1. Fire-Resistive Construction
Chapter 11
Fire-Resistive Construction

2. Objectives
Recall the difference between noncombustible and fire-resistive construction.
Describe different types of concrete structural systems.
Describe the two types of prestressing.

3. Objectives Describe the hazards of formwork.
Describe the methods of fireproofing steel and of ensuring a level fire resistance in concrete.
Describe how concrete and concrete structural elements react to fire.

4. Introduction Fire-resistive construction Considered to be the best
Most resistant to collapse and does not contribute fuel to a fire
Is given the largest permissible area and heights

5. Concrete Cementatious material produced by a chemical reaction
Cures indefinitely
Low temperatures retard the curing of concrete.
© Christina Richards/ShutterStock, Inc.

6. Concrete Weak in tensile strength and has poor shear resistance
Good compressive strength

7. Concrete Structures Pre-World War II
Suitable only for structures in which aesthetics played little part
Built of steel frames and fireproofed with concrete
Cinder blocks use cinders as the aggregate.
Concrete blocks use other materials for aggregate.

8. Underwriters Blocks
Concrete blocks produced under Underwriters Laboratories’ classification
Manufacturer’s certificate gives the type and number of units delivered to a specific job.
Blocks must meet fire resistance standards.

9. Today’s Variety of Concrete Structures
Use variety of building construction elements
Steel-framed buildings now often have cast-in-place concrete floors.

10. Today’s Variety of Concrete Structures
Architects may emphasize concrete construction.
Decorative brick veneer is used to conceal the concrete construction.
© Adriano Castelli/ShutterStock, Inc.

11. Steel vs. Concrete Framing
Designer preferences
Some design in steel.
Others prefer concrete.
Some buildings are concrete-framed and steel-framed mixed together.

12. Fire Department Problems
Problems with concrete construction
Collapse during construction with no fire
Fire during construction
Fire in completed, occupied buildings

13. Types of Concrete Construction
Cast-in-place
Plain, reinforced, and post-tensioned concrete
Precast
Plain, reinforced, and pretension concrete

14. Concrete Definitions Aggregate Cast-in-place concrete Casting Chairs
Composite and combination columns
© Dick Stada/ShutterStock, Inc.

15. Concrete Definitions Composite construction Continuous casting
Continuous slipforming
Drop panels
Courtesy of Glenn Corbett.

16. Concrete Definitions Flat plate structural system (or continuous beam)
Footings
Lally columns
Lift slab
Courtesy National Institute of Standards and Technology

17. Concrete Definitions Monolithic construction Mushroom caps
One-way structural system
Plain concrete
© Brad Wynnyk/Alamy Images

18. Concrete Definitions Pretensioning and post-tensioning
Precast concrete
Reinforced concrete
Reinforcing bars or rods

19. Concrete Definitions Slipforming Spalling Temperature rods
Two-way structural system
© Marek Pawluczuk/ShutterStock, Inc.

20. Virtue of Columns High compressive strength and low cost
Columns are of reinforced concrete.
Steel reinforcing rods carry some of the compressive load.

21. Virtue of Columns
The compressive strength of steel is many times that of concrete.
Ridges added for bonding strength
© hxdbzxy/ShutterStock, Inc.

22. Virtue of Columns
Epoxy and stainless steel coatings minimize corrosion.
Glass fiber polymer reinforcing rods have twice the strength of steel.

23. Increasing Column Sizes
Unsatisfactory in modern construction
The useable area would vary from floor to floor.
Overcome by increasing the size of the reinforcing steel as the loads increase

24. Reinforcing Rods Long with a relatively thin diameter
Ends of rods are connected.
Ties or hoops join the rods in a column.
Ties cut the long slender column into a number of relatively short columns.

25. Beams and Girding Plain concrete beam
Strong in compression, weak in shear
No tensile strength
When a beam is loaded, it deflects.
Deflection brings compression in the top of the beam and tension in the bottom of the beam.

