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Ch 10 Fire-Resistive Construction


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Ch 10 Fire-Resistive Construction

  1. 1. 10 Fire-Resistive Construction
  2. 2. Objectives (1 of 2)‏ <ul><li>Recall the difference between noncombustible and fire-resistive construction </li></ul><ul><li>Describe different types of concrete structural systems </li></ul><ul><li>Describe the two types of prestressing </li></ul>10
  3. 3. Objectives (2 of 2)‏ <ul><li>Contrast precast and site-cast concrete </li></ul><ul><li>Describe the hazards of formwork </li></ul><ul><li>Describe the methods of fireproofing steel and of ensuring a level fire resistance in concrete </li></ul><ul><li>Detail how compartmentation works to prevent the spread of fire </li></ul>10
  4. 4. Introduction <ul><li>Fire-resistive construction </li></ul><ul><ul><li>Considered to be the best </li></ul></ul><ul><ul><li>Most resistant to collapse and does not contribute fuel to a fire </li></ul></ul><ul><ul><li>Is given the largest permissible area and heights </li></ul></ul>10
  5. 5. Concrete <ul><li>Cementatious material produced by a chemical reaction </li></ul><ul><li>Cures indefinitely; low temperatures retard the curing of concrete </li></ul><ul><li>Weak in tensile strength and has poor shear resistance </li></ul>10
  6. 6. Concrete Structures Pre-World War II <ul><li>Suitable only for structures in which aesthetics played little part </li></ul><ul><li>Built of steel frames and fireproofed with concrete </li></ul><ul><li>Cinder blocks use cinders as the aggregate </li></ul><ul><li>Concrete blocks use other materials for aggregate </li></ul>10
  7. 7. Underwriters Blocks <ul><li>Concrete blocks produced under Underwriters Laboratories’ classification </li></ul><ul><li>Manufacturer’s certificate gives the type and number of units delivered to a specific job </li></ul><ul><li>Blocks must meet fire resistance standards </li></ul>10
  8. 8. Today’s Variety of Concrete Structures <ul><li>Use variety of building construction elements </li></ul><ul><li>Steel-framed buildings now often have cast-in-place concrete floors </li></ul><ul><li>Precast concrete and prefabricated metal wall panels and decorative brick veneer are common </li></ul>10
  9. 9. Steel vs. Concrete Framing <ul><li>Designer preferences </li></ul><ul><ul><li>Some design in steel </li></ul></ul><ul><ul><li>Others prefer concrete </li></ul></ul><ul><ul><li>Some buildings concrete-framed and steel-framed mixed together </li></ul></ul>10
  10. 10. Fire Department Problems <ul><li>Problems with concrete construction </li></ul><ul><ul><li>Collapse during construction with no fire </li></ul></ul><ul><ul><li>Fire during construction </li></ul></ul><ul><ul><li>Fire in completed, occupied buildings </li></ul></ul>10
  11. 11. Types of Concrete Construction <ul><li>Cast-in-place </li></ul><ul><ul><li>Plain, reinforced, and post-tensioned concrete </li></ul></ul><ul><li>Precast </li></ul><ul><ul><li>Plain, reinforced, and pretension concrete </li></ul></ul>10
  12. 12. Concrete Definitions (1 of 5)‏ <ul><li>Aggregate </li></ul><ul><li>Cast-in-place concrete </li></ul><ul><li>Casting </li></ul><ul><li>Chairs </li></ul><ul><li>Composite and combination columns </li></ul>10
  13. 13. Concrete Definitions (2 of 5)‏ <ul><li>Composite construction </li></ul><ul><li>Continuous casting </li></ul><ul><li>Continuous slipforming </li></ul><ul><li>Drop panels </li></ul><ul><li>Flat plate structural system (or continuous beam)‏ </li></ul>10
  14. 14. Concrete Definitions (3 of 5)‏ <ul><li>Footings </li></ul><ul><li>Lally columns </li></ul><ul><li>Lift slab </li></ul><ul><li>Monolithic construction </li></ul><ul><li>Mushroom caps </li></ul>10
  15. 15. Concrete Definitions (4 of 5)‏ <ul><li>One-way structural system </li></ul><ul><li>Plain concrete </li></ul><ul><li>Pretensioning and post-tensioning </li></ul><ul><li>Precast concrete </li></ul><ul><li>Reinforced concrete </li></ul><ul><li>Reinforcing bars or rods </li></ul>10
