[Music]
the city cop center or 601 lexington
as it is known today had a major
structural defect
at the time of construction its story is
both fascinating with many twists and
turns
with an unlikely savior and a race
against time to rectify the building
before it collapses
it's also a tale of engineering ethics
as it was designed by a world-renowned
engineer
that had to realize his major mistake hi
i'm brendan
your structural engineer let's get into
it the city corp center at the time of
construction was to be the seventh
tallest building in the world
topping out at a height of 279 metres
and it required some of the best
engineers in the world to come together
under the lead of willie miller measure
this building also had a striking
feature at its base
you see they planned it they brought the
land but they didn't have rights over
the whole block there was a church
saint paul's luca and church on the side
as well they allowed them to demolish it
and rebuild a new church however they
still require the church to sit on the
corner underneath one of the corners of
this towering building
and they didn't allow any structure to
pass through either onto the building or
through their structure this
required them to come up with a unique
design solution they did instead of
having the columns in the corner like a
standard build
they move them to the center of each
base this is where we get the striking
feature of the citicorp tower to a
towering height of 35 meters and coming
to a
22 meter cantilever essentially
cantileving up and over
the building this is a unique feature of
the city corp tower it makes it quite
iconic for its area this feature
required some unique engineering
solutions to solve it
you see it had these massive cantilevers
so what they came up with
was essentially a dye grid system with
reverse chevrons going up the building
that allow the forces to strike
back to that central column to bring the
forces from the outer edges
back to the central column on the frame
these external frames were also designed
to help resist the wind loads
william was so impressed with the design
of this tower and one of the engineering
expressed on the outer face
showing its unique dye grid system
during many debates and discussions he
lost out to the architect he wanted his
big glass
tower and this is what we see today this
external diagram was not there
only just for the gravity forces for
transferring the loads from the outer
columns
i was also there for the stability
system this is one of the unique
features of the tower and also led to
one of the design floors
this design floor was not found out till
much later after this building was
occupied and it came for an
unlikely place due to the unique
features in this building
it was one of the recommended buildings
review when you're doing a design course
through university and this building was
assigned
to an undergraduate engineer diane
hartley so she took the building
and was reviewing it when she was
reviewing it she found something strange
when she looked in it right on with the
winds coming perpendicular to the tower
she was able to get the numbers to stack
up however when she twisted that
building
45 degrees and had these quartering
rings she was unable to get the design
to stack up
under the numbers that she was putting
together having concerns about this and
obviously thinking that she had made a
mistake she contacted her lecturer
and he advised her to contact the actual
engineering firm is he how they solved
this problem
see diane took the phone and called
william lemaitre and discussed with him
her findings and he was quite fascinated
see this is potentially where
expertise will let you down you see
these quartering runs when you twist the
normal building
it's increasing your lever arm so the
building is actually stronger under
these type of actions however
due to the unique feature of having
these columns central this lever arm is
much less so true by this
the measure hook action and actually
started to do the numbers
you see as diane didn't have those
preconceptions from designing many
buildings
she looked at the building at the hole
and checked every direction
to make sure it was designed in the
right aspect she was able to find the
fatal design flaw
that the world-renowned engineer
overlooked and this is where he started
to have a chilling thought
when he did the numbers he realized
these type of courting rings
actually increased the stresses in the
building in excess of a hundred and
forty percent
so la measure at this time realizing
these increased forces
did everything he could to try and
reduce the loads and justify the
structure
so what he was looking at is essentially
there's a tuned mass stamina
inside the building what this does
counter balances the building under the
actions of wind loads
and helps reduce the sway of the
building thus reducing the loads
however this is still not enough so then
he took
to additional wind tunnel testing in the
university of ontario
and when they did the boundary layer
testing they found that the tower
was actually highly susceptible to these
type of actions
due to the dynamic properties of the
building and actually
increased the wind loads and when he was
looking back through his documents he
also realized there was another design
change
that made this area even more critical
you see these whole welded frames at the
time the design in the building
were called up to be welded full
strength welded connection
however during erection the steel
fabricator was finding it hard to put
the structure together as it was
documented
so they actually requested a design
change to allow them to have bolted
splice connections
which were approved so when he added up
both these quartering rings
and these bolters plus connections he
found they're undesigned
and they're overstressed by 160 this was
extremely worrying
as this made it highly susceptible to
any wind loans it can actually fail as
low as a 70
mile per hour wind now for new york that
is a really low wind
and it's quite a common occurrence so
this discover filler measure was both
surprising
and chilling and facing potential
bankruptcy
litigation and professional disgrace and
the potential catastrophic collapse of
this building there was only one path
and this was for him to take action
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let's keep going the measure then came
with a plan
and set up a series of meetings with
both the architect
his insurance company the board that
owned the citicorp centre and the board
of engineers
for new york and they had confidential
meetings about the problem and he
explained to them
what the issue was and the fact that
need to be addressed
he also came there with a solution now
that solution was to weld these bolted
connections together
now this is where they hit a potential
crossroads
as should they notify the public or not
and at the time
it was decided to not notify the public
and has made
unduly distress and panicked the
residents in the local area
and they only released a vague press
release that the building was going to
get maintenance
and repair works over a series of months
as the work was starting to come in this
story nearly leaked to the public
