---
title: "Citicorp Center engineering crisis"
chunk: 2/4
source: "https://en.wikipedia.org/wiki/Citicorp_Center_engineering_crisis"
category: "reference"
tags: "science, encyclopedia"
date_saved: "2026-05-05T04:22:37.754740+00:00"
instance: "kb-cron"
---

== Discovery ==
In May 1978, after the building structure was completed, LeMessurier was designing a similar building with wind braces in Pittsburgh, and a potential contractor questioned the expense of using welded rather than bolted joints. LeMessurier asked his office how the welds went at the Citicorp construction and was then told that bolts had been substituted for the welded joints he had prescribed.
In June 1978, Princeton University engineering student Diane Hartley was writing her senior thesis about Citicorp Center's design at the suggestion of her professor, David Billington. As part of that work she analyzed the structural design and calculated stresses from quartering winds, finding them higher than the maximum expected stress values provided to her by LeMessurier's firm. Hartley asked her contact at the building design company, Joel S. Weinstein, a junior member of its staff, about the issue, and he provided her with a copy of the firm's calculations for perpendicular winds (but not for quartering winds). Only Weinstein was indicated as signing off on the copies of the calculations he provided to her, although she expected to see them initialed by a second person to confirm them, as was the usual practice in the industry. According to Hartley, she asked for calculations about quartering winds, and Weinstein said he would provide them but then didn't. Calculations for quartering winds were not required by the building code at the time, and were not common practice in the industry (although the design of the building was obviously unusual and would have justified special analysis). Weinstein assured her that the building could handle the necessary forces, and she did not further pursue the issue beyond writing about it in her thesis, which recorded her concerns and the response she received. In his feedback on Hartley's thesis, Billington questioned why her calculations weren't checked against figures from the firm.
In June 1978, LeMessurier was answering questions via phone with a young architectural student, self-identified more than 40 years later as Lee DeCarolis. On July 24, 1978, LeMessurier went to his office and conducted calculations on Citicorp Center's design. He had thought that perpendicular winds were the critical case for the building rather than quartering winds. He found that, for four of the eight tiers of chevrons, quartering winds would create a 40 percent increase in wind loads and a 160 percent increase in the load at the bolted joints. Citicorp Center's use of bolted joints and the loads from quartering winds would not have caused concern if these issues had been isolated. However, the combination of the two findings prompted LeMessurier to run tests on structural safety. He concluded that the original welded-joint design could withstand the load from both straight-on and quartering winds, but the modified bolted-joint design could be vulnerable to a 70-mile-per-hour (110 km/h) near-hurricane-force quartering wind. LeMessurier also discovered that his firm had used New York City's truss safety factor of 1:1 instead of the column safety factor of 1:2.
On July 26, LeMessurier visited wind-tunnel expert Alan Garnett Davenport at the University of Western Ontario. Davenport's team conducted calculations on the building and concluded not only that LeMessurier's modeling was correct but also that, in a real-world situation, member stresses could increase by more than the 40 percent LeMessurier had calculated.  LeMessurier then went to his Maine summer home on July 28 to analyze the issue.  With the tuned mass damper active, LeMessurier estimated that a wind capable of toppling the building had a one in fifty-five chance of happening any year. But if the tuned mass damper could not function due to a power outage, a wind strong enough to cause the building's collapse had one in sixteen chance of happening any year.