Citicorp+Center

//Vanessa Rodriguez, BAE/MAE, Penn State, 2010 //
 * Citicorp Center ** - New York City (July 1978)

flat

=Introduction =

A fatal flaw was discovered only a year after the completion of the Citicorp building by the structural engineer himself, William J. LeMessurier (pronounced La Measure). The The fifty-nine story building could only withstand a sixteen-year-storm instead of the fifty-five-year storm it was designed for, every year there was a one in sixteen chance that the building would experience total collapse. It was the summer of 1978 and hurricane season was fast approaching, a severe storm could topple the building just a year after its completion. There were many contributors to the inadequate structural design of the Citicorp building, including changes made to the original design of the connections. William J. LeMessurier had three options, silence, suicide, or setting the events in to motion that would ensure the safety of thousands of building occupants in tandem with sacrificing his reputation and career. In July of 1978 LeMessurier mobilized an effort to repair all two-hundred joints of the steel-frame structure and employed subject matter experts to oversee the quality of welds, maintain the tuned-mass damper, provide weather forecasts three times a day, and monitor strain gauges on the building. Two-thousand Red Cross workers were also brought in to assist with the evacuation plan if needed. Two months later the repairs were complete making the Citicorp Building one of the most structurally sound in the world, able to withstand a seven-hundred-year storm. This secret retrofit valued at twelve-million dollars U.S. wasn't made public until almost twenty years after its completion and LeMessurier's reputation remained unscathed. (Morgenstern, 1995)

=Innovations= On its completion the Citicorp building was the seventh-tallest building in the world. The building site located on the east side of Lexington Avenue between Fifty-third and Fifty-fourth Streets shared the block with St. Peter's Lutheran Church. Citigroup wanted the whole block, and as part of the land acquisition negotiation Citigroup agreed to demolish and build a new church on site in exchange for the air-rights above the church. This meant that the Citicorp building was now allowed to horizontally project itself over the church. LeMessurier repositioned the columns so that they were located at half-way points under the exterior walls. The Citicorp building was raised up on 9-story stilts, with a 72 foot cantilever over the new church. (Morgenstern, 1995)

The base columns were made robust to handle the shear loads caused by wind forces and to provide a more aesthetically pleasing proportion; the columns were much larger than structurally necessary.It occurred to LeMessurier to make efficient use of these columns and run them up the length of the building therefore using them as a direct load path to the building's foundation. To direct the forces to the columns LeMessurier designed diagonal braces that carried the member forces to the center of each exterior wall; where the main column was located. (AR, 1976)

Another issue had to be addressed by the engineer; for a building of its height Citicorp was relatively lightweight making it more dynamically excitable. Several methods were considered to address the excessive deflections that would be caused by wind forces; they included increasing the stiffness of the building and semi-isolating the building from the ground by anchoring it on flexible moorings, but were deemed unfeasible. Le Messurier felt that the best option was to use a Tuned-Mass-Damper (TMD), a tuned- counterweight of 400 tons. This made the Citicorp building the first building to have mechanical aid as part of its structural design. (Gannon, 1985)

=Structural Design of Citicorp = At the time the Citicorp building was designed, the New York Building Code only considered the effects of diagonal winds on tall structures because this type of loading was critical for the traditional column layout; columns on each of the four corners. Until adoption of a new code in 1968, New York had required that all structures be designed "to resist, in the structural frame, horizontal wind pressure from any direction." In the early 1970s the prevailing standard of care was to design tall structures considering the effects of quartering winds .Tall steel frame buildings had been around for over half a century by the 1970s and the technology of making rigid connections with steel members was fully developed. (Kremer, 2002)

The steel-frame structure was comprised of a system of stacked load-bearing braces (V pattern) which redirected loads to the center and down the four columns the extended up the entire length of the building. These 48 braces are arranged in a six-tiered pattern on each side of the building and pick up the loads of gravity in increments and guide it down the column by diagonal in compression. These braces span 8 stories in height and were very conservatively designed to be erected in pieces joined by full penetration welds. These braces were also cantilevered seventy-two feet from each corner to support the edges of the tower floors. The central service core supporting the tower was comprised of four-massive 114 foot (35 meters) high columns. (ASCE, 2007)

