Lecture 14

Question 1

37. For the Hyatt Regency Hotel walkway collapse on the 17 July 1981 Figure 58 show the force diagrams for the original design to the hanger (left-side) and the option chosen to construct (right-side). Explain why the original detailing was impractical given that the walkway weighed 7 tons and the height difference between the 2nd and 4th floor walkways is 6.1m. Why did the constructed hanger detailing have a far too low resistance? Compare the connection load with the ultimate connection strength (in kN) by the Kansas City Building code? Explain why E – R > 0 was for connection failure. Loads to be given in kN

Answer 1

• The original design involved a series of steel rods susporting the walkway from the ceiling (shown in the left diagram). However during construction the design was changed to single rod supporting both walkways which doubled the load on the connection point.
• The original design distributed the load more evely across more support points. The bolts then had to bear the weight of both walkways. This increased the load at the connection points.
• The weight combined with the height created a large force acting on the connection points. The alterted design lead to an excessive stress on the connections
• The connection points were not reinforced to withstand the increased load. There was a lack of reinforcement and insufficient strength in the connection points
• The original design had the 2nd and 4th walkways suspended from the same
  continuous thread 32mm diameter rod and held in place by nuts. The design had the rod strength to be 413 MPa. The design was impractical as it then required the 4th walkway to be raised up by 6.1m without damoering the thread on which the supporting nut had to be tightened. The contractor modififed the design to two hangers without it being checked.
• The sketches shown in figure 58 show the change was to double (2P) the resultant force at the connection on the 4th floor walkway. The 4th floor was carrying the live loads from both walkways.
• The dead load was 8% higher than its normal design (81KN) but its calculated value was 73kN at 9UE ( the connection that failued) the live load with an estimated 63 people one was 9.3KN.
• The Kansas city building regulations required a design live load capacity of 108KN. Combinig dead and live loads allowable load is 181 kN ( 73+108). Allowable capacity would be at least 302kN for a FoS of 1.67. Actual load at time of failure was only 90kN,
• E – R > 0 mean failure. With R , resistance/ load capacity ranging from 72kN to 90kN with a mean of 81kN. And E imposed load/ effect of actions is 90kN. Then calculated = failure.
• This was the same for all connections. Failure of any one of the connections would have led to complete collapse.

Question 2

38. Connection 9UE was discovered to be the hanger that failed first and collapse was inevitable when his connector’s load (2P) could not be redistributed to the other five hangers holding the walkway up. How did it fail (Slide 14-9, 14-11 to 14-14, F)? What simple modification to the 9UE connection detailing between the rod and transverse beam would you have made to design out the observed mode of failure from happening

Answer 2

• The connection failed due to being overloaded. The failure initiated when the bottom longitudinal welds near the ends of the 4th floor box beams fractured and the bottom flanges deformed sufficiently to permit the box beam to slip down over the nut and washer at the lower end.
• The force could not be redirtibuted down another rod therefore the lack of reduencey caused the collapse.
• Modification could have occurred on the connection point between the rod and the transerev beam. Could have increased the size or the number of bolts used to secure the connection which provides additional shear strength. The addition of reinforeced plates or brackts could have been added to distribute the load more evenly across the connection and reduce stress.