The SCI 301 Puzzler

This puzzle comes from an actual incident. In the original design for interior walkways in a hotel lobby, two walkways were to be suspended by single beams. A single pin attached the walkways to the beams as shown in the first diagram. The single pins were designed to withstand the shear forces created by the weight of the walkways. However, the long beams were difficult to manipulate during construction. The design was changed to use two shorter beams, again using the same single pin, one at the top of the bottom beam and one at the bottom of the top beam. Those who were in charge at the site thought the change was not significant. They were tragically wrong and approximately 100 people lost their lives. The beams themselves were of more than adequate size. The failure was in the pins. Which of the pins failed and why? (A carefully drawn free body diagram is all that is necessary to solve this puzzle.)

BE SURE to enter your full name. Enter your email address and CHECK that it is correct! Responses should be brief but complete. You must click the SUBMIT button to submit your entry. (You should receive a "Thank You" reply almost immediately.) Entries are due by noon on Monday of next week.
NOTE: Only your first submission will be accepted!