= = During the 1970s, the building was considered lightweight in comparison to buildings of similar size. Building deflections were a structural concern and therefore wind tunnel testing was performed on the structure by one of the world's leading wind-tunnel-testing facilities of its time. The area modeled in detail was 4000 feet in diameter; roughly four city blocks in each direction. With the TMD included in the model the building achieved a 4% damping mechanically, this was meant to reduce the building's movement due to wind by as much as 50%. Located 59 stories above the sidewalk, the damper room was an enormous 80 feet by 80 feet. Dominating the center of the room was a concrete block twenty-nine feet squared and eight feet thick floated on preassurized oil bearings. The TMD cost was $1.5 million, less than 1% of the total building cost. This computer- controlled damper starts working when the outside wind velocity reaches about 25 mph or when the building sensors (accelerometers) detect a sway larger than 3 milli g's (three thousandths of the acceleration of gravity). When this happens, a 50-horsepower oil pumps thumps into action, and slowly the block begins to rise. For minutes later, the block has lifted 3/4 inch. Now it's standing on 12 hydraulic footpads the size of manhole covers, each separated from the 30-square-foot polished steel floor beneath the block by a near-frictionless layer of oil. The block's movement is inhibited by two sets of pneumatic gas springs designed by Neil Pattersen. The springs are made of pistons that could go +/- 3 1/2 feet and with a force of 150 kips to work in both directions. The block and stiffness of the springs have been tuned to the natural oscillation period of the building, 6.7 seconds. The block moves 90 degrees out of phase, to absorb the energy of the swaying structure, this out-of-phase movement damps the building sway. The damper produces an improvement, estimates LeMessurier, equivalent to quadrupling the building's structural bracing. That's a saving of nearly $4 million. (Gannon, 1985)

=The Failure = While working on a new building design in the spring of 1978, LeMessurier planned once to again implement diagonals. During a meeting with the steel fabricator the question came up on the connections of these diagonals; field welded full-penetration welds are expensive. LeMessurier called his associate to confirm the success on the field-welded connections used on the Citicorp building and was told that the welded connections were replaced by bolted connections designed by Bethleham Steel for a savings to the bank of $250,000. This was common practice for steel erectors at the time and the new joint design was based on the loads provided by LeMessuriers' Cambridge office. There is a discrepancy in the account of events, whether or not LeMessurier was aware of the change from bolts to welds. McNamara claims LeMessurier knew of the switch to bolts, this statement has some credibility since LeMessurier's Cambridge office was the one that provided the design forces to Bethlehem Steel.

In June of 1978 LeMessurier received a call from an architectural student from New Jersey who was assigned the Citicorp building as a project. The student told LeMessurier that his professor says columns should always be put on the building corners.LeMessurier explained the site restrictions of the project and told the student that due to the building's innovative column layout, it was particularly resistant to quartering or diagonal winds. After hanging up he gave this final statement some thought and chose to further investigate. In conventional buildings; columns on the four corners, the worst loading case is when the wind is pushing straight on the building. Upon investigating he discovered that the worst loading case on the Citicorp building was not when the wind is perpendicular but when the wind is on the diagonal. LeMessurier calculated the forces in the diagonals by method of virtual work and determined that with diagonal wind the stresses on half the diagonals vanish and double on the other half, a "very peculiar behavior." (LeMessurier, 1995)

This critical design flaw may not have been as crucial if the original full-penetration welds had been used but since the New York design firm ignored quartering winds when choosing bolts over welds for the connections, these connections were now undersized. By going through the shop drawings, LeMessurier also noticed that the New York contractors exempted many diagonal braces from load-bearing calculations by interpreting the building code in a certain way. LeMessurier's firm used New York City's truss safety factor of 1:1 instead of the column safety factor of 1:2. The code states that since columns in tall buildings are put in tension from wind when bldg is leading over, you should only subtract from the tension of the wind 3/4 of the dead load. The engineers said that the diagonals aren't like a column in a bldg, but instead, more like a diagonal of a truss therefore you can subtract the full dead load. What this did was reduced the required number of bolts by one-half. Each bolt was good for 100 kips load, this meant that with the assumptions made by the engineer, each connection needed a total of four bolts instead of eight bolts. The original design connection consists of high strength, 1 1/4 to 1 1/2 in. bolts, through the holes. (ENR, 1978)


