Stooo you left in a bad mood without one link!!!!
I found one for you .....
How long are skyscrapers built to last?This means we would expect a typical structure to fail once in every 500 to 1,000 years.
New buildings are not only designed to not fail, but are also designed so that in the event that they do fail, they will do so in a predictable and desirable (or at any rate, the least undesirable) manner. This is done to avoid sudden catastrophic failures. It is desirable that if a building is going to fail, that it fails in a ductile, non-brittle way that allows for occupants to exit before the collapse.
To visualise the difference, imagine a structure suddenly cracking, popping and entire floors falling and pancaking on top of one another – this is a brittle failure and is undesirable. Next, imagine a structure flexing and warping as the building distorts to redistribute loads, before finally giving out – in this scenario, occupants could exit the structure and move a safe distance away before collapse occurs.
https://www.independent.co.uk/arts-ente ... 63881.htmlThese things have been part of the safety issue for fifty years apparently but no buildings have been designed to self demolish into their own footprint and if they had the 911 commission would have been loud and clear about them.
Self imploding designs would kill more people than falling into the street.
The safety measures slow the rate of collapse giving as many people as possible time to get out. This clearly didn't happen with building 7 as it collapsed at freefall speed meaning every joint in I think seventy four structural beams would have to fail at exactly the same time .... only ever happens in a controlled manner.
Just half a dozen not failing out of the hundreds would have prevented freefall and telescoping into itself.