Jeff Ostroff said:
1) I still don't see how that planter next to the wall could have caused the pool deck to break apart there and pull away from the wall,
1) The area of the parking deck that collapsed is essentially bounded by column line G.1 to the West and by column line K to the East. We know that the area of the parking deck West of column line G.1 did not collapse and most of the area of the parking deck East of column line G.1 did collapse, so there was a weakness or discontinuity north-south along column line G.1. We can see that the pool deck East of column line K has collapsed against the southern wall leaving the top surface of the deck concave, but the top surface of the parking deck West of column line K is convex, so there is also a discontinuity or weakness running north-south along column line K that extends from the southern property line wall north to somewhere between column lines 14 and 15.
We can observe cracks in the parking deck area between column lines G.1 and K that run generally east-west that are open at the top. So I think it is reasonable to conclude that the top surface of the deck failed in tension. The areas of deck to the north and south of the crack are lower than the crack. The question then becomes which area failed first, the area to the south of the crack or the area to the north? To understand the answer to that question we can consider the two scenarios in detail before the crack is formed and decide whether they are viable.
Scenario 1) the area of deck south of the crack first becomes unsupported. The collapse is progressing from the south to the north. In this case the area bounded by column line G.1, K and the southern wall is now supported by six columns, three along column line 14.1 and three columns along column line 14 / 13.1. The area of the deck south of column line 14.1 is supported in cantilever and the top surface is in tension. Some combination of loads and concrete strength in that area can allow the concrete to crack in the way we see. The area of deck north of the crack and north of column line 14 is sufficiently constrained by the three columns 23 feet to the north along column line 14 / 13.1 to resist rotation of the deck surface upwards. Scenario 1 is a viable condition to produce the top surface crack in tension we see.
Scenario 2) the area of deck north of the crack first becomes unsupported. The collapse is progressing from the north to the south. One or more of the columns along column line 14.1 between column line G.1 and K have punched through. The only remaining support for the parking deck is the connection to the wall and the deck is rotating downwards in the north. We know from sheet S12 of 14 (37 of 336) modified 1.17.80 to reflect change of pile type. That the typical retaining wall is 8” thick plus the concrete over the sheet pile, perhaps 16” total. The question becomes whether it is possible for the deck wall connection to offer sufficient resistance to downward rotation of the deck to the north to create the crack. In this scenario the stress is concentrated in the outside of the wall as the deck hinges on the front surface of the wall. The distance of unsupported deck from the hinge point to the north is at least 49 feet, the length of supporting concrete at the deck wall joint from the hinge point to the outside of the wall is 16 inches. The deck is only 9.5 inches thick but it has two pieces of rebar running horizontally the wall has one piece of rebar running vertically. The deck wall joint cannot offer sufficient resistance to the rotation of the deck to cause the crack we see. The deck wall connection would fail first, just as it did east of column line K. Scenario 2 is not a viable condition to produce the top surface crack in tension we see.
Since the area of deck south of the crack rotates down and the area of the deck north of the wall also rotates down, there must be a hinge point somewhere between the wall and the crack that allows the deck to retract from the wall.
Jeff Ostroff said:
Tha area was never mentioned as a problem area prior to the collapse,
In your helpful video “
Analysis Garage Video BEFORE Condo Collapse: Water Everywhere”
From 9:50-15:20 including the important advice at 10:35 “If you don’t tell water where to go, it will make up it’s own mind and it always picks the most expensive course of action”. There is lots of evidence of water damage. And that area of deck underside is stepped down, meaning the water can flow from column line K to the west via capillary action.
Jeff Ostroff said:
2) IF the slab separated from the south wall with cars on it, why did they fall back into the V-shape at the center of the slab (driving lane of the covered parking deck), instead of cars falling forward toward the south wall since the slab separated from the wall?
2) The deck cracked beneath the black pickup truck, its rear wheels dropped to the point the chassis bottomed out, column I14.1 punched through, column I14 punched through, other columns punched through, the deck impacted cars below and fractured [along the construction join?] between column lines 14 and 14.1. The cars didn’t move toward the south wall significantly because they were not between the crack and the wall and the angle of the deck was never steep enough to cause them to roll towards the wall.
