reinforced concrete. there is rebar inside. steel reinforcement that actually provide strength of the column, itself. think about this column, supporting huge about there. really strong. but once this get compromised by the -- specially the salt air. you it's rust. once rust, then the steel lose capacity and become weaker. also many cases actually compromise the concrete around it because that rust expands and lose the capacity that cause the collapse. >> yeah. i mean still so traumatic to think about. i know it's going to take many months to really get to that forensic level we know exactly what happened. kit miyamoto, thanks so much. really appreciate your expertise on this. >> thanks so much. >> and we'll be right back in a moment.