cordon off

イギリス，ロンドンのthe Leadenhall Building（通称the Cheesegrater skyscraper）のボルトが破損しており，これで破損したボルトは合計で3つとなりました。
cordonは「〈道路地域など〉に非常線を張る」という意味の動詞（『プログレッシブ英和中辞典』小学館）。ここでは「歩行者の立ち入りを禁止していた」と解釈できます。
ちなみに『研究社 新英和中辞典』（研究社）によれば，このcordonの由来はイタリア語の「飾りひも」のようです。（Koyamamoto）

Third steel bolt breaks on Cheesegrater skyscraper
British Land says cause for broken bolts is 'hydrogen embrittlement'
British Land has revealed that another steel bolt on the Cheesegrater skyscraper has broken, bringing the total to three.
The real estate group said the third broken bolt was caught by "precautionary tethering" put in place on the building in the City of London last year.
It did not disclose when the bolt fractured, saying only that the incident occurred "recently".
In November, two steel bolts broke on the 737ft skyscraper just days apart, with one plummeting to the ground at the side of the building.
Nobody was hurt since it landed in an area that was already cordoned off for construction. But the bolts are roughly the size of a human arm and the 47-storey landmark was cordoned off from pedestrians while the incident was investigated.
http://www.telegraph.co.uk/finance/newsbysector/constructionandproperty/11344111/Third-steel-bolt-breaks-on-Cheesegrater-skyscraper.html