Ah yes, a classic exampl
e used in every engineering
course. On July 17, 1981, the walkways in the Hyatt Regency
in Kansas City
collapsed, killing 114 people and injuring another 200. The hotel had been just completed a few years earlier, and was considered a state of the art hotel
and convention center. The design included a large atrium
for parties and other functions, with suspended walkways connecting the hotel
rooms on the 2nd and 4th levels. On the night of July 17th, a dance
competition was held in the atrium with approximately 2000 guests in attendance. While most were on the ground floor, many were on the walkway
s dancing and watching the competition
. At approximately 7:05 pm, a loud crack was heard and the 2nd and 4th floor walkways collapsed and fell to the ground. So what went wrong?
The design for the walkways was done by Gillum-Colaco International Inc. The plans for the atrium walkways were to utilize steel rods hanging down from support beams at the top of the atrium. The rods would go through the walkways and be supported by large nuts on the underside of the walkway support beams. This is a solid design, unfortunately it was not built that way. The contruction company changed the drawings before building, due to difficulties in building it as planned. What it boiled down to was that in order to implement the design, they would have to thread the entire length of the steel rods so that nuts could be used underneath both walkways. To get around this, the design was changed so that only the ends would have to be threaded.
The modified design used one steel rod to go from the ceiling beams to the 4th floor walkway. To support the 2nd floor walkway, a 2nd beam was attatched to the 4th floor beams, approximately 4" inside of the bolt point for the ceiling support. Somehow, the design firm was not notified of this change and did not review the drawings before construction. Had they caught it, many lives could have been saved that night.
The problem with this design is that it will increase the load on the ceiling supports by about 2 times because the bolt holding the support cable to the ceiling also has to support the full weight of the lower walkway. Think of it this way, imagine two people hanging from a rope. Now, if both people are hanging on the rope, one above another, everything will be fine because each uses their own hand strength to hold themselves on. Assuming the rope is strong enough, and they have enough grip, it's all peachy. Now, imagine that instead one person is hanging onto the rope and the other person is hanging onto the first person's leg. In this case, the 2nd person still only has to hold on to their own weight, however now the first person has to support the weight of both persons. This is what happened with the modified design, the bolts holding the rods to the upper walkway had to support the weight of both walkways instead of just the upper one. In addition to this, the fact that the two rods were connected some distance appart applied a moment to the upper beam, further increasing the load on the bolts. Under this much stress, failure was inevitable.