Teschler on Topic
Leland Teschler • Executive Editor
Engineers of all stripes have developed a sudden interest in building construction practices thanks to the collapse of Miami’s Champlain South Tower. There’s been a lot of speculation about the tragedy’s cause, but one of the most interesting attempts at analyzing the sequence of events is an animation on YouTube developed by South African architect Mike Bell. After a little over a week, the video has attracted well over a million views.
Bell, whose design work includes the Mbombela 2010 World Cup stadium, says much of the data for his animation comes from publicly downloadable documents made available by the city of Surfside. Those documents include structural and architectural drawings, engineers’ inspection reports from 2018, and permit drawings of the substantial repair work scheduled to take place on the building.
“There is a substantial amount of visual information including video footage and still photography from the collapsed building which is wealth of information,” he told us by email. “Eyewitness accounts around the timing of events provide crucial clues. There are further conclusive clues in the layout of the rubble pile. Viewing the structure in the 3D model inevitably adds additional clarity. You discover things not apparent from looking at the plans. I discussed these clues with structural engineering colleagues who offered insights and concurred with my analysis.”
Bell’s Surfside animation, done in an open-source 3D graphics tool set called Blender, begins with a column failure of the pool deck where a structural column punches through the pool deck concrete slab. “(Column punch through) is typically where the slab-to-column area is too small, and the steel reinforcement bars are inadequate to hold the concrete to the column, so the slab drops. It is a rare occurrence and unforgivable in buildings,” Bell writes.
In Bell’s animation, columns punch through the pool deck one after another. The sagging pool deck then buckled the beams holding up the apartment building.
Bell gleaned a lot of information from where the slabs appeared to fail. “From photos it appears the slab failure lines are at construction joints in the concrete slab,” Bell writes. “Concrete is poured in sections called pours. These are the practical amount of concrete that can be cast in one go. At the edges of each pour a shaped keyed joint is made between sections. The keyed joint is visible in site photos. This is normal building procedure and creates an inevitable weak point in the structure which is usually mitigated with additional reinforcement.”
“It is highly likely this joint opened slightly over 40 years which was enough to let water from the failing waterproofing corrode and weaken the steel in the slab,” Bell continues. “Long-term wind action would have further weakened this joint. There is an excellent chance this joint was the initial trigger. The pool deck slab failed at the joint. The sheer mass of the slab pulling hard on the ground- floor slab edge of the building mortally wounded several columns supporting the tower section until the structure was compromised and it catastrophically collapsed. From trigger to collapse took roughly 45 minutes.”
Once the central portion of the structure collapses in Bell’s animation, a stair wall briefly stabilizes the east portion, and an elevator shear wall prevents the west part of the building from collapsing. “All buildings must have large, flat vertical structural elements that resist the substantial sideways forces produced by hurricane force winds and earthquakes. In this case, there were two shear walls. The larger one at the elevator was substantial enough to arrest the collapse of the western third of the tower.”
Of course, Bell’s animation is merely a “suggestion” about what happened, as he puts it. But it is unquestionably food for thought in light of the pervasiveness of its design. “Champlain Tower South was a typical design for apartments with a parking garage and pool deck and is replicated in Florida and around the world,” Bell writes. “There wasn’t anything unusual about this project.”
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