 * = (2000k tension wind) - (1600k dead load) = 400k ||= vs. ||= (2000k tension wind) - [3/4(1600k dead load)]=800k ||
 * = bolts good for 100k each... 4 bolts ||=  ||= bolts good for 100k each... 8 bolts ||

Too few bolts used in the first place without even considering diagonal winds. According to LeMessurier's calculations, diagonal winds increase member load by 40%. Le Messurier reran the tunnel tests to include quartering winds and bolts, the quartering winds were calculated to be 70mph ( 113 km/h). He discovered a 60% increase in member stress was possible when he checked the max force in any diagonals in the building in 100 years, the members could vibrate synchronously during a storm. A 40% increase in member stress meant a 160% increase of the stress on the building joints. He also discovered that if a storm pulled a joint apart on the 13th floor, the whole building would collapse. Also if the storm causes the power to go out, the damper would not work. The design was for 55 year wind speed with the damper and 16 year design if the damper didn't work. In other words, there was a one in sixteen chance every year that the building will collapse.

In a video recording of LeMessurier's account of the 59 Story Crisis, he states "Have you done everything as well as your peers have done? Nobody and his brother would ever look at the diagonal winds, that is just not in the mindset." This statement is contested by two senior members of LeMessurier's firm who claim that it was common to check diagonal winds when designing tall buildings. There is debate as to whether the structure was at all checked for quartering winds during the design phase. LeMeassurier claims that he did not because the code did not demand it. However, Robert J. McNamara, the managing principal for Citicorp in LeMessurier Associates' Cambridge office at the time, states that LeMesssurier did in fact check the effects of quartering winds and deemed that they did not govern the design and need not be furthered considered. This suggests that LeMessurier may have used the code as a shield from fully accepting fault on the flawed design of the wind resisting system.

=Mobilization Efforts to Repair Citicorp = LeMessurier asked himself " How would i fix it?" and then he realized that these diagonals were set back and the connections were made above the floor line making them quite accessible. He decided to to remedy the connections by applying heavy steel-welded band-aids on each side of the joint to build up the strength of the joint. The new welded plates, typically 1 1/2 in. thick and weighing 200 to 300 pounds, were shaped like thick elongated Hs. There was never any question on the strength of the diagonal members themselves. Plywood houses were set up to shield the building occupants from the welding and debris. The work was done at night when staff would not be occupying the building.

Leslie E. Robertson was brought in and became the bank's consultant on this matter. He felt that the seriousness of the matter was more imminent than LeMessurier believed. He refused to solely rely on the dampers, emergency generators were put-in-place in the event that a storm would knock out the power and hinder the tuned-mass-damper useless. Three Meteorological experts were retained to provide updates three times throughout a day. An emergency evacuation plan was developed in conjunction with local law enforcement, search and rescue, firefighters, major city authority figures, and shelters. 2000 emergency red cross workers were kept on stand-by in the event of a failure. <span style="font-family: Arial,Helvetica,sans-serif;">With the data collected from the new wind tunnel tests, LeMessurier was able to constantly calculate which joint to weld on a particular day to be ahead of the game on the return period. (LeMessurier, 1995)

The Structural work amounted to $8 million, the fees by Citicorp were an additional $4 million. Le Messurier was able convince them to settle for $2 million which was the maximum amount his insurance would allow for. LeMessurier's reputation was elevated due to his ethical approach to an unsavory situation and considered a hero by his peers. This case study was and still is used to represent an engineer with outstanding moral fiber. His actions taught engineers a valuable lesson in the responsibility over the lives of others in the design of structures. His secretary was even able to convince his liability insurer to lower his premium.Due to the city-wide press strike at the time, the extent of the danger was unknown to the public for the better part of two decades. (Morgenstern, 1995)