so an architect actually contacted the
measure's office
realizing something was up with the city
thought center and when le measure went
back to contact that
same journalist he was not there you see
they all went on strike for better
paying conditions at all the news
agencies
where they sort of got some of their
luck as the story essentially evaporated
and it was never followed on beyond this
point and now this is where the planning
phases
was beginning as well the team had an
understanding
how susceptible this tower was to wind
loads
they set up an evacuation plan and wind
and door monitoring processes and what
would trigger a potential evacuation an
area that was required to evacuate
around the building required the
evacuation over 200
000 people this would need quite
extensive planning
for additional shelter food and
relocation
over a period of time that the store may
hit this was put together with the mayor
and the red cross a potential action
plan that may need to be activated
in the event of a certain storm heading
towards new york
and we also bring up that tune mass
dampener that we bought at the start of
the building it was actually one of the
first tuned mass standards to be
installed on
any tower in the world and you see
there's actually two types of tree mass
standards you either have an
active tune stamina that requires
electricity through activation and
pulleys
better tune the wind loads out it gives
you a lot broader range that the tuned
mass standard can be activated in so
essentially making it more effective at
tuning out a wider range however it does
require a constant electricity grid
whereas you have another one which is a
passive tree mass damper which is
essentially like a giant pendulum
or water there's different types of
these that can do this type of work
however
they are more limited as they
essentially be constructed for a certain
wind or vibration range however they do
not require the electricity
fortunately fuller measure was also a
curse as well the one at the city called
tower was an active one so it required
that full time constant electricity to
ensure that this tune mass dampener
would always have electricity
whenever it needed it they set up a
series of backup generators to ensure
there was a power
during an event which would potentially
knock out the electricity grid this
ensured them that they'd have constant
electricity over a
period of time and make sure that tree
mass dampner was in his active state
whenever it was needed they also
contacted the manufacturer of the tune
mass damper to ensure that it was in
peak octal from addition
at any time that needed to be activated
so this is where the repair work started
under the command of the measure
although measure was constantly doing
numbers
graphs and figures of all the
consequences that could potentially
happen
and directing which connection to
strengthen next
so the building progressively got
stronger over time and required
bigger win that would activate that
evacuation process
the work was so extensive for them to
complete it in a reasonable time
that to hire pretty much every welder
within a hundred mile radius of new york
and they even sped up the certification
process through the new york board for
construction
where they got more people certified in
a quicker time to ensure the workforce
was extensive enough
to allow for the quick rectification of
this structure
and under the command of the measure it
was almost to military precision as they
wanted to keep it somewhat quiet the
only time was able to be done was the
secret to sea of night however it did
continue on
seven days a week see the carpenters
would start work at five pm where they
would come in
after the office workers had left where
they would expose the critical joints
the measure had noted
and set up protective screens and then
at 8pm the welding would start
and this is where the strengthening
worked and the towers began and this
would
continue on until 4am at which point
they would stop and a series of
labourers would come in
and clean up the area so when the office
workers started back in the morning
they were none wiser to the extent of
work that were being done a couple of
weeks in
just starting the repair work a
hurricane formed off the coast of new
york
it was actually tracking to actually
strike new york and this is where
everyone started sweating blood as low
measure recalls
as they started to fear that they'd need
to activate that evacuation plan and
preliminary plans were actually set into
motion however just before they needed
to activate it dorm veered off
and went back out to sea so they never
had to initiate the evacuation plans
after another months of work on the
tower the building was fully
strengthened
and a minor litigation therefore ensued
the measure came to the city group and
offered them full extent of his
insurance which was two million dollars
as rumor has it this didn't even cover
the full extent of the repair works that
needed to be undertaken and the public
didn't actually become aware of this
fatal flaw until
20 years after his actual event the
measure was both praised and criticized
for his actions
as he didn't take the due diligence that
he needed to do to ensure that all the
critical win cases were checked
especially on a state-of-the-art
building that required a unique design
solution
overlooking the potential obvious
solution that was found by this graduate
engineer he was also not aware of the
design changes that happened during
construction and a potential impact it
had on its design as well
and also being such a state of that
building as well it was just reliant on
the code which potentially didn't
cover all the aspects that he needed to
on such a unique build
his public statements both got
criticized heavily as well
as he essentially kept the public
undercover they didn't actually know the
true extent of the damage that it
could occur to the building it couldn't
assess for themselves whether they
wanted
to be in the area or not and also by
keeping it from the
engineering fraternity it potentially
allowed for future buildings to miss
this obvious mistake
being a world-renowned engineer this was
something that his team
should have been able to pick up and if
they missed it it's likely that other
engineers would as well
so by not letting other people know much
sooner it potentially could have led
to other buildings having this fatal
design floor as well but the measure
should also be praised for his act you
see
he took action when he found the problem
instead of just closing his eyes he
notified the people
with no regard to what that meant for
himself and when an undergraduate
engineer
came to him with a problem that she
thought was wrong with the tower he
listened to diane
took her concern seriously and realized
that he had made a fatal mistake
see in the end i feel this is really a
tale of
engineering ethics in its finest yes he
did make some mistakes and no one is
perfect and we should
really never shoot the messenger the
fact that he actually took action and
fixed it
should be praised what do you think do
you think the measure's action should
have been any different
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and i hope to see you next week bye