26. Beams and Girding Cantilever beam Tension is in the top of the beam.
Reinforcing rods are in the top of the beam.

27. Beams and Girding Continuous beam supported at more than two points
Tension in the top of the beam in the area over the tops of the columns
Tension in the bottom of the beams between columns
Vertical reinforcing bars in concrete beams are called stirrups.

28. T-Beams There is neither tension nor compression in the beam.
Has the neutral plane coincide with the bottom of the wide, thin floor slab
Courtesy of the estate of Francis L. Brannigan.

29. T-Beams
Double T’s are floor slab and beam combinations with two beams.
Floor beam combinations with four beams are also manufactured.

30. Autoclaved Aerated Concrete Units
All components of concrete plus aluminum powder
Lighter than traditional concrete
Easily cut
Four-hour ASTM rating
© pryzmat/ShutterStock, Inc.

31. Concrete Floors First used for leveling brick and tile arch floors
Early floors were built of individual beams supporting a floor slab.
Hollow tiles lightened concrete floors.

32. Waffle Concrete
Closely spaced beams are set at right angles to one another.
Unnecessary concrete is formed out.
Courtesy of Glenn Corbett.

33. Lighter Construction Floor may be just a flat plate.
This gives a smooth surface.
Easily finished

34. Left-in-Place Form
Occurs when concrete floors are cast onto corrugated steel
The steel provides necessary tensile strength.
If the bond fails, the floor section may fail.

35. Precast T-Beam Units
Additional concrete is often cast-in-place on top of the units.
Entire unit becomes an integral beam-and-floor element.

36. Precast T-Beam Units
Cylindrical openings can be cast lengthwise through the units to remove unnecessary weight.
Concrete floors may be simply load-bearing.
Courtesy of the estate of Francis L. Brannigan.

37. Older Building Codes Concrete floor can be in ordinary construction.
Case example:
Concrete topping over wood beams concealed the destruction of the beams by fire.
Four fire fighters died.

38. One-Hour-Rated Designs of Wood Floors
Lightweight concrete topping as much as 1 to 1½ inches thick
Thickness retards the passage of heat through the floor.
NFPA 251 (ASTM E-119) fire resistance standard

39. Cast-in-Place Concrete Floor
Can be a hazard during construction
A slot is left in the wall at the point where the floor is to be cast.
If a windstorm occurs during the time that the slot is open, a collapse may result.

40. Concrete Floors in Steel Buildings
May be precast or cast-in-place
May be only load-bearing or provide structural stability

41. Concrete Floors in Cast-In-Place, Concrete-Framed Buildings
Cast integrally with columns
Provide a monolithic rigid-framed building
May be pinned
May be connected as a monolithic unit

42. When Slabs Are Laid Down
A space is left between them.
Protruding bars of one slab extend past the ends of the protruding bars of the other slab.
The sections are joined by a wet joint.

43. Concrete Floors in Precast, Pinned Concrete Buildings
May not contribute to the building’s structural stability
Precast columns are often built with haunches or shelves.
Steel plates imbedded in the concrete may be welded together.

44. Prestressed Concrete Recently developed
Engineered stresses placed in architectural and structural concrete
Analogy: A row of books side by side, before and after being threaded together with wire

45. Special High-Strength, Cold-Drawn Steel Cables
Similar to those used for suspension bridges
These or alloy steel bars are commonly used in prestressed concrete.
Known as tendons, but also called strands or cables

46. High-Tensile-Strength Wire
Ordinarily used for prestressing
More sensitive to high temperatures than structural steel
Complete loss of prestress at 800˚F

47. Two Methods of Prestressing
Pretensioning
Done in a plant
High-tensile-strength steel strands are stretched between the ends of a form.
After processing, stretched strands draw back, thus compressing the concrete.

48. Two Methods of Prestressing
Post-tensioning
Done on the job site
High-tensile-steel strand wires are positioned in the forms.

49. Two Methods of Prestressing
Post-tensioning (cont’d)
After processing, steel tendons are stretched and anchored at the ends of the unit.
Stressing the tendons or “jacking the cables”
Courtesy of the estate of Francis L. Brannigan.

