The undulating exterior of the future Transbay Transit Center will likely not be the originally planned glass because of safety concerns, but officials say a metal skin could contain a math- or science-based pattern that would make it educational for visitors.
Construction of the new transit hub on Mission Street between First and Fremont streets began in 2010, and several key steps have followed, including assessments for risk and vulnerability using federal guidelines. After the second such assessment that concluded in late 2011, it was found that any glass used on the outside of the structure would have to be significantly strengthened to meet those guidelines, which include blast safety in explosions.
The additional cost would have been $7.5 million, according to Transbay Joint Powers Authority documents.
Instead of the glass, authority officials will ask the project’s board of directors today to approve studying the use of a perforated metal material. If approved, it could end up saving about $17.5 million on materials and the awning’s construction.
“Yes, we could have kept glass,” said authority Executive Director Maria Ayerdi-Kaplan, “but it would have been expensive.”
Ayerdi-Kaplan said the metal panels would not appear heavy and dense, and much like the glass panels there would be a certain amount of transparency to them that would allow the substructure to be visible and for planned lighting schemes to remain.”
“So in the evening,” Ayerdi-Kaplan said of the backlighting plan, “the whole facility will be illuminated.”
Another part of the exterior plan is to try to use a pattern that is either mathematically or scientifically derived, Ayerdi-Kaplan said. One idea is a Penrose tiling, in which the small parts of a pattern repeat in the larger portions based on mathematical equations.
The patterned metal could be a teaching tool for visitors.
“We are really excited about the educational opportunities,” Ayerdi-Kaplan said.
Changing the material on the outside of the transit hub also could save money on long-term maintenance costs, according to authority spokesman Adam Alberti. Using rounded edges on the metal panels could help prevent dirt buildup, which would reduce cleaning needs, he said.
The authority’s board of directors is scheduled to consider today whether to approve letting the architect on the project, Pelli Clarke Pelli, to move ahead with design of a metal exterior.