The Hollow Tube Idea: teacher key

How Buildings Stand Up, grade 11 edition, written for 11th grade. To go higher than steel frames allowed, engineers turned towers into hollow tubes, added giant dampers and sank piles deep into the ground. A New York tower shows what happens when a hidden flaw is found.

Read the book. Print this page for the key.

Questions and answers

1. Above about how many stories does a plain steel frame become uneconomic?
   • 10
   • 40 (answer)
   • 100
2. What is a bundled tube?
   • One thick tube
   • A tube made only of glass
   • Several tubes tied together (answer)
3. What does a pile cap do?
   • Spreads the load among a group of piles (answer)
   • Covers the top floor
   • Holds the elevator
4. Why does a damper's tuning need care?
   • Its weight never changes
   • The building's resonant frequency can drift with wind, temperature and humidity (answer)
   • It only works in summer
5. What did the Citicorp story become a staple of?
   • Engineering ethics teaching (answer)
   • Wind tunnel design
   • Elevator safety rules

Words

• cantilever: fixed-end beam
• lateral: sideways
• pile: long deep column
• ethics: right conduct