Steel in the News
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Posted by Keith Grubb on May 9, 2008 at 3:55 PM.
In the case of one 11-year-old Chicago office tower, “up” was the only way to go. Lohan Associates (now Goettsch Partners) designed the 33-story steel-framed Blue Cross-Blue Shield tower with vertical expansion in mind: columns had been stubbed through the roof, and a dramatic glass-enclosed atrium was designed to become high-rise elevator shafts. Now that Blue Cross has outgrown the tower, a 24-floor vertical expansion is underway.
Adding more floors to an existing structure is not without its challenges, especially when you’re starting from 500 feet in the air. For example, a 17-ton derrick was hauled up through the building in sections on a 6,000-lb-capacity freight elevator. The 17-ton derrick was used to bring up the pieces for a 35-ton derrick, which was then used to dismantle the 17-ton derrick and assemble the first of two tower cranes. The location of the building, just a few blocks from the lake Michigan shoreline, made winds an issue. City of Chicago rules prohibit crane assembly when winds are more than 30 mph, delaying tower crane erection by 30 days.
Read more about this carefully-planned steel project here.