Because it is difficult to say which of the lower segments of rebar would have passed through the columns, and therefore be visible in the wreckage after the slab fell, some engineers have so far focused on the upper bars. . The most important clues to what happened are probably still buried in the rubble.
“We have a whole bunch of issues that we think could be part of or the trigger for what happened,” Kilsheimer said.
The surprisingly small amount of rebar visible after the parking slab collapsed wasn’t the only potential issue with the steel rebar that engineers noticed during their first examinations.
Dawn E. Lehman, professor of structural engineering at the University of Washington, noted that rebar could be seen hanging from parts of the remaining structure, removed from the concrete. She said this could indicate that in some places the concrete was damaged and the steel may not have had sufficient adhesion with the concrete. This could have several explanations, she said, including corrosion, deterioration of concrete, shear damage to concrete, or the use of a type of rebar with weaker bond properties.
Mr Kilsheimer said he hoped to take a closer look at the rest of the building in the coming days, in order to better assess its components. Some fear that the remaining structure poses a danger. Mr Kilsheimer said a computer analysis suggested the northern part of it could be at risk of collapsing in high winds.
The building’s concrete and steel will eventually be tested, Kilsheimer said, and investigators will go underground to examine the soil and test the area with boreholes. They will model the building with computers and assemble the components recovered from the rubble in an off-site storage facility.
Solving the mystery, he said, is like starting with several puzzles, “throwing them in the air, mixing them with a broom, then trying to figure out which piece is which puzzle.”
Lazaro Gamio contributed reporting from Surfside, Florida.