  16. 16. Concrete Definitions (5 of 5)‏ <ul><li>Slipforming </li></ul><ul><li>Spalling </li></ul><ul><li>Temperature rods </li></ul><ul><li>Two-way structural system </li></ul>10
  17. 17. Concrete Structural Elements <ul><li>Columns </li></ul><ul><li>Beams (including t-beams) and girders </li></ul><ul><li>Concrete floors </li></ul>10
  18. 18. Virtue of Columns <ul><li>High compressive strength and low cost </li></ul><ul><li>Columns are of reinforced concrete </li></ul><ul><li>Steel reinforcing rods carry some of the compressive load </li></ul><ul><li>The compressive strength of steel is many times that of concrete </li></ul>10
  19. 19. Increasing Column Sizes <ul><li>Unsatisfactory in modern construction </li></ul><ul><li>The useable area would vary from floor to floor </li></ul><ul><li>Overcome by increasing the size of the reinforcing steel as the loads increase </li></ul>10
  20. 20. Reinforcing Rods <ul><li>Long with a relatively thin diameter </li></ul><ul><li>Ends of rods are connected </li></ul><ul><li>Ties or hoops join the rods in a column </li></ul><ul><li>Ties cut the long slender column into a number of relatively short columns </li></ul>10
  21. 21. Beams and Girding (1 of 3) ‏ <ul><li>Plain concrete beam </li></ul><ul><ul><li>Strong in compression, weak in shear </li></ul></ul><ul><ul><li>No tensile strength </li></ul></ul><ul><ul><li>When a beam is loaded, it deflects </li></ul></ul><ul><ul><li>Deflection brings compression in the top of the beam and tension in the bottom of the beam </li></ul></ul>10
  22. 22. Beams and Girding (2 of 3)‏ <ul><li>Cantilever beam </li></ul><ul><ul><li>Tension is in the top of the beam </li></ul></ul><ul><ul><li>Reinforcing rods are in the top of the beam </li></ul></ul>10
  23. 23. Beams and Girding (3 of 3)‏ <ul><li>Continuous beam </li></ul><ul><ul><li>Supported at more than two points </li></ul></ul><ul><ul><li>Tension in the top of the beam in the area over the tops of the columns </li></ul></ul><ul><ul><li>Tension in the bottom of the beams between columns </li></ul></ul>10
  24. 24. T-Beams <ul><li>There is neither tension nor compression in the beam </li></ul><ul><li>Has the neutral plane coincide with the bottom of the wide, thin floor slab </li></ul><ul><li>Double T’s are floor slab and beam combinations with two beams </li></ul>10
  25. 25. Concrete Floors <ul><li>First used for leveling brick and tile arch floors </li></ul><ul><li>Early floors built of individual beams supporting a floor slab </li></ul><ul><li>Hollow tiles lightened concrete floors </li></ul>10
  26. 26. Waffle Concrete <ul><li>Closely spaced beams are set at right angles to one another </li></ul><ul><li>Unnecessary concrete is formed out </li></ul>10
  27. 27. Lighter Construction <ul><li>Floor may be just a flat plate </li></ul><ul><li>This gives a smooth surface </li></ul><ul><li>Easily finished </li></ul>10
  28. 28. Left-In-Place Form <ul><li>Occurs when concrete floors are cast onto corrugated steel </li></ul><ul><li>The steel provides necessary tensile strength </li></ul><ul><li>If the bond fails, the floor section may fail </li></ul>10
  29. 29. Precast T-Beam Units <ul><li>Additional concrete is often cast-in-place on top of the units </li></ul><ul><li>Entire unit becomes an integral beam-and-floor element </li></ul><ul><li>Cylindrical openings can be cast lengthwise through the units to remove unnecessary weight </li></ul>10
  30. 30. Older Building Codes <ul><li>Concrete floor can be in ordinary construction </li></ul><ul><li>Case example: Concrete topping over wood beams concealed the destruction of the beams by fire. Four fire fighters died </li></ul>10
  31. 31. One-Hour-Rated Designs of Wood Floors <ul><li>Lightweight concrete topping as much as 1 to 1 1/2 inches thick </li></ul><ul><li>Thickness retards the passage of heat through the floor </li></ul><ul><li>National Fire Protection Association (NFPA) 251 (American Society of Testing and Materials (ASTM) E119) fire resistance standard </li></ul>10
