Structural engineer Bill LeMessurier (pronounced LeMeasure) and architect Hugh Stubbins faced a challenge when they worked on

the plans for New Yorks fifth highest skyscraper. St. Peters Lutheran Church owned and occupied a corner of the lot designated in its

entirety as the site for the new structure. An agreement was reached: The bank tower would rise from ninestory-high stilts positioned

at the center of each side of the tower, and the church would be offered a brand new St. Peters standing freely underneath one of

the cantilevered corners. Completed in 1977, the Citicorp Center appears as shown in Figure 13. The new church building is seen

below the lower left corner of the raised tower.

LeMessuriers structure departed from the usual in that the massive stilts are not situated at the corners of the building, and half of

its gravity load as well all of its wind load is brought down an imaginatively designed trussed frame, which incorporates wind braces

on the outside of the tower.11 In addition, LeMessurier installed a tuned mass damper, the first of its kind in a tall building, to keep

the building from swaying in the wind.

Questions asked by an engineering student a year after the towers completion prompted LeMessurier to review certain structural

aspects of the tower and pose some questions of his own.12 For instance, could the structure withstand certain loads caused by strong

quartering winds? In such cases, two sides of the building receive the oblique force of the wind, and the resultant force is 40 percent

larger than when the wind hits only one face of the structure straight on. The only requirement stated in the building code specified

adequacy to withstand certain perpendicular wind loads, and that was the basis for the design of the wind braces. But there was no

need to worry because the braces as designed could handle such an excess load without difficulty, provided the welds were of the

expected high quality.

Nevertheless, the students questions prompted LeMessurier to place a call from his Cambridge, Massachusetts, office to his New York

office, to ask Stanley Goldstein, his engineer in charge of the tower erection, how the welded joints of the bracing structure had

worked out. How difficult was the job? How good was the workmanship? To his dismay, Goldstein answered, Oh, didnt you know?

[The joints] were never welded at all because Bethlehem Steel came to us and said they didnt think we needed to do it. The New

York office, as it was allowed to do, had approved the proposal that the joints be bolted instead. But again the diagonal winds had not

been taken into account.

At first, LeMessurier was not too concerned; after all, the tuned mass damper would still take care of the sway. So he turned to his

consultant on the behavior of high buildings in wind, Alan Davenport at the University of Western Ontario. On reviewing the results

of his earlier wind tunnel tests on a scaleddown Citicorp Center, Davenport reported that a diagonal wind load would exceed the

perpendicular wind load by much more than the 40 percent increase in stress predicted by an idealized mathematical model. Winds

sufficient to cause failure of certain critical bolted jointsand therefore of the buildingcould occur in New York every sixteen years.

Fortunately, those braces that required strengthening were accessible, but the job would be disruptive and expensive, exceeding the

insurance LeMessurier carried.

LeMessurier faced an ethical dilemma involving a conflict between his responsibilities to ensure the safety of his building for the sake

of people who use it, his responsibilities to various financial constituencies, and his self-interest, which might be served by remaining

silent. What to do? He retreated to his summerhouse on an island on Sebago Lake in Maine. There, in the quiet, he worked once more

through all the design and wind tunnel numbers. Suddenly he realized, with an almost giddy sense of power, that only he cou ld

prevent an eventual disaster by taking the initiative. Having made a decision, he acted quickly. He and Stubbins met with their insurers,

lawyers, the bank management, and the city building department to describe the problem. A retrofit plan was agreed on: The wind

braces would be strengthened at critical locations by welding two-inch-thick steel plates over each of more than 200 bolted joints.

Journalists, at first curious about the many lawyers converging on the various offices, disappeared when New Yorks major newspapers

were shut down by a strike. The lawyers sought the advice of Leslie Robertson, a structural engineer with experience in disaster

management. He alerted the mayors Office of Emergency Management and the Red Cross so the surroundings of the building could

be evacuated in case of a high wind alert. He also arranged for a network of strain gages to be attached to the structure at strategic

points. This instrumentation allowed actual strains experienced by the steel to be monitored at a remote location. LeMessurier insisted

on the installation of an emergency generator to assure uninterrupted availability of the damper. The retrofit and the tuned mass

damper had been readied to withstand as much as a 200-year storm.

The parties were able to settle out of court with Stubbins held blameless; LeMessurier and his joint-venture partners were charged

the $2 million his insurance agreed to pay. The total repair bill had amounted to more than $12.5 million. In acting responsibly,

LeMessurier saved lives and preserved his integrity, and his professional reputation was enhanced rather than tarnished by the

episode.