2018 report recommended $9 million in repairs to building
Four days after the collapse of the Champlain Towers, the chances of finding survivors in the rubble has diminished. Demands for answers grows louder. We’ll round up questions here and answer them as best we can.
When were the Champlain Towers built?
The Champlain Towers South Building was built in 1981.
Had there been reports of structural problems in the Champlain Towers?
A 2018 report showing the need for repairs to much of the building has been getting a lot of attention after the collapse. The report, prepared by Morabito Consultants, was requested to prepare for an upcoming 40-year recertification of the building. It was received by the Champlain South Condominium Association. The consulting firm found “failed waterproofing causing major structural damage” to concrete below the pool deck and a drain that was not draining properly. The inspection documented “abundant cracking and spalling of varying degrees … in the concrete columns” in the parking garage where the collapse appears to originate, according to civil engineers who have been playing back the collapse filmed by a security camera on the adjoining property. Nevertheless, the report concludes the “general alignment” of the structure is “good,” the highest rating.
Perhaps most damning is the potential of water damage to the concrete slab on which the entire building rests. “Many of the existing pavers on the pool deck are cracked and showing moderate wear and tear from years of being exposed to the elements.” “The joint sealant was observed to be beyond its useful life and are in need of complete replacement.” Also, “the waterproofing below the pool deck and entrance drive as well as all of the planter waterproofing is beyond its useful life and therefore must all be completely removed and replaced. The failed waterproofing is causing major structural damage to the concrete structural slab [emphasis ours] below these areas.”
“Failure to replace the waterproofing in the near future will cause the extent of the concrete deterioration to expand exponentially. “
The report also notes the “entrance drive/pool deck/planter laid on a flat structure. Since the reinforced concrete slab is not sloped, the drain, the water sits on the waterproofing until it evaporates.”
“MC recommends that the entrance/pool deck concrete slabs that are showing distress be removed and replaced in their entirely.”
“Most of the concrete deterioration needs to be repaired in a timely fashion.
Residents also complained of standing water in the below-grade garage even when it hadn’t rained.
Why were the recommendations of the 2018 report not acted on right away?
This seems to be the biggest question post collapse. Perhaps the expense predicted was so great ($9 million) and the threat deemed not imminent. Condo owners were told they would be assessed the cost of repairs in proportion to the size of their condos, the average assessment about $100K, and the owners had secured a line of credit to start the repairs.
A repair crew was working to repair the roof the day before the collapse. Could that have contributed to the collapse?
This is flatly denied by the repair crew, who say there simply was not enough equipment or supplies on the roof to matter. Also, educated observers of the video of the collapse, included structural engineers on our Eng-Tips forum, are in agreement that the collapse started at the bottom of the building.
In light of the disaster, a 40-year recertification period does seem too long. How did it get to be 40 years?
Miami Dade County demands commercial and multi-family residential buildings to undergo a recertification 40 years after construction. A Drug Enforcement Agency building (DEA) in downtown Miami collapsed in 1974 killing 7 federal employees. A newly licensed engineer working for the county was tasked with writing a report and making recommendations to prevent future disasters. The building was about 40 years old – and that became the time after which future buildings in Miami-Dade County would be recertified. The 40-year recertification has been adopted by many Florida governments, including Broward County to the north and Surfside.
The buildings must be reinspected every 10 years after the 40 year certification.
Has this type of collapse happened before in the area?
A similar building collapse happened just down the road 3 years ago. The building was vacant. A construction worker is injured in the collapse. Warning: Mute to avoid hearing f-bombs from startled construction workers.
Just 2.3 miles down Collins Avenue from the Champlain Towers, the Marlborough House, a residential high-rise tower, collapsed prematurely in July 2018. It had been scheduled for demolition but the building couldn’t wait. Luckily, tenants had been vacated. One construction worker was killed. Similar to Champlain Towers, the lower floors gave way first and progressive failure of all the floors followed — a classic pancake failure.
Was the building secured with pylons?
All of Surfside, a town of 5700, sits on top of a barrier island. Beneath the sand lies highly porous limestone, the after product of coral beds, and underneath that, bedrock. It is not known whether the pilings reached bedrock or are merely in limestone.
“My understanding is they sink pilings down into the rock, but lime rock is not a strong rock,” says James Englehardt, an environmental engineering professor at the University of Miami Englehardt in USA Today. said. “It’s friable, even in your hand.”
What is pancaking?
Pancaking is a type of progressive failure where floors descend catastrophically in parallel. It is the most dangerous of collapse for occupants as it leaves the least “survivable space,” or voids in which people could be saved and found. It is the preferred outcome of a controlled demolition, as floor after floor is stacked neatly (like pancakes) and has the least chance of damage to the surroundings.
To pancake a building, don’t all columns have be blown at the same time?
In a controlled demolition, the charges are blown simultaneously, the charges detonating from the same signal. This ensures floors lose all their vertical support at once, and the floors descend, don’t tilt, the tower doesn’t bend over, crashing on its neighbor. It is harder to imagine columns could be simultaneously crippled from corrosion or compression.
But they don’t have to be simultaneous, just close enough.
The World Trade Center also exhibited pancake failure. A fire that would weaken the columns could have failed all at once, only close enough. A floor that loses one support would put more of a load on the remaining supports. The remaining supports, if already compromised and weakened, may not withstand the suddenly increased load. A 33% load increase (as it would be if 3 columns out of 4 remain) may be less than the factor of safety of a healthy column but a weakened column could easily fail. The floor will bend and tilt as columns finish giving out – but not enough to matter. After a floor collapses on the floor below, the impact will be enough to overcome all the columns of the weakened floor. A domino effect occurs and every floor falls flat to the ground.
A 2020 report showed subsidence in the area of the Champlain Towers What is normal rate of subsidence and when should you worry?
Subsidence of even a few millimeters a year can add up to inches over time, plenty to cause buildings and structures to rack, overstressing concrete. The areas of concern in Miami beach were found to be between 1.9 and 2.3 mm per year. This pales in comparison to Mexico city, where subsidence is 20 inches per year.
What could have caused the sinking detected by the satellites in the 2020 report?
The satellite measuring the distance would detect the surface of the ground or the top of a building. The lowering detected could have been caused by subsidence, a creeping structural collapse or a combination of the two.
What is the resolution and error in the satellite measurement?
Light wave interferometry is one of the most accurate forms of measurement invented. Large distances can be measured to within fractions of a millimeter as was done by the 2020 report.
