Yulya, as far as "controlled" collapse. Well, that's simple. According to OSHA (Occupational Safety and Health Administration) regulations effective August 1, 1968, all buildings over 120 feet high must be ASSEMBLED not built. That means that ready to connect pieces are placed together by heavy bolts and then wired together. If the wiring is heated sufficiently or in the even that structure is compromised, the building will collapse straight down one level of bulks at a time, which is exactly what happend. Note the law came out in 1968, WTC was built in 1975. This law exists exactly for that reason, in the event of emergency the building will collapse with minimum damage and will not fall side way like solid buildings such as for example Empire State building. If this was Empire State hit, it would have taken out half Manhattan.