Engineers studying the collapsed Florida tower said there seemed to be less steel reinforcement in certain areas than would have been expected from the 1979 design drawings.
Oh, oh, oh. That makes complete sense.
Text inset on photo: Engineers said that damaged columns at the collapse site appear to have less steel reinforcement than what the design drawings called for.
The rebar looks thin, doesn't it? Like pick-up sticks. That doesn't look like much reinforcement even to a layman.
Those columns were part of an exterior deck that served as a ground-level parking area adjacent to a pool plaza. It is a key point of interest, because at least two witnesses have said they saw part of the deck collapse in the minutes before the building toppled.
The condo tower’s 1979 design drawings... indicate that the vertical columns in many parts of the building were supposed to...[be] embedded with eight rods of reinforcing steel — four in one direction, four in the other — near the tops of the slabs. But the reinforcing rods in the parking area, left exposed in many places after the parking deck slab slammed down to the lower level, appear to be fewer in number.
Okay, so they don't look spaghetti-thin to the experts, just fewer in number. I stand corrected.
On most faces of the exposed slab, only two pieces of rebar can be seen, half of what would be expected. Three bars are visible on another.
Inset caption to left photo:Top steel reinforcing bars
Concrete can support tall buildings only when it is bolstered with steel reinforcement. Concrete is a strong material “in compression,” as engineers put it — in supporting weight above it, for example. But it is far less effective “in tension,” or holding things together when forces would tend to pull the concrete apart. Embedding steel adds that essential tensile strength, and sound design calculations, backed up by building codes, specify how much steel is needed, depending on the type, size and other features of a building.
Mr. [R. Shankar] Nair...a member of the National Academy of Engineering and former chairman of the Council on Tall Buildings and Urban Habitat...who has over 50 years of design experience, said it was clear from images of the three damaged columns that the structures did not appear to contain the expected amount of steel.
The design, he said, called for running a number of steel bars through the slab of the parking deck, at least four of which would thread in each direction through each of the columns that held both the garage and the rest of the structure on their shoulders. But photos show far fewer passing through the columns, he said.
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John Pistorino, a consulting engineer in the Miami area who has been in the industry for decades, said that in general, a city building inspector or someone hired by the builder would have examined the placement of steel before concrete was poured.
What? That seems to me absurd (with respect for Pistorino). I can say almost beyond a reasonable doubt that no goddamned city building inspector was standing over the "placement of steel before concrete was poured."
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During the collapse, the slab in question at Champlain Towers South, which was suspended in part on the three damaged columns that are still visible, fell to the parking level, one floor below ground level. Inadequate steel “could explain a slab failure — the slab letting go and dropping down,” Mr. Nair said. But he said he did not believe the tumbling slab could have been the initial cause of the larger collapse.
God, folks, they're still on some version of the DUI-driver-hit-a-post theory as the "cause." I will give a metaphorical corollary and then ask a practical question, both to indicate the irrelevance of this. Corollary: Why does a dead rotten tree in the forest fall when it does? There doesn't have to be an external cause, like a person leaning against it. Some trees just fall. The cause is the tree is dead and rotten and was going to fall at some point, with or without an external nudge. Trees fall in the forest all the time without warning. Foresters or hunters just hear it crash, that's the first sign they get. Practical: If we had uncontroverted proof (and we haven't any evidence of that) that a driver hit one of those critical posts and that that was the trigger for the collapse, what lessons to builders, architects, and engineers take from that? Bold signs,"DUI Drivers Do Not Enter"? To state the obvious, an impaired or incompetent driver in a parking lot should not be able to bring down a twelve-story building by running into a support post. Come on. But the experts will not get off this.
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This is new:
Gabriel Nir, who lived in Apartment 111, on the first floor of the portion of the building that collapsed, said he came home before 1 a.m. and noticed water pooling at the base of the entry ramp, although that was not uncommon. He did not see any rubble at that point, he said in an interview.
When he and his mother entered their apartment, they heard banging noises that sounded as if they were coming from above.
“We thought people were doing construction,” Mr. Nir said. They initially shrugged it off, but it continued for several minutes, growing more intense.
Mr. Nir said his mother went to the lobby to complain about the noise. He was in the kitchen making food when he heard loud rumbling and saw a cloud of dust coming from the area of the pool deck. He and his sister hurried to the lobby to join their mother and encouraged a security guard to call 911.
Then, walking outside, Mr. Nir saw that a part of the ground-level portion of the parking garage and pool deck — the part that engineers are now scrutinizing — had dropped. He also saw pipes bursting, he said, followed eventually by the collapse of about half the building. He and his family members ran from the site, surviving even as their condominium was crushed at the base of the collapse.
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The unexpectedly low amount of rebar visible after the collapse of the parking slab was not the only potential problem with steel reinforcement that engineers noticed in their initial reviews.
Dawn E. Lehman, a professor of structural engineering at the University of Washington, noted that rebar could be seen dangling from parts of the remaining structure, pulled clean from the concrete. She said that could indicate that in some places, the concrete was damaged and the steel might not have had a sufficient bond with the concrete. This could have several explanations, she said, including corrosion, concrete deterioration, shear damage to the concrete or the use of a type of reinforcing rebar with weaker bonding properties.
It does look like there was a bonding problem.
