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Good video on the possible cause of the collapse. The concrete pool deck was not sloped according to the plans. It was poured with no slope. This allowed water to accumulate and linger on the deck. The water found its way down into the concrete structure below and started rusting the rebar used to reinforce the concrete. When rebar rusts it expands. When rebar inside of concrete expands it pushes against the concrete and causes it to fail and break apart. This is called spalling. Concrete has great compressive strength but less shear or tensile strength. It looks like the condos dropped in four parts. The first section near the core of the building started dropping and it compromised each successive section causing the concrete to fail and the sections to topple.