50. Bridge Girders
Some are tensioned enough to make shipment possible, then post-tensioned after being placed.
Cement paste might be forced into the space between the tendon and the concrete to provide a bond.

51. Ordinary Brick Bearing Wall Buildings
Walls must increase in thickness as the building’s height increases.
Limit is generally about 6 stories.
Recent years, can build to 20 or more stories

52. Ordinary Brick Bearing Wall Buildings
Construction methods allow higher buildings.
Two wythes of brick are built.
The width of one brick is left between them.
Reinforcing rods are placed vertically.
Concrete is poured into the void.

53. Reinforced Masonry Widely used to resist earthquakes
Unsuitable for multistory buildings in which large clear spans are required
Apartment houses and motels are well adapted to this method.

54. Special Cases Low-rise buildings
Recent designs have eliminated reinforced concrete in the wall.
High compressive-strength bricks and special mortar are used instead.
Masonry wall-bearing building can be several stories high.

55. Special Cases Concrete block Has become popular for some resorts
With outside open-air stairways and balconies, life safety is achieved.

56. Collapse Under Construction
Concrete structures under construction sometimes collapse.
Fire department rescues construction workers.
Fire officers should be well informed on the legal position of the fire department.

57. Ordering the Removal of a Dangerous Structure
Power given to the building commissioner
Fire department has no right to demolish such a structure.

58. Lawsuits
Common today
Owner, architect, general contractor, subcontractors, and victims attempt to determine financial responsibility.
After collapses, some of those involved may try to cover up their actions.

59. An Industry Warning
Experts have warned of the collapse hazard of concrete structures.
Design engineers should use construction loads as governing loads in structures.

60. Problems of Falsework Falsework
Temporary structure to support concrete work in the course of construction
Can represent 60% of the cost of a concrete structure
© photoslb/ShutterStock, Inc.

61. Concrete Formwork
Designed without the extra strength calculated into a building to compensate for deterioration
Built at the lowest possible cost
Formwork failures can occur but are surprisingly rare.

62. Falsework for Walls or Columns
Must have adequate strength to resist the pressure of heavy fluid concrete
As concrete sets, pressure is reduced due to internal friction.
Setting of concrete is temperature dependent.

63. Reshoring Concrete Concrete requires time to cure.
Formwork is then removed.
Reshoring is putting shores back in place to help carry the load.
Reshoring means concrete is not yet set.

64. Collapses of Floors
Many involve formwork supporting newly cast or high bay floors.
Proper cross-bracing can help prevent this.

65. Collapses of Floors Formwork can also be a problem.
Often rests on the ground
Mudsills are the planks on which the shores rest.
If mud is involved, bearing may be inadequate.

66. A Widely Believed Fallacy
“Reinforced concrete which has set hard to the touch usually has developed enough strength to be self-supporting, though it may not be capable of handling superimposed loads.”

67. Skyline Towers Collapse
Skyline Towers collapse in Arlington, Virginia, 1973
Collapse proved the fallacy.
Courtesy of the Fairfax County Fire and Rescue Department.

68. Skyline Towers Collapse
Shoring had been removed from the topmost floor.
The floor collapsed, and the collapse was progressive.

69. Lessons from Skyline Towers
Removal of shoring by laborers is no different than removal by fire.
Any concrete formwork failure presents the likelihood for catastrophic collapse.
Few concrete buildings can withstand the collapse of one floor onto another.

70. Hazards of Post-Tensioning
Hydraulic jacks are used to tension the tendons or jack the cables.
No bond exists between the tendons and the concrete.

71. Hazards of Post-Tensioning
Weight of concrete transfers to columns only when tensioning is complete.
Case example:
The Skyline Towers garage was made of post-tensioned concrete.
Poor sheer resistance led to collapse.

72. Collapse of Reinforced Masonry
Used widely in construction
Workers might overload a floor portion.
Case example:
In Pittsburgh, PA, an excess load caused the partial collapse of several stories of precast floors.