  32. 32. Cast-In-Place Concrete Floor <ul><li>Can be a hazard during construction </li></ul><ul><li>A slot is left in the wall at the point where the floor is to be cast </li></ul><ul><li>If a windstorm occurs during the time that the slot is open, a collapse may result </li></ul>10
  33. 33. Concrete Floors in Steel Buildings <ul><li>May be precast or cast-in-place </li></ul><ul><li>May be only load-bearing or provide structural stability </li></ul>10
  34. 34. Concrete Floors in Cast-In-Place, Concrete-Framed Buildings <ul><li>Cast integrally with columns </li></ul><ul><li>Provide a monolithic rigid-framed building </li></ul><ul><li>May be pinned </li></ul><ul><li>May be connected as a monolithic unit </li></ul>10
  35. 35. When Slabs Are Laid Down <ul><li>A space is left between them </li></ul><ul><li>Protruding bars of one slab extend past the ends of the protruding bars of the other slab </li></ul><ul><li>The sections are joined by a wet joint </li></ul>10
  36. 36. Concrete Floors in Precast, Pinned Concrete Buildings <ul><li>May not contribute to the building’s structural stability </li></ul><ul><li>Precast columns are often built with haunches or shelves </li></ul><ul><li>Steel plates imbedded in the concrete may be welded together </li></ul>10
  37. 37. Prestressed Concrete <ul><li>Recently developed </li></ul><ul><li>Engineered stresses placed in architectural and structural concrete </li></ul><ul><li>Analogy: A row of books side by side, before and after being threaded together with wire </li></ul>10
  38. 38. Special High-Strength, Cold-Drawn Steel Cables <ul><li>Similar to those used for suspension bridges </li></ul><ul><li>These or alloy steel bars are commonly used in prestressed concrete </li></ul><ul><li>Known as tendons, but also called strands or cables </li></ul>10
  39. 39. High-Tensile-Strength Wire <ul><li>Ordinarily used for prestressing </li></ul><ul><li>More sensitive to high temperatures than structural steel </li></ul><ul><li>Complete loss of prestress at 800°F </li></ul>10
  40. 40. Two Methods of Prestressing (1 of 2)‏ <ul><li>Pretensioning </li></ul><ul><ul><li>Done in a plant </li></ul></ul><ul><ul><li>High-tensile-strength steel strands are stretched between the ends of a form </li></ul></ul><ul><ul><li>After processing, stretched strands draw back, thus compressing the concrete </li></ul></ul>10
  41. 41. Two Methods of Prestressing (2 of 2)‏ <ul><li>Post-tensioning </li></ul><ul><ul><li>Done on the job site </li></ul></ul><ul><ul><li>High-tensile-steel strand wires are positioned in the forms </li></ul></ul><ul><ul><li>After processing, steel tendons are stretched and anchored at the ends of the unit </li></ul></ul>10
  42. 42. Bridge Girders <ul><li>Some are tensioned enough to make shipment possible, then post-tensioned after being placed </li></ul><ul><li>Cement paste might be forced into the space between the tendon and the concrete to provide a bond </li></ul>10
  43. 43. Reinforced Masonry <ul><li>Widely used to resist earthquakes </li></ul><ul><li>Unsuitable for multistory buildings in which large clear spans are required </li></ul><ul><li>Apartment houses and motels are well adapted to this method </li></ul>10
  44. 44. Ordinary Brick Bearing-Wall Buildings (1 of 2)‏ <ul><li>Walls must increase in thickness as the building’s height increases. </li></ul><ul><li>Limit is generally about 6 stories </li></ul><ul><li>Recent years, possible to 20 or more stories </li></ul>10
  45. 45. Ordinary Brick Bearing-Wall Buildings (2 of 2)‏ <ul><li>Construction methods allow higher buildings </li></ul><ul><ul><li>Two wythes of brick are built </li></ul></ul><ul><ul><li>The width of one brick is left between them </li></ul></ul><ul><ul><li>Reinforcing rods are placed vertically </li></ul></ul><ul><ul><li>Concrete is poured into the void </li></ul></ul>10
