What caused the collapse?
Here is a summary list of quality failings, all of which contributed to the collapse:
The structural engineers’ contract did not include on-site contract administration. Three times, they requested that they be commissioned to provide such inspection, but the project owners turned them down to save the cost.
The structural fabricators didn’t like the fastening methods specified by the engineers, so they changed them, in a way that doubled the load on the fasteners.
The fabricators testified that they advised the engineers of this change by telephone, and received approval. The engineers testified they never received this request, nor did they approve the change.
A set of shop drawings issued by the fabricator, and including the changes, was stamped and approved by the engineers.
Even if the design change had NOT been made by the fabricators, the fastening methods as designed were shown in court to be barely able to support the structural elements – and did not comply with applicable building code.
Except for the last two points, you might have concluded that the engineers were in the clear, and that the fabricators and/or the owner were at fault. Well, not quite. The engineers were found guilty of gross negligence, misconduct and unprofessional conduct, and their licenses to practice in that state were permanently revoked. Game over.
As usual in litigation, the facts are more mired in complexity than the simple summary above suggests. If you want to read more about the collapse of the atrium bridges in the Kansas City Hyatt – Wikipedia carries a good account (Google “Hyatt Regency Walkway Collapse”).
Another good article can be found in the Engineering Library: (http://www.engineering.com/Library/ArticlesPage/tabid/85/ArticleID/175/Hyatt-Regency-Walkway-Collapse.aspx).