Medical Tuesday Blog

The Leaning Tower of San Francisco is outperforming the Leaning Tower of Pisa

May 30

Written by: Del Meyer
05/30/2017 6:42 AM 

San Francisco’s newest high rise has tilted 6 feet in 6 years.

The Leaning Tower of Pisa is more than five meters off perpendicular after 800 years.

The leaning tower of Pisa is located next to the Cathedral of Pisa, in Piazza dei Miracoli (Square of miracles) in the city of Pisa, Italy. It was constructed over two centuries starting in 1173 and finished in 1399. It was originally 60 meters high.  It has sunk unevenly so that the actual height now is 56.67m on the highest side and 55.86m on the lowest side. The Width of walls at the base is 2.438 meters and the Weight of tower is approximately 14,500 tonnes. The construction was interrupted several times by wars, debt and while engineers worked on solutions to correct the lean. We now know that without these interruptions that allowed the soil to compress under the tower, it would have certainly toppled over. It is now stabilized by cables.

Thanks to the soft ground, it had begun to lean by the time its builders got to the third story, in 1178. Shifting soil had destabilized the tower’s foundations. Over the next 800 years, it became clear the 55-metre tower wasn’t just learning but was actually falling at a rate of one to two millimeters per year. Today, the Leaning Tower of Pisa is more than five meters off perpendicular.

San Francisco’s Millennium 58-Story Tower with Condominiums selling as high as $10 million is also sinking unevenly.

The Millennium Tower, completed in 2009, which its developers say is the largest reinforced concrete building in the western United States, has now sunk about 16 inches and is leaning six inches toward a neighboring skyscraper. The building’s tilt has become a public scandal, a dispute that has produced a wide-eyed examination of whether or not San Francisco’s frenetic skyscraper-building spree was properly monitored by city authorities. In a city bracketed by two major earthquake fault lines, the possibility of engineering flaws generates particular unease. The building spree in San Francisco has taken place for the most part in an area that used to be part of San Francisco Bay, land created using dredged soil as well as piles of detritus from the 1906 earthquake.

Unlike some downtown high-rises, the Millennium isn’t steel-framed. Instead, the developer chose a concrete design more common to residential buildings. It relies on huge columns, shear walls and beams, and it’s much heavier than steel. What’s more, the building is located on unstable mud-fill, just off the bay’s original shoreline. Unbelievably, only two of the numerous sky scrapers in San Francisco are resting on piles down to bedrock. But then most of the skyscrapers aren’t located off the original shoreline on mud-fill.

The problem is complicated on a huge hole that was dug next door starting in 2010 for the still-under-construction Transbay Transit Center bus and rail terminal. That project is run by the Transbay Joint Powers Authority, which consists of San Francisco, AC Transit, Caltrans and the operators of Caltrans — meaning that if Millennium Partners’ assessment is correct, those taxpayer-funded government entities could be on the hook for tens of millions in repairs. However, the transit bay authority did spend $58 million to shore up the building before starting the big dig.

The Millennium’s engineers anchored the building over a thick concrete slab with piles driven roughly 80 feet into dense sand. “To cut costs, Millennium did not drill piles to bedrock,” or 200 feet down, the transit center authority said in its statement. Had it done so, the agency said, “the tower would not be tilting today.” . . .

Apparently, many are not worried since sales are still occurring, sometimes a million or so less for each condo than the original price. However, looking at the number of lawsuits, the lawyers may make more than the cost of the skyscraper. . .

One condo owner suggested that the developers should lop off the top 20 floors to prevent the building from toppling over. . . .

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