Question

can someone please answer these questions based on the CitiCorp NY Skyscraper

Q1: What were some of the tradeoffs in the construction of the Citiccorp Center?

Q2: What do you think of the risk management strategy that was employed?

Q3: Should builders have to tell the engineers every change they are making in their plans?

Q4: What do you think about the fact that the emergency repairs were kept secret?

Q5: How can a builder know which changes are important and need to be told to others and which don't matter?

Q6: What is the responsibility of building inspectors, councils etc to ensure that codes of practice followed?

Answer 1

CITI CORP CENTER

SOLUTION 1

Major Tradeoffs

These tradeoffs were donw to overcome certain problems faced in the building as given below

PROBLEM 1-Quarter winds are more stronger than simple wind direction, for this he made all the possible calculations and decided to provide welded connections with columns of v shaped and height of about 8 storeys

PROBLEM 2-They prepared to employ bolted connections in the building , which was much more dangerous, and LeMessuriercame to know this just about a few days prior to this work

PROBLEM 3-This was the problem of advantageous thing, 370t concrete mass damper which was employed over the building may not work when high speed wind is blowing due to power failure , so proper power is needed to keep it working for when it is required

trade off donw to overcome these issues were :-

• Providing steel plate welds above bolted connections
• Columns at the center rather than at corners
• Providing extra power supply source in order to maintain mass damper working in case of heavy wind and power failure

1. COLUMNS AT CENTER RATHER THAN AT CORNERS

To save the space and corners ,they employed columns at center of the building rather than placing it to all corners which is as suggested in codes of new york city standards

this was the major drawback and trade off of the structure ,designed and engineered by  LeMessurier

He designed this kind of thing to overcome various expenditure and problems , which can be felt with columns at corners ,

He considered quarterly wind or better to say wind blowing at an angle of 45 to the building, or cross winds , so in order to resist this kind of problem he employed columns at the center of each side ,

but problems occurred , as given above

• PROVIDING STEEL PLATES AND WELDING THEM ABOVE BOLTED CONNECTIONS

To overcome problem 2 LeMessurier employed plates over the bolted connections and weld them in order to increase its strength , so that it could face higher order wind forces ,

in doing so cost has increased a lot as this was a mistake ,but this step increased its strength from wind of intensity 1 in 16 years to 1 in 700 years ,as it was majorly focused to fight the wind loads

welding of the bolts were not possible from inside the building , so steel plates are provided on top of the bolts and welding it properly , and covering them after that , that is cladding

so it has achieved dual strength one of bolted connnections and supported by welding , and due to steel plates , welding area has also increased providing higher stability to the building

• PROVIDING POWER SUPPLY DURING POWER FAILURE TO THE MASS DAMPER DURING HEAVY WINDS

  This was done to overcome problem 3 and to provide extra safety when required against sway and damping vibrations to the building

As due to high wind ,major problem is of power cut , because of this our mass damper couldn't work at all so it doesn't fulfill its purpose ,

To make it work continually extra power source have been provided , it increased the cost but has caused safety as well