Chapter 20 Why the WTC Collapsed

Question 1

what type of collapse was the WTC?

Answer 1

pancake

Question 2

How was the construction of the WTC towers different from other high-rise buildings built before it?

Answer 2

Twin towers used radically different design. It had exterior load bearing walls (tubular in design), and floors free of any interior columns except at the core area. 21, 10ft apart

Question 3

What is the most notable change in modern high-rise construction in this country

Answer 3

the trend to use more steel and shaped lightweight steel into tubes curves and angles to increase its load bearing capacity

Question 4

unprotected steel works, sags, beings, and collapses when heated to the normal higher temperature of about

Answer 4

1100-1200 (WTC chapter) p273

1000-1100 (the rest of the book) p143-145

Question 5

what is the best fire resistant building in America, they limit and confined fires best and suffer fewer collapse

Answer 5

reinforced concrete structure, examples are pre-World War II buildings such as the Empire State building

Question 6

was a ratio of concrete to steel in the Empire State building

Answer 6

60:40, WTC 40:60

Question 7

what has led to the reduction of the safety factor

Answer 7

computer aided design, computers allow engineers to reduce the mass of the structure with more accuracy, the structure is built exactly to the specifications of the code… no extra safety factor

Question 8

was the progression of the removal of concrete from high-rise construction

Answer 8

1. concrete was eliminated from the stone exterior wall, replaced with glass curtain wall
2. concrete floors were reduced to 2-3 inches of concrete poured on corrugated steel sheets
3. masonry enclosure for stairs and elevators, replaced by several layers of sheet rock
4. masonry smoke proof tower was eliminated
5. the solids to being was replaced by the steel truss
6. concrete brick encasement of steel columns and girders replaced by lightweight fire retardant spray on foam

Question 9

how do performance code differ from specification code

Answer 9

specification code states specific type of material used to protect the structural steel and enclose fire stairways and elevator shafts… while performance code to state the hour of fire resistance required

Question 10

the problems with spray on foam protection

Answer 10

1. failure to prepare the steel for spray on coding adhesion
2. uneven application of the spray on retardant
3. variation of spray on material during manufacture makes it ineffective
4. lack of thoroughness in covering steel during application
5. failure to replace spray a material dislodged by other trades people
6. HVAC can blow off fire retardant

Question 11

what are the 15 requirements that Dunn thinks should be required of all high-rise buildings

Answer 11

1. evacuation drills, to know emergency evacuation time
2. exit and stairway width, should have sufficient capacity to allow evacuation within time limit of the floors fire resistance rating
3. steel columns, girders, and floor beams should be encased in concrete
4. limit use of lightweight bar joist floor truss
5. use smoke proof stairways
6. stair and elevator shaft to be enclosed in concrete
7. phase 3 elevator, for access to upper floors
8. better insulation of electrical wiring in elevators
9. limit the ducts of HVAC, to only service 1-2 floors
10. prohibit tube frame, structural framework as used WTC
11. greater thickness of concrete floors
12. zero tolerance for non-sprinkler high-rise buildings
13. antenna installed in high-rise, enhance FFer com
14. federal/ port authority buildings voluntarily comply with fire code
15. pre-fire plan for our high-rise

Question 12

what is the goal of fire resistive construction?

Answer 12

any fire to be confined to one floor, by an explosion or collapse that would destroy part of the compartmentalization…. this is clearly not the case therefore the term fire resistive construction is meaningless

Question 13

why does “passive fire resistive” no longer exists

Answer 13

the HVAC system, ducts, shafts, poke throughs penetrate fire resistive floors walls and ceilings.. HVAC being the biggest problem

Question 14

what is the problem with standard of fire resistance rating

Answer 14

their century-old and based on small samples exposed to fires… before plastics

Question 15

what is the weak link in the construction of fire resistive high-rise buildings

Answer 15

floors, floor supports must be tested in large-scale fires simulating complete burnout of the floor

Question 16

what was one of the give aways to the construction and industry from the 1968 New York City building fire codes

Answer 16

permission to have one single water riser supply both the sprinklers in the standpipe system

Question 17

what should the standard beef for fire department radio communications in a high-rise building

Answer 17

radio transmissions travel from the lobby command post to the roof and from the lobby command post to the lowest grade.

Question 18

While remote exits important and what is the current definition of remote in building construction

Answer 18

remote exits are important so if one should be damaged there is another on another section of the floor…. the distance defined as remote today is 15 feet

Question 19

was a phase 3 elevator

Answer 19

phase 3 elevators one that is enclosed and protected from smoke fire and host range and sprinkler water so that it can safely be used by firefighters or occupants during a fire

Question 20

and eight year study of 179 major high-rise fires in New York City found that elevators failed …

Answer 20

elevators fail due to fire, heat, water 1/3 of the fires

Question 21

while our firefighter radios used by the firefighters a national disgrace

Answer 21

1. they do not work in high-rise buildings, tunnels, subways
2. no interconnectivity with the police and ems
3. interference from commercial radio signals
4. single channel for dispatch and Fireground messages
5. wildfire shelters block radio signals
6. interference from broadcasts cable company antennas

Question 22

are the short-term and long-term recommendations by McKinsey for communications in a high-rise

Answer 22

short-term solution, portable booster

long-term solution, permanent booster infrastructure- installed in high-rise

Question 23

was is a major obstacle impeding effective firefighter radio transmission

Answer 23

the absence of a standard for fire department transmission radios

Question 24

high-rise buildings are small cities and should have a person dedicated to the fire safety of the building… this person would assist personnel upon arrival and is trained and certified in building fire safety fire prevention and fire evacuation of occupants….

Answer 24

fire safety director

Question 25

what is the main problem with coordinated incident management system CIMS

Answer 25

CIMS has police in command of fires, emergency medical incidents, hazardous material incidents, building collapses, search and rescue, and mass casualty when terrorism suspected. police will have command of these incidents that they do not train for, do not do every day, and to which they are not committed