Post on 16-Dec-2015
transcript
ENGR/PHIL 482Engineering & Ethics
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Instructorso Dr. Ray James, P.E. (Civil
Engineering)o 140 CE—845-7436o r-james@tamu.edu
o Dr. Charles E. (Ed) Harris, Jr. (Philosophy)o Bolton Hall—845-5697o e-harris@tamu.edu
William LeMessurier and the CitiCorp Center
A case study in engineering and ethics.
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Backgroundo William LeMessurier was the structural
engineer in responsible charge of the 1977 Citicorp building
o Site constraint--historic St. Peter’s Lutheran Church obstructed part of the site
o Innovative design solution used “air rights” above the church, built a new church
o Required unusual first floor column layout
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Citicorp Center Statistics
o Located in New York Cityo 59 stories, 915 ft, steel skeletono Engineer: William LeMessurier and Assoc.o First tall building to include a tuned-mass
damper to improve serviceability under wind loading
o Completed 1977 at a cost of $175 million
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LeMessurier’s innovative column
layout
Conventional column layout
Innovative column layout
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Citicorp building site challenge...
© Norman McGrath
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Design of the structure
To employ the innovative
column layout, LeMessurier developed a
series of diagonal braces
to transfer the upper floor
loads to the four columns.
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Design of the steel structure
Then he performed an otherwise conventional
structural analysis. To analyze wind loads, he
adopted the usual simplifying assumption
that the critical wind direction was
perpendicular to the widest side of the building.
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Design of the steel structure,
cont’d...
An innovative tuned mass
damper system was designed to reduce building sway in design
winds.
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Completion, 1977
The Citicorp Center building was
completed in 1977.
In 1978, LeMessurier got a telephone call from an engineering
student...
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A new, and serious question is raised...
o Stimulated by the student’s question, LeMessurier initiated additional analyses which led him to discover that, because of the unusual column layout, the critical wind direction was not what he had assumed, but rather, a direction diagonal to the building.
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Analysis for diagonal winds...
o His calculations indicated that there would be more wind load in the diagonal members than he had anticipated, so he reviewed their design.
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Review of structural capacities...
o LeMessurier had previously learned that a change order during construction had resulted in the substitution of (weaker) bolted connections in the diagonal members rather than the called-for welded connections.
o At the time, the bolted connections appeared to have adequate capacity, so his staff approved the change order.
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His disturbing conclusions:
o The structural analysis error (incorrect critical wind direction assumption) coupled with the weaker bolted connections in the diagonal members meant that the diagonal members were overloaded by a design wind from a quartering direction.
o Basically, the Citicorp Center building could collapse in a moderate hurricane.
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So…..o You have just learned that your
prize project could, with reasonable likelihood, collapse with casualties in the thousands and losses in the billions.
o What do you do?
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What did LeMessurier do?
o Advised his architect client’s lawyer and client’s insurance company
o Advised Citicorp, the building ownero Advised the city authoritieso Installed back-up generators for the
tuned mass damperso Retained a team of meteorological
experts to determine the risk of damaging windstorms
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What did LeMessurier do, cont’d?
o Initiated a repair plan whereby the bolted diagonal splices would be reinforced with welded plates to increase their capacity
o Developed an emergency evacuation plan for the area within a 5-block radius of the structure, involving 2000 Red Cross volunteer workers
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What did LeMessurier do, cont’d?
o Created a cover story to provide for the press, to explain the night-time welding operations in progress as an upgrade to reflect a recent change in the NYC building codes.