=<span style="font-family: Arial,Helvetica,sans-serif;">Ethical Discussion = <span style="font-family: Arial,Helvetica,sans-serif;">Throughout my research I found many inc onsistencies with statements made between LeMessurier and his peers. LeMessurier in his public account of the events kept very close to the story published by Joe Morgenstein in the New Yorker. Major discrepancies include whether or not he knew of the change from welds to bolts, if he ever considered quartering winds, and if it was the standard of practice to check for diagonal winds. Many ethical issues arise in this case study, whether or not lying to the public is acceptable or if it was just an attempt to preserve his reputation.(Korman, 1995)

The seriousness of the problem were kept from the public; according to LeMessurier, in order to avoid scaring the public. Misleading reports were fed to the press about the reasons for the retrofit, "LeMessurier maintain that the...tower has well over the structural support it requires to withstand anticipated wind loads and the purpose of the extra bracing is simply to supplement it." Canon 3 of the National Society of Professional Engineers Code of Ethics states that engineers shall "Issue public statements only in an objective and truthful manner." Whether his choice to keep this retrofit a secret for almost two decades was self-serving or a public service is a source of much debate. The National Society of Professional Engineers (NSPE) Board of Ethical Review (BER) concluded that while "the desire to avoid public panic is certainly a legitimate factor in deciding on a course of action...withholding critical information from thousands of individuals whose safety in compromised over a significant period of time is not a valid alternative..." (<span style="font-family: Arial,Helvetica,sans-serif;">Kremer, 2002)

Citicorp building is such a fascinating structure due to the many innovations implemented such as the diagonals, column layout, and the TMD. When stepping out of the normal realm of design an engineer must proceed with caution and avoid assumptions based on conventional design theories. It was LeMessurier's obligation as a responsible engineer to check all possible wind directions regardless of the New York Building Code; the code provides an engineer with the absolute minimum standards. It was also irresponsible to rely so heavily on the tunes-mass-damper to reduce sway during a storm due to the high probability of an electrical knock-out. It is best to use tried and true methods in the field of building construction and to proceed with caution otherwise. (<span style="font-family: Arial,Helvetica,sans-serif;">Kremer, 2002)

Regardless of whether or not LeMessurier was aware of the change from bolts to welds is inconsequential because the connections were designed to withstand the incorrect forces provided by LeMessurier's firm, and therefore he is responsible. The forces of the connections were determined based on the perpendicular wind he assumed would control the structural design. His claim that he was not aware of the change does not speak highly of the lines of communication between the engineer and contractor.

In today's society does it really pay to tell the truth? The average engineer does not have the popularity and esteem achieved by LeMessurier during his career. Today if an engineer were to come forward about a mistake he/she committed, there would likely be an unsavory outcome. The engineer would be identified as less than perfect and may lose their job and credibility. And most likely, it would be the engineer who would have to pay the retrofit of the structure. Today's society needs to still work on creating a more forgiving atmosphere that promote openness about building failures. (Morgan, 1996) Engineers have a "responsibility to advance the knowledge and usefulness of the profession", this was ignored by LeMessurier for two decades, making it impossible for others to learn from his mistakes and to increase the understanding of the effects of quartering winds on unconventional column layouts. His defense, "I wasn't ready yet" is dissatisfying. (<span style="font-family: Arial,Helvetica,sans-serif;">Kremer, 2002)

Were Le Messurier's actions ethical? There is no clear-cut answer. As engineers we are trusted to use our judgment in solving problems, so the answer depends on whether or not you feel LeMessurier abused that trust.

=<span style="font-family: Arial,Helvetica,sans-serif;">Bibliography =

<span style="font-family: Arial,Helvetica,sans-serif;">Bellows, Alan (April 12, 2006), "A Potentially Disastrous Design Error." Damn Interesting < <span style="color: #0000ff; font-family: Arial,Helvetica,sans-serif;">[] <span style="font-family: Arial,Helvetica,sans-serif;">> <span style="color: #808080; font-family: Arial,Helvetica,sans-serif;">Article questioning whether the engineers of today are capable of making the correct ethical decision such as that made by LeMessurier.