73. Collapse of Precast Concrete
Precast concrete buildings under construction are unstable.
Temporary bracing holds units in place.
Wooden temporary shoring might also be used.
Case example:
In Montgomery County, MD, three-story garage collapsed due to oversized washer.

74. Lift-Slab Collapses Lift-slab construction
Ground floor slab is cast first.
Bond breakers are used between the slabs.
Slabs are raised to the columns.
Each floor is temporarily connected to the columns.

75. Lift-Slab Collapses Case example:
L’Ambience Plaza concrete building collapse in Connecticut was due to the failure of a single connection.

76. Lift-Slab Collapses When do the accidents occur? Case example:
While the slabs are being lifted or while no lifting is being done
Case example:
In California, a roof slab was lifted to columns 3 inches out of plumb.
As an attempt was made to pull the slab back into place, it collapsed.

77. Fire Problems of Type I Buildings Under Construction
Concrete buildings under construction can present serious fire problems.
Fire in formwork can easily result in major collapse.
Little understanding of potential catastophe

78. Potential Fires at a Construction Site
Causes include welding, cutting, and plumbers’ torches; temporary electrical lines; and arson.
Fuels are readily available.
Glass-fiber formwork is also combustible.

79. Hazard of Heating
Burning of scrap wood in steel barrels and the use kerosene heaters are hazards.
Liquefied petroleum gas (LPG) is also dangerous.

80. Codes for LPG Store gas away from any open flames. Case example:
1963, LPG explosion at the Indianapolis Coliseum
Caused when a leaking gas-fired cooker cylinder exploded and gas reached heater flame

81. Codes for LPG Install excess flow valves. Case example:
In one city, gas is stored and piped with plastic tubes at ground level
Hazard exists, should line break

82. Hazards of Post-Tensioned Concrete
Catastrophic fire collapse potential
Include bridges and parking garages
Falsework fire could cause the sudden collapse of an entire concrete floor slab.
After tensioning, the ends of tendons are left exposed.

83. Hazards of Post-Tensioned Concrete
Hanging tendons can fail at about 800˚F.
Excess tendons are rolled up and attached to a wooden rack.
Rolled-up tendons are heat collectors.
Failure of tendons will cause the collapse of that part of the structure.

84. Protection of Tendons
Insist on protecting tendon anchors immediately after tensioning is completed.
Insist on temporary protection for incrementally tensioned tendons.

85. A Total Collapse: Case Example
A post-tensioned building under construction in Cleveland, Ohio, suffered a falsework fire.
After a second fire, the entire 18-story building collapsed.

86. Precast Buildings Pose unique hazards while being constructed
Construction involves erection of precast concrete units.

87. Precast Buildings
Columns can be braced with wood rather than by telescoping tubular steel braces; wood is flammable.
Loss of temporary support may cause a collapse.
Cold-drawn steel cables often provide diagonal bracing in precast buildings; these fail at 800˚F.

88. Cantilevered Platforms
Used by cranes delivering materials to buildings under construction
Are braced by wooden shores that would fail in a fire

89. Tower Cranes Supported on the building’s structural frame
Weight of the crane may be distributed over several floors by falsework.
A fire involving this falsework can bring down the crane.

90. Falsework on a Completed Floor
Should be investigated
May be supporting a patch over a hole
May be supporting a heavy load such as the crane

91. Falsework: Case Example
Formwork for concrete placement burned on the 23rd to 25th floors of a high-rise.
Operator was trapped in his cab.
He was protected with a heavy-caliber stream from a nearby roof until rescued.

92. Fire Problems in Finished Buildings
Concrete construction
Thought to be truly fireproof
Later, it was learned that concrete, like any other noncombustible material, can be destroyed by fire.

93. Characteristics of Concrete
Inherently noncombustible
Some people confuse noncombustibility with fire resistance.
Neither is synonymous with fire safety.

94. Safety of Concrete Construction: Case Example
Reinforced concrete Joelma building in Sao Paulo, Brazil, burned in 1974.
Resulted in 179 deaths but minor damage to structure

95. Fireproofing (Insulating) Steel
Has a fire resistance rating if the protection system previously passed a standard fire test
No such thing as a truly fireproof building
Fireproofed steel is protected steel.

