To solve this, chief structural engineer William LeMessurier designed an absolute marvel.Instead of putting the building's massive support columns at the four corners, he moved them to the center of each of the four sides. This allowed the corners of the building to hang out mid-air, cantilevering right over the top of the church. To make this work safely, LeMessurier designed a skeleton of chevron-shaped (V-shaped) steel braces running up the outside of the tower to redirect the weight down through those center stilt The blueprints LeMessurier drew up were flawless. They specified that the massive joints connecting the chevron steel braces together had to be welded to handle the incredible loads. However, during construction in 1976, the steel fabricators (Bethlehem Steel) approached the contractor with a proposal to save money and time. They suggested replacing the heavy, labor-intensive welded joints with bolted joints. The contractor checked the math based on New York City building codes at the time. The codes only required engineers to calculate "perpendicular" winds—winds hitting the flat face of a building head-on. Under perpendicular winds, the bolts were technically strong enough. The substitution was approved, the money was saved, and the building opened in 1977 to massive acclaim. In 1978, a year after the building opened, an undergraduate engineering student named Diane Hartley was writing her thesis on the Citicorp Center. Her professor had doubted the stability of the center-stilt design. When she ran the math, she realized something didn't add up: if the wind hit the building at a 45-degree angle (diagonal "quartering winds"), it would hit two sides at once, creating a massive twisting force that doubled the load on the internal chevron braces. LeMessurier wasn't defensive; he decided to look into the math himself. He ran the numbers for diagonal winds against his original welded design, and it was perfectly safe. But then, he discovered the horrifying truth: the field office had substituted bolts for welds to save money. When he calculated 45-degree quartering winds against the bolted joints, the numbers were catastrophic. The bolts would shear. In a major storm—the kind of hurricane New York gets once every 16 years—the joints would fail, and the entire 59-story skyscraper would topple over into Midtown Manhattan, triggering a domino effect of destruction. To make matters worse, the building's tuned mass damper (a massive 400-ton concrete block on the roof meant to slow down swaying) relied on electricity. If a major storm knocked out power to the city, the building wouldn't even survive a 1-in-16-year stormit could collapse in a much more common event.