Re­view of cracked tower win­dow OKd

San Francisco Chronicle Late Edition - - BAY AREA - By Do­minic Fra­cassa

A Stan­ford Uni­ver­sity en­gi­neer­ing pro­fes­sor work­ing with San Fran­cisco’s De­part­ment of Build­ing In­spec­tion con­cluded there’s “no rea­son” to fur­ther in­ves­ti­gate what caused a win­dow to crack on the 36th floor of the Mil­len­nium Tower.

Pro­fes­sor Greg Deier­lein’s con­clu­sions were pre­sented in a let­ter that Build­ing In­spec­tion sent Thurs­day to the tower’s man­age­ment. The de­part­ment asked Deier­lein to re­view the find­ings of a foren­sic re­port on the cracked win­dow that found no ev­i­dence that the is­sue was linked to the build­ing’s on­go­ing sink­ing and tilt­ing. The re­port, con­ducted by the en­gi­neer­ing firm Al­lana Buick & Bers on be­half of the tower’s man­agers, blamed the crack on an “ex­te­rior im­pact,” but gave no in­di­ca­tion as to what might have struck the win­dow. Deier­lein found no rea­son to ques­tion the re­port’s find­ings. “While it’s fair to say DBI ac­cepts Pro­fes­sor Deier­lein’s find­ings per his re­view of the newly is­sued AB&B re­port, we un­der­stand that in or­der for (Mil­len­nium’s man­age­ment) to com­plete its in­ves­ti­ga­tion of the cracked glass” the win­dow would have to be re­moved and sub­jected to ad­di­tional anal­y­sis, De­part­ment of Build­ing In­spec­tion spokesman William Strawn said.

The crack was dis­cov­ered about 2:30 a.m. on Sept. 1 af­ter the home­owner in unit 36B awoke to a “mas­sive” bang­ing sound. “This sound was so mas­sive in scale, it sounded like a huge, thick vault door had just slammed shut,” the home­owner said, de­scrib­ing the event to the Al­lana en­gi­neer­ing firm. For the next 30 min­utes, the home­owner de­scribed hear­ing what sounded like the glass splin­ter­ing in the win­dow.

The cracked win­dow prompted wide­spread spec­u­la­tion about whether it was re­lated to the tower’s sink­ing and tilt­ing. Since it opened in 2009, Mil­len­nium Tower has sunk by around 18 inches and is tilt­ing to one side.

Over con­cern for pub­lic safety, Build­ing In­spec­tion or­dered the tower’s man­agers to tape up the win­dow and in­stall over­head scaf­fold­ing to pre­vent glass from fall­ing onto the Mis­sion and Fre­mont side­walks.

The tower’s man­agers in­di­cated they were pre­par­ing to re­move the scaf­fold­ing on the rec­om­men­da­tion of the en­gi­neer­ing firm’s re­port. But Build­ing In­spec­tion or­dered the scaf­fold­ing to be left in­tact un­til the win­dow is re­placed, which must be com­pleted by Nov. 18. The build­ing’s man­age­ment said last month the re­place­ment glass had to be or­dered from Shang­hai, so the re­place­ment would prob­a­bly take place in mid-Novem­ber.

The De­part­ment of Build­ing In­spec­tion also man­dated that the tower’s man­age­ment com­plete a “vis­ual in­spec­tion” of all sim­i­lar win­dows in the 416-unit tower by Dec. 21.

San Fran­cisco De­part­ment of Build­ing In­spec­tion

A crack in a win­dow at the Mil­len­nium Tower was caused by an “ex­te­rior im­pact,” en­gi­neers say.

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