96. Types of Fireproofing
Individual fireproofing provides protection for each piece of steel.
Methods include encasement and spraying.
Membrane fireproofing does not protect individual members.

97. Types of Fireproofing One method uses a rated floor–ceiling assembly.
Underwriters Laboratories can test a roof and ceiling assembly.
NFPA 251 (ASTM E-119) standard fire test

98. Hazards of Floor–Ceiling Assemblies
Can present a serious menace to the safety of fire fighters
Assemblies need to be assembled exactly as performed in the laboratory.

99. Ceiling System
At the mercy of those who have reason to remove ceiling tiles
Access to utilities and additional storage space are two reasons to remove tiles.

100. Fire Codes Require fire-rated assemblies be maintained
Replacement acoustical tile may be combustible.
All penetrations of the ceiling must be rated as part of the ceiling system.

101. Term Fire Rated
Used quite often in the fire protection and building construction fields
Nonspecific and meaningless
No part of a listed fire-resistance system stands by itself.

102. Integrity of a Ceiling System
Most are unaware of its significance.
Alterations compromise integrity.
Tiles are replaced haphazardly.
Holes are cut through tiles.
Displays are hung from the metal grid.

103. Laboratory Fire Tests
Conducted under a slight negative pressure to remove smoke and fumes
Fires generate positive pressure, and lay-in ceiling tiles may be easily displaced by fire pressures.

104. Addition of Insulation
Might not be part of the specifications of the listed ceiling assembly
Wrong insulation causes heat to be held in the channels supporting the tiles.
A membrane protection system must be perfect.

105. Cockloft Occurs between the ceiling and floor
Allows for rapid fire spread
Case example:
Fire starting in one room traveled across a hallway above the ceiling.
It came down through the tile ceiling of another room to ignite books.

106. Firestopping Some code provisions provide for this.
Use of plenum space for various services makes it probable that the firestopping will conform only to the definition of legal firestopping.

107. Deep, Long-Span Trusses
In some buildings, used to provide clear floor areas
Creates plenum spaces several feet in height
Sometimes voids are called “interstitial spaces.”
Using such space as storage places fire load next to unprotected steel.

108. Fire Resistance of Floor–Ceiling Assemblies
Not all are intended to be fire resistive.
A steel bar-joist floor with concrete topping and flame-spread-rated tiles below may appear to be fire resistive, but it is not.

109. Missing Tiles
Does not necessarily mean that a fire resistance system has been violated
The building may be of noncombustible construction.
In such a case, ceiling tiles are at the option of the owner.

110. Concrete Construction Building
Some concrete assemblies have suspended tiles incorporated.
Most of the time, the suspended ceiling is installed to provide a hidden void for utilities.

111. Fireproofing and Building Codes
Applied to meet the standards required by the local building code
Local building department will indicate which systems tested at which laboratories are acceptable.

112. Efficiency of Fireproofing
Depends on the competence of the subcontractor
Also depends on the building department staff and on the fire department inspectors

113. Encasement Methods Terra-cotta tile Early method for encasement
Case example:
The cast-iron columns of the Parker Building in New York City were protected with 3-inch terra-cotta tiles, but still burned and failed.

114. Errors in Encasement Leaving the bottom web of beams unprotected
Skewbacks, which are tiles shaped to fit around steel, correct this error.
Skewbacks, however, often are removed for other reasons.

115. Limitations of Encasement Method
Fireproofing that is easily removed is a hazard.
Case example:
A contractor removed the fireproofing protection from a major column.
About a hundred cylinders of propane gas were stored adjacent to the column.

116. Concrete Encasement
Concrete became quite popular as a protective covering for steel.
Wood falsework provides a high fuel load.
Has been involved in a number of serious construction fires

117. Fireproofing of Steel and Concrete Beams
Fireproofing is integral.
Accomplished by a specified mix of concrete in a specified thickness
Some concrete is necessary for fireproofing.

