[BC] Strong buildings vs open space

[Mike McCarthy]

Wow Robert...we agree on something.... I didn't think it possible 
today...;-)  I appreciate the compliment of Chicago's building engineering.

Seriously, the design engineers for Hancock and Sears did a very quick 
analysis of a similar incident involving each after 9/11.  They concluded 
the X brace design for Hancock would easily survive even a corner hit at a 
X joint because the large cinder block and poured concrete core is designed 
to support the building's weight.  Conversely, if the core and part of a 
face was taken out, the outer shell would still hold because the x-bracing 
on three sides and interior columns would absorb the weight. In some ways, 
the building was over designed in 1965.  It's a very rigid building...and 
one which I think might survive a tornado.

Sears is a very different design where each of the nine 75 ft. square 
sections are designed to stand on their own and flex. Even at the 
penthouse, the vertical columns spaced at 25 ft. are 24" I' beams which are 
1" thick and spreaders some 10" on either end. There are center columns 
spaced at 25 ft. through all the building as well.  So think of it really 
as a 225 ft. square building with columns every 25 ft. no matter which way 
you look.

If a large plane hit the building, the plane would be sheered apart by the 
exterior bearing columns as the building flexed lessening the damage to the 
interior of the building.  Which is unlike the WTC buildings where the 
planes plowed right through the exterior "skin" nearly intact all the way 
to the buildings' cores.

For buildings completed in 1969 and 1982 respective and the designs done by 
hand, they're both an amazing feat. Sears still moves around in wind 
though.  In fact, when I was there during a 60 MPH wind event on the 
ground, I saw water sloshing around in the toilet on 102.  And when you get 
to the ground, you have rubber legs for the first 100 steps or so...

So what does this have to do with radio?  Simple...the sites are well built 
to survive the nasty midwest winters and spring storms...and keep on going.

MM



At 06:38 PM 3/5/2007 -0500, Robert Meuser wrote
>Mike McCarthy wrote:
>
>>
>>Sears Tower and John Hancock, as well as most other tall buildings here 
>>in Chicago do not follow that design philosophy.  Only the AON building 
>>here has open floors.  But the building is also a much smaller building 
>>and made totally of steel reinenforced concrete. Not open face 
>>steel.  All the major buildings here have multiple columns in the 
>>buildings inside the outer perimeter.  In fact, Sears is made of 9 very 
>>independent columns mated together for rigidity.
>
>I was looking at the Sears tower when I was in Chicago last year. No way 
>would that have come down like the WTC.  There is a reason Chicago is the 
>home of American architecture.
>
>R