Part 3: The Discovery of the Change from Welds to Bolts
The Citicorp tower was constructed using LeMessurier's diagonal-bracing design, and work was finished in 1977. LeMessurier's innovation translated into a great weight savings; the tower was unusually light for its size. However, this meant that it would have a fair tendency to sway in the wind, so a tuned-mass damper was installed at the top of the building. The inertia of this 400-ton concrete block, which floated on pressurized oil bearings, worked to combat the tower's expected slight swaying. The Citicorp tower was the first structure ever to incorporate mechanical assistance to combat wind sway.
In May 1978, LeMessurier, acting as structural consultant to a new building being planned in
Pittsburgh, again thought of using a sort of diagonal brace as part of his design. As in the Citicorp tower, the braces were intended to be joined with full-penetration welds, but the process of welding, though it resulted in extremely strong joints, was expensive and time-consuming. A potential contractor for the Pittsburgh construction job pointed this out to LeMessurier, who immediately thought to counteract the contractor's fears with the success story of his Citicorp tower and its welded joints.
Unknown to LeMessurier, however, was that during the Citicorp tower's construction (the tower under construction is pictured on this page), the Citicorp contractors had decided, based on the cost of welding, to put the braces together using less expensive bolted joints. Though bolted joints were weaker than welded joints, the New York contractors had agreed that welds would be unnecessarily strong and that bolts would be sufficient for the job.
When LeMessurier referred the Pittsburgh contractor, concerned over the cost of welding, to the successful Citicorp job, he was told of the substitution of bolts for welds in the Citicorp project. LeMessurier did not consider the change to pose a safety hazard, however, since the substitution was rather reasonable from an engineering standpoint, and there wasn't any reason for LeMessurier, a distant consultant, to have been previously informed. This assessment would change over the next month, however, as LeMessurier would soon encounter new data indicating that the switch from welds to bolts compounded another danger with potentially catastrophic consequences.