118. Disadvantage of Concrete
It is heavy.
Fireproofing is often a tempting target for cutting back.
Wire lath covered with cement plaster and gypsum have been used for fireproofing for many years.
Both lighter than concrete.

119. Sprayed-on Fireproofing
Sprayed concrete spalls badly when exposed to fire.
Other sprayed-on fireproofing can pass laboratory tests, but questions exist about their reliability in the field.

120. Issues with Sprayed-on Material
Importance not understood by other trades
Case example: A building with fireproofing stripped from the columns by plasterers

121. Issues with Sprayed-on Material
Importance not understood (cont’d)
Case example: A state office building in California had poorly applied fireproofing material.
If properly applied, can be very effective
Case example: First Interstate Bank of Los Angeles

122. Asbestos Fiber Fireproofing
Serious health hazard in its use
Difficult to sell a building with asbestos fireproofing
Asbestos is being removed from existing buildings.

123. Signs of Trouble Deteriorated concrete
Spalling that exposes reinforcing rods
Cracks in concrete

124. Chemical Processes Fumes can damage or destroy concrete.
West Roxbury, MA, swimming pool roof collapse
Aluminum reacts with concrete.

125. Parking Garages
When salt is used to melt snow and ice, corrosion is prevalent.
Damage is often difficult to determine.

126. Calcium Chloride Added to concrete Has caused problems
Preventive measures include:
Sealing the concrete
Providing adequate drainage
Flushing surfaces with fresh water in the spring

127. Concrete Rehabilitation
Includes removal and replacement
Installation of cathodic protection
Using additional steel beams

128. Unprotected Steel Concrete structures
Often repaired with steel
Steel cables fail even below 800˚F.

129. Unprotected Steel Fire fighters’ role
Should watch what is being done to buildings
Almost none of what is done to a building after it is completed benefits the fire suppression effort.

130. Unprotected Steel Fire fighters’ role (cont’d) Case example:
Fire fighter student saw structural problem with mall roof.
Owner did not want building department to know of problem.

131. Unprotected Steel Steel designed into the structure
Proper degree of fireproofing is usually specified.
If it is not designed into a structure, it is usually unprotected.

132. Ceiling Finish and Voids
Concrete construction has no inherent voids.
Finish stages of the building can create voids.

133. Waffle Slab Concrete
Imitation plastic waffle concrete is often suspended below the structural slab.
Problem: Combustible tile with a high fire-hazard rating is often used for ceilings.
Interconnected voids make it possible for the tile to burn on both sides.

134. Suspended Ceilings
When installed as part of initial construction, more likely to have satisfactory fire hazard characteristics
Tile usually as safe as the law requires

135. Combustible Tile Need not be suspended to create a serious hazard
Flammable adhesive creates problems.
Installing new ceilings below old combustible tile ceilings presents a serious hazard.
Case example:
John Sevier Retirement Center fire

136. Combustible Voids Can be created in a variety of ways Case example:
A wooden suspended ceiling is installed in an otherwise concrete construction.
Sprinklers are below the ceiling.
Fire could burn unchecked in the void.

137. Modern Office Building
Has huge communications and other utility requirements
As much as one third of the height from floor to ceiling may be in-ceiling or under-floor voids.

138. Noncombustible Voids
Combustible thermal or electrical insulation and combustible plastic service piping may be in ceiling void.
Hung ceilings are generally not required for the structural integrity of the building.

139. The Integrity of Floors
In fire-resistive buildings
Floor will be a barrier to the extension of fire.
More codes are requiring sprinkler protection.
Compartmentation is rarely achieved.

140. Building Use Requires that floor be penetrated
Often, such penetrations compromise the integrity of the floor.

141. Enclosures Around Ducts
May be inadequate
Can permit transmission of fire and/or smoke to other floors
Poke-throughs are holes provided to draw utility services up to a floor from the void below.

142. Penetrations of Floors for Services
Are increasing
Floor may be unable to resist the passage of fire adequately.
Suspended ceiling hopefully will develop the necessary fire resistance.
Owner is not free to modify the ceiling.

