The Rebuilding of Ground Zero, Part 136

While construction is proceeding on the Freedom Tower and is now surpassing 7 WTC as the tallest of the buildings at Ground Zero (on its way to the ultimate height of 1,776 feet), it seems that there's a problem with the design element for the tower's base.

The Freedom Tower as seen from Liberty Street

The glass cladding, which was supposed to be able to absorb explosions and break apart into tiny bits, isn't acting as designed or planned. Instead, tests reveal that blast damaged glass turns into large shards that can cause grievous injuries. This means that the prismatic glass element will be scrapped in favor of another option.

The plan was to drape the base with 2,000 clear prismatic glass panels and welded aluminum screens to create, in the words of the architect, “a dynamic, shimmering glass surface.”

But the glass has proved difficult to manufacture at that scale. In trials, the refinishing required for the prismatic effect has left the glass brittle and prone to shatter. With the steel frame of the building now rising to the 65th floor, the Port Authority of New York and New Jersey has scrapped the idea and sent the architects back for yet another revision.

“As design moved to the testing phase, it became clear that the prismatic glass simply had too many technical problems to overcome and at a budget that was not cost effective,” said John Kelly, a spokesman for the Port Authority. “We have been finalizing a design that will be far more practical while being both distinctive and magnificent.”

About $10 million had already been spent on the glass. David M. Childs of Skidmore, Owings & Merrill, who designed the tower and the prismatic glass covering, did not respond to phone calls seeking comment.

Douglas Durst of the Durst Organization, which owns a 10 percent stake in the building and is in charge of leasing it, said the switch in plans should have no effect on the timetable for the building, scheduled to open in January 2014. The new facade is likely to be made of more traditional clear glass panels, possibly with granite elements to tie it into the surrounding plazas.

The problem with the glass illustrates the tension inherent in the entire $3.2 billion project: how to create a skyscraper that is at once iconic and defended against terrorism, while also containing costs.

Some of the issues arose in the manufacturing process, where the glass was tempered, treated, and processed to create the prismatic look. The problem is that all the manufacturing processes done created a brittle glass that broke into shards rather than bits.

Meanwhile, new safety precautions have been put in place at 4WTC (HT: Curbed NY), where a metal bar fell through safety netting and hit a 10 year old pedestrian on Liberty Street causing minor injuries.

Local residents and businesses have also suggested construction of sidewalk sheds to further protect pedestrians and those working in the area from falling debris (I'm among those who regularly walk in that area). It definitely makes sense to improve safety procedures to prevent further safety incidents such as this.