<span style="font-family: Arial,Helvetica,sans-serif;">Bierut, Michael (April 06, 2006), "When Design is a Matter of Life or Death." The Design Observer Group <http://www.designobserver.com/observatory/entry.html?entry=4197> <span style="color: #808080; font-family: Arial,Helvetica,sans-serif;">Article questions whether industry has evolved in moral character.

<span style="font-family: Arial,Helvetica,sans-serif;">Gannon, Robert (August 1985) "Buildings that Keep their Balance." Popular Science, (58-61) <span style="color: #808080; font-family: Arial,Helvetica,sans-serif;">A look into the innovative tuned-mass damper implemented in the Citicorp building.

<span style="font-family: Arial,Helvetica,sans-serif;">Horsley, Carter B., "The Midtown Book." The City Review <http://www.thecityreview.com/citicorp.html> <span style="color: #808080; font-family: Arial,Helvetica,sans-serif;">The Citicorp Building from an architectural perspective and its structural engineering feat.

<span style="font-family: Arial,Helvetica,sans-serif;">Korman, Richard (October 30, 1995), "LeMessurier's Confession." Engineering News Record (10) <span style="color: #808080; font-family: Arial,Helvetica,sans-serif;">This article criticizes LeMessurier's decision to keep the retrofit from the public.

<span style="font-family: Arial,Helvetica,sans-serif;">Korman, Richard (November 20, 1995), "Critics grade Citicorp Confession." Engineering News Record (10) <span style="color: #808080; font-family: Arial,Helvetica,sans-serif;">This article criticizes LeMessurier's claim that he takes responsibility for others mistakes.

<span style="font-family: Arial,Helvetica,sans-serif;">Kremer, Eugene, "(Re) Examining the Citicorp Case: ethical paragon or chimera?" Architectural Research Quaterly, 2002, v.6, n.3, (269-276) <[]> <span style="color: #808080; font-family: Arial,Helvetica,sans-serif;">The report of the Citicorp tower's structural inadequacy and the effort leading to its repair engendered widespread praise for all involved.

<span style="font-family: Arial,Helvetica,sans-serif;">LeMessurier, William J. (November 17, 1995) The 59 story crisis [videorecording] : a lesson in professional behavior <span style="color: #808080; font-family: Arial,Helvetica,sans-serif;">William LeMessurier, one of the nation's most distinguished structural engineers, discusses ethical dilemmas he faced with structural deficiencies in the design of the Citicorp headquarters.

<span style="font-family: Arial,Helvetica,sans-serif;">Morgan, J.A. (December 1996), "Engineers on the Line." Civil Engineering (27) <span style="color: #808080; font-family: Arial,Helvetica,sans-serif;">This article addresses the difficulties of coming forward with information in today's society.

<span style="font-family: Arial,Helvetica,sans-serif;">Morgenstern, Joe (May 29, 1995)."The Fifty-Nine-Story Crisis." The New Yorker, (45-53) <[]> <span style="color: #808080; font-family: Arial,Helvetica,sans-serif;">The first time the secret of Citicorp was revealed to the public in a very detailed article in The New Yorker.

<span style="font-family: Arial,Helvetica,sans-serif;">Online Ethics Center for Engineering (June 23, 2006), "William LeMessurier- The Fifty-Nine-Story Crisis: A Lesson in Professional Behavior" National Academy of Engineering, <[]> <span style="color: #808080; font-family: Arial,Helvetica,sans-serif;">A detailed account of the problems faced by LeMessurier.

<span style="font-family: Arial,Helvetica,sans-serif;">PBS's "Building Big" Series <http://www.pbs.org/wgbh/buildingbig/wonder/structure/citicorp.html> <span style="color: #808080; font-family: Arial,Helvetica,sans-serif;">Provides quantitative facts and comparisons in describing the Citicorp crisis.

<span style="font-family: Arial,Helvetica,sans-serif;">Ratay,Robert T. (2010). "Citicorp Building New York" Forensic Structural Engineering Handbook <span style="color: #808080; font-family: Arial,Helvetica,sans-serif;">This chapter in the book deals with ethics in engineering, particularly Le Messurier's Citicorp Center.