  46. 46. Special Cases (1 of 2)‏ <ul><li>Low-rise buildings </li></ul><ul><ul><li>Recent designs have eliminated reinforced concrete in the wall </li></ul></ul><ul><ul><li>High compressive-strength bricks and special mortar are used instead </li></ul></ul><ul><ul><li>Masonry wall-bearing building can be several stories high </li></ul></ul>10
  47. 47. Special Cases (2 of 2) ‏ <ul><li>Concrete block </li></ul><ul><ul><li>Has become popular for some resorts </li></ul></ul><ul><ul><li>With outside open-air stairways and balconies, life safety is achieved </li></ul></ul>10
  48. 48. Collapse Under Construction <ul><li>Concrete structures under construction sometimes collapse </li></ul><ul><li>Fire department rescues construction workers </li></ul><ul><li>Fire officers should be well informed on the legal position of the fire department </li></ul>10
  49. 49. Ordering the Removal of a Dangerous Structure <ul><li>Power given to the building commissioner </li></ul><ul><li>Fire department has no right to demolish such a structure. </li></ul>10
  50. 50. Lawsuits <ul><li>Common today </li></ul><ul><li>Owner, architect, general contractor, subcontractors, and victims attempt to determine financial responsibility </li></ul><ul><li>After collapses, some of those involved may try to cover up their actions </li></ul>10
  51. 51. An Industry Warning <ul><li>Experts have warned of the collapse hazard of concrete structures </li></ul><ul><li>Design engineers should use construction loads as governing loads in structures </li></ul>10
  52. 52. Problems of Falsework <ul><li>Falsework </li></ul><ul><ul><li>Temporary structure to support concrete work in the course of construction </li></ul></ul><ul><ul><li>Can represent 60% of the cost of a concrete structure </li></ul></ul>10
  53. 53. Concrete Formwork <ul><li>Designed without the extra strength calculated into a building to compensate for deterioration </li></ul><ul><li>Built at the lowest possible cost </li></ul><ul><li>Formwork failures can occur, but it is surprising is that they are relatively rare </li></ul>10
  54. 54. Falsework for Walls or Columns <ul><li>Must have adequate strength to resist the pressure of heavy fluid concrete </li></ul><ul><li>As concrete sets, pressure is reduced due to internal friction </li></ul><ul><li>Setting of concrete is temperature dependent </li></ul>10
  55. 55. Reshoring Concrete <ul><li>Concrete requires time to cure </li></ul><ul><li>Formwork is then removed </li></ul><ul><li>Reshoring is putting shores back in place to help carry the load </li></ul><ul><li>Reshoring means concrete is not yet set </li></ul>10
  56. 56. Collapses of Floors (1 of 2)‏ <ul><li>Many involve formwork supporting newly cast or high bay floors </li></ul><ul><li>Proper cross-bracing can help prevent this </li></ul>10
  57. 57. Collapses of Floors (2 of 2)‏ <ul><li>Formwork can also be a problem </li></ul><ul><ul><li>Often rests on the ground </li></ul></ul><ul><ul><li>Mudsills are the planks on which the shores rest </li></ul></ul><ul><ul><li>If mud is involved, bearing may be inadequate </li></ul></ul>10
  58. 58. A Widely Believed Fallacy <ul><li>“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.” </li></ul>10
  59. 59. Skyline Towers Collapse <ul><li>Skyline Towers collapsed in Arlington, Virginia, 1973 </li></ul><ul><li>Collapse proved the fallacy </li></ul><ul><li>Shoring had been removed from the topmost floor </li></ul><ul><li>The floor collapsed, and the collapse was progressive </li></ul>10
  60. 60. Lessons from Skyline Towers <ul><li>Removal of shoring by laborers is no different than removal by fire </li></ul><ul><li>Any concrete formwork failure presents the likelihood for catastrophic collapse </li></ul><ul><li>Few concrete buildings can withstand the collapse of one floor onto another </li></ul>10
  61. 61. Hazards of Post-Tensioning (1 of 2)‏ <ul><li>Hydraulic jacks are used to tension the tendons or jack the cables </li></