Ch. 20 Why the WTC collapsed

Question 1

The WTC was built using exterior hollow tubes as load bearing walls, carrying the building’s vertical load. The thickness near the top was how thick?

Answer 1

Only a 1/4 inch thick

Question 2

WTC

The only interior columns were located in what area of the bldg.?

Answer 2

The only interior columns were located in the CORE AREA. Floor sections consisted of 60 ft. steel bar trusses from core to outer wall.

Question 3

WTC

How many inches of concrete floors was poured on fluted metal decks that were supported by bar joists?

Answer 3

3 inches of concrete

Question 4

WTC

Steel framing is economical while concrete is costly. The best fire resistive bldg. is what type of structure?

Answer 4

A concrete structure. These structures limit/confine fire the best & have less collapses. (reinforced concrete structures)

Question 5

WTC
Application of sprayed on fire retardant material (SFRM) over primer painted steel reduces its effectiveness by how much?

Answer 5

1/3-1/2

Question 6

WTC
What are the 3 necessary criteria for SFRM to be effective?
ACT

Answer 6

Adhesion- so it’s not blown off due to air movement and vibrations
Consistency
Thickness

Question 7

WTC
What type of collapse is a danger in buildings that have the following construction?
-Large open floor area that has no supporting columns or girders reinforcing the long span floor beams.
-Lightweight high-rise bldg.’s with steel trusses used over large open floor areas, eliminating steel columns and girders, in order to create more rentable space.
-Have the weight of masonry removed so a framework of lightweight steel girders and columns can be used.

Answer 7

A PROGRESSIVE Collapse