<span style="font-family: Arial,Helvetica,sans-serif;">Rosen, Stephanie (September 1993), "Breaking Barriers." Modern Steel Construction v.33, no.9, (26-35) <http://www.modernsteel.com/issue.php?date=September_1993> <span style="color: #808080; font-family: Arial,Helvetica,sans-serif;">This article goes into detail about the innovations employed by LeMessurier in many of his buildings, including Citicorp.

<span style="font-family: Arial,Helvetica,sans-serif;">Science Hack, "The Secret Retrofit of the Citibank Tower in 1978" [videorecording] <[]> <span style="color: #808080; font-family: Arial,Helvetica,sans-serif;">A video telling the secret story of the repairs made on the Citicorp Building due to high winds at the building corners.

<span style="font-family: Arial,Helvetica,sans-serif;">Unknown Author (July 2007), "A Question of Ethics." ASCE v.32, no.7, (10) <http://www.asce.org/contextual.aspx?id=16703> <span style="color: #808080; font-family: Arial,Helvetica,sans-serif;">This article goes into detail about the structural design of Citicorp.

<span style="font-family: Arial,Helvetica,sans-serif;">Unknown Author (August 17, 1978), "Engineers afterthought sets welders to work bracing tower." Engineering News Record (11) <span style="color: #808080; font-family: Arial,Helvetica,sans-serif;">This article explains the retrofit and the supposed reason for implementing them.

<span style="font-family: Arial,Helvetica,sans-serif;">Unknown Author (Mid-August 1976), Architectural Record (66-71) <span style="color: #808080; font-family: Arial,Helvetica,sans-serif;">This article details the structural design of the Citicorp Building.

<span style="font-family: Arial,Helvetica,sans-serif;">Womak, Larry (Spring 1996), "A Point of View: The New- and Unimproved?-Corporate Integrity" National Productivity Review <span style="color: #808080; font-family: Arial,Helvetica,sans-serif;">This article points out how corporate America has lost all it's dignity and cannot be taken at its word. It compares case studies to that of the Citicorp failure and how it was handled.

=<span style="font-family: Arial,Helvetica,sans-serif;">Additional References =

<span style="font-family: Arial,Helvetica,sans-serif;">LeMessurier, William J. (April 19, 2000), "Blowing the Whistle on Yourself." North Carolina State University, Dept. of Civil Engineering 2000, (28)

<span style="font-family: Arial,Helvetica,sans-serif;">LeMessurier, William J. (April 19, 2000), "Wind Resistant Design" <span style="color: #808080; font-family: Arial,Helvetica,sans-serif;">Article provided by WIlliam LeMessurier focusing on aerodynamics and structural design.

<span style="font-family: Arial,Helvetica,sans-serif;">Goldstein, Stanley H. (October 1996), "Engineering Ethics.", Civil Engineering, v.66, n.10, (40-44)

<span style="font-family: Arial,Helvetica,sans-serif;">Mehlman, Robert (May-June 1977), "Elevating the Urban Environment." Industrial Design, 1977 May-June, v.24, n.3, (42-48) <span style="color: #808080; font-family: Arial,Helvetica,sans-serif;">Citicorp Center, New York, N.Y.; Hugh Stubbins; Associates,archts.; William LeMessurier; Associates, mechanical and electrical engineers.

<span style="font-family: Arial,Helvetica,sans-serif;">Rastorfer, Darl (February 1985), "William J. LeMessurier's super-tall structures: architecture-engineering." Architectural Record, 1985 Feb., v.173, no.2, (150-157) <span style="color: #808080; font-family: Arial,Helvetica,sans-serif;">A view into five projects including Erewhon Center; Federal Reserve Bank of New York, New York; Citicorp Center, New York; Singapore Treasury Building, Singapore; 383 Madison Avenue, New York.

<span style="font-family: Arial,Helvetica,sans-serif;">Rastorfer, Darl (February 1985), "William J. LeMessurier's super-tall structures: A search for the ideal." Architectural Record, 1985 Feb., v.173, no.1, (141-151) <span style="color: #808080; font-family: Arial,Helvetica,sans-serif;">Includes projects for Bank of the Southwest, Houston and InterFirst Plaza of the Dallas Main Center, Dallas; also substantial discussion on shear stress.