CHAPTER 7

Question 0

What are examples of Cold Drawn Steel that fails around 800 degrees

Answer 0

Steel tendons used for tensioned concrete and for excavation tie backs and elevator cables

Question 1

Characteristics of steel according to Brannigan

Answer 1

Substantial elongation takes place in steel at ordinary fire temperatures (1000 Degrees)
If steel cannot elongate because of restraint, it will buckle or overturn
When heated to higher temperatures (above 1300 degrees) which are common at major fires, the yield point of steel is drastically reduced. At this temperature steel may fail
While structural steel fails around 1300 degrees, cold drawn steel will fail at about 800 degrees.

Question 2

At excavation sites, if ground exist, cold drawn steel is placed into holes driven into the ground, tensioned, and used as tiebacks. If these tiebacks are exposed to fire, and the tensioned portion of the cables reaches 800 Farenheight, it may fail. Therefore tiebacks exposed to fire

Answer 2

Should be cooled continuously from a safe distance

Question 3

Characteristics of steel

Answer 3

• If steel cannot elongate because of restraint, it will buckle or overturn
• Steel is a good thermal conductor, so it transmits heat readily
• If water is placed on hot steel that is elongating the cooling effect of the water will draw it back to its original dimensions
• If a steel beam that has passed its point of strain is cooled, it will keep its deformed shape

Question 4

As steel is heated at a fire, it will elongate expanding 6-7% for each 100 degree in rise in temperature, regarding the expansion

Answer 4

• The expansion rate increases as the temperature rises
• Heated to 1000 degrees, a steel beam will expand 9 1/2 inches over 100 feet in length
• In hot fast fires, failure temperatures are reached rapidly and the lateral thrust against a wall will be minimized
• If steel is raised above 1000 degrees it starts to lose strength rapidly