Keynote: The Building Built on Stilts
summary
A Citibank tower is cantilevered over St. Peter’s Church via a novel diagonal-brace skeleton built after the first air rights deal in NYC; the structure uses a 410-ton tuned mass damper and a lightweight 25,000-ton steel frame. An engineer discovers the diagonals take ~40% higher load under quartering winds and that joints were bolted, not welded, creating catastrophic collapse risk in a ~1-in-16‑year tropical-storm scenario. The remedy is secret overnight welding of two-inch steel mending plates plus backup generators and an evacuation plan, and the building survives.
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