Transcript ENGR/PHIL 482 Engineering & Ethics Instructors o Dr. Ray James, P.E. (Civil Engineering) o 140 CE—845-7436 o [email protected] o Dr.

ENGR/PHIL 482
Engineering & Ethics
Instructors
o Dr. Ray James, P.E. (Civil Engineering)
o 140 CE—845-7436
o [email protected]
o Dr. Charles E. (Ed) Harris, Jr. (Philosophy)
o Bolton Hall—845-5697
o [email protected]
2 Sept 2002
LeMessurier and Citicorp Center
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William LeMessurier and the
CitiCorp Center
A case study in engineering and
ethics.
Background
o 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 City
o 59 stories, 915 ft, steel skeleton
o 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
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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
o
o
o
o
client’s insurance company
Advised Citicorp, the building owner
Advised the city authorities
Installed back-up generators for the tuned
mass dampers
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.
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