143. Concrete Floors Require expansion joints Case examples:
Steel expansion joints transmitted fire from floor to floor in a huge postal building.
Molten aluminum expansion joints extended fire at McCormick place.
Concrete shrinks and creates cracks, which allows fire to pass.

144. Imitation Materials Imitation concrete panels
Commonly used, particularly on the exterior of buildings
Fasteners that hold the panels on the building are made of plastic.
If the plastic burns or melts, the panels will drop off the building.

145. Energy Conservation
Has brought about the use of exterior insulation and finish systems (EIFS)
Buildings can be finished in this manner when constructed or modified later.
Case example:
Fort Worth, Texas, courthouse

146. Concrete’s Behavior in Fire
Concrete in fire-resistive construction
Resists compressive stresses
Protects the tensile strength of steel from fire
By sacrificing itself, the concrete provides time to extinguish a fire.

147. Impact Loads Will damage concrete
When spoiling has reached reinforcing steel, shoring should be done.
Concrete floors may give no clue to the distress on the other side.

148. Cutting Tensioned Concrete
Fire tactics
Can include cutting through a concrete floor for accessibility
Hole cutter can cut a hole in conventional reinforced concrete and reinforcing rods.

149. Cutting Tensioned Concrete
Tensioned concrete structures
Steel cables are under tremendous tension.
Cutting tension cables creates a potential whip.

150. Precast Concrete Cast-in-place, monolithic concrete buildings
Resistant to collapse
The loss of a column does not necessarily cause collapse.
Load will be redistributed.

151. Precast Concrete Precast concrete buildings
Individual columns, floors, girders, and wall panels are pinned by connectors.
No protective covering is provided for the connectors.
Fire load must be severe to cause failure.

152. Explosions in a Precast, Pinned Building
None of the redundancies of a rigid-framed monolithic concrete building
Case example:
Ronan Point collapse
© EMPICS/Landov

153. Concrete Trusses Not common
Exist in the Tampa, Florida, and Dallas/Fort Worth, Texas, airports
Exist in the American Airlines hangar at Dallas/Fort Worth
Courtesy of Glenn Corbett.

154. Fires in Type I Buildings: Case Example 1
Los Angeles Central Library Fire in 1986
Loss was immense.
200,000 books and numerous periodical collections were destroyed.
The book stacks provided an estimated 93 pounds per square foot (psf) of fuel.

155. Fires in Type I Buildings: Case Example 2
High-rise apartment building in Dallas, Texas
Christmas tree fire
$340,000 in damage
Utility and vent pipes had been punched through the ceilings.

156. Fires in Type I Buildings: Case Example 3
Military Records Center near St. Louis, MO, in 1973
The fire load included over 21 million military personnel files in cardboard boxes on metal shelves.

157. Signs of Potential Collapse in Type I Construction
Variety of problems can cause collapse.
Signs are not always clear.

158. Conditions for Anticipating Collapse
Knowledge of problematic existing building conditions
Dangerous loads
Cutting tensioned cables
Heavy fire conditions over an extended period of time

159. Know Your Buildings
When building rate is high, difficult for fire departments to keep pace
Slowdowns present an opportunity to get current on the hazards of specific buildings.
“Experience keeps a dear school, but fools will learn in no other.”

160. Summary
Concrete is a cementatious material produced by a chemical reaction.
There are two basic types of in-concrete construction: cast-in-place concrete and precast concrete.
Prestressing places engineered stresses in architectural and structural concrete.

161. Summary
Concrete buildings under construction can present serious fire problems.
When concrete construction was first developed, was believed to be truly fireproof.
After a series of disastrous fires it became evident that concrete can be destroyed by fire given sufficient fire load and fire duration.

162. Summary
Clear signs of possible trouble can be determined in a prefire plan.
Type I construction lacks inherent voids.
The concrete in fire-resistive construction serves two purposes—it resists compressive stresses and protects the tensile strength of steel from fire.
By sacrificing itself, the concrete provides time to extinguish the fire.