engineering Case Study

Background

The collapse of two suspended walkways in the Kansas City Hyatt Regency Hotel on July 17, 1981 was one of the worst structural failures in United States history.  The disaster left 114 people dead and over 200 injured.  You have been hired to evaluate the disaster and determine whether the design was proper.

The suspended walkways are shown in Figure 1.  The fourth-floor walkway (top right in Figure 1) collapsed and fell on the second-floor walkway (bottom right in Figure 1).  The third-floor walkway, on the left in Figure 1, was not involved in the collapse.  Each walkway is about 120 ft long and 18 ft wide.

Figure 1: Walkways Before the Collapse (source: Pfrang and Marshall, 1982)

Each walkway consists of four main parts: two stringers (I-beams running along the length of each walkway), three box beams (running across the width of each walkway), a concrete deck (providing the walkway surface), and six threaded hanger rods (each 1.25 inches in diameter) passing through the box beams.  The box beams rested on washers and nuts attached to the hanger rods.  The fourth-floor walkway collapsed when the washers and nuts pulled through the box beams.  In Figure 2, a stringer is shown in the foreground running left to right, a box beam is in white running perpendicular to the stringer, the deck is shown above the box beam in the cutaway, and a hanging rod is shown in white running up and down.


Figure 2: Cutaway of a Walkway (source: Pfrang and Marshall, 1982)

In the original design, the hanger rods were continuous and ran from the ceiling to the bottom of the second-floor box beams.  During construction, change orders were suggested and approved to change the hanger rod configuration.  Each continuous rod was replaced with two rods - one running from the ceiling to the bottom of the fourth-floor box beams and one running from the top of the fourth-floor box beam to the bottom of the second-floor box beam.  The "as-built" hanger rods are shown in Figure 3.


Figure 3: Reconfiguration of Hanger Rods (source: Pfrang and Marshall, 1982)
 
 

Case Study

**Important Note: Please see the appendix for additional information and hints on performing the calculations***

In the case study, you are charged with investigating the Hyatt Regency disaster.  Specifically, your consulting firm has been hired to analyze three aspects of the disaster.  First, you must determine whether the capacity of the walkway as designed was greater than the design load.  Second, you are to perform experiments to determine whether the change order resulted in an increased load at the point of ultimate failure.  Third, you must determine whether the capacity of the walkway was greater than the actual load.

Please summarize your findings in a two-page report.  Your report should follow the following outline:
 

            Include: Title, group member names, group number, lecture section name, and date             Write a short (one or two paragraph) description of the walkways, disaster, and questions you are answering in the report.             Discuss the analysis method you used.  What principle did you use in your analysis? (Hint: What did you balance?) Briefly describe the experiments you performed to determine whether the change order resulted in an increased load at the point of ultimate failure.             Organize this section by the three areas you were charged with investigating.  For each question, present the results of your calculations and/or experiments.  Use tables to organize your calculations.  After presenting the analysis or experimental results, clearly answer the question.  When comparing the design capacity and design load, calculate the saftey factor and comment on whether it was big enough.  Also calculate the safety factor as built and comment on its magnitude.             Summarize your findings in one or two paragraphs.  Please comment on how errors such as the ones encountered in this case study could be avoided in the future.

In addition, 15 points will depend on the quality of your technical writing.  For full credit, be sure to avoid spelling and grammatical errors.  Use headings to show the structure of your report.  Refer to tables and figures in the body of the report.  Make sure tables and figures have numbers and titles.  Include units on all numbers.

Other Resources


For more information on the ethical aspects of the case, see this site .

For more photographs, go here and click on "Hyatt Regency Walkway Photographs" or "Miscellaneous Hyatt Regency Walkway Photographs"

For more technical information, see E.O. Pfrang and R. Marshall, "Collapse of the Kansas City Hyatt Regency Walkways", Civil Engineering, 65-68, July, 1982.
 
 

Appendix

    Introduction

To answer the case study questions, you must calculate the capacity (strength) of the walkway, load, and code requirements.  Civil engineers sometimes express capacities and loads in units of kips.  One kip = 1000 lb of force.  An object that weighs one ton (2000 lb) exhibits 2 kips of force.

    Capacity

The calculation of capacity is a bit difficult.  In this case study, assume that the capacity of the box beams was about 115 kips.

    Load

The total load is the sum of the dead load and live load.  The dead load comes from the construction materials.  For the fourth floor, the construction materials are the stringers, box beams, and deck (ignore the rods).  To calculate the weight of the stringers and box beams, you need to know a bit about how steel is designated.  The structural shape is given in a designation that includes the shape, depth, and weight.  For example, W30 x 132 means a wide flange beam (W = wide flange beam), about 30 inches deep, with a weight of 132 lb per foot of length.  For the walkways, the stringers were W16 x 26 steel and the box beams were made of two MC8 x 8.5  pieces (MC = flanged channel beams).  The deck was 3-1/4 in thick.  Assume the density of concrete is 150 lb/ft3.

The live load comes from the people on the walkway.  Video taken before the collapse showed about 80 people on the fourth-floor walkway.  Use a reasonable value for the average weight of the people.

      Safety Factor

The safety factor is the capacity divided by the load. A typical safety factor for a walkway is 1.67.  This means we want a capacity at least 1.67 times the total load.  You may wish to calculate the safety factor for the walkway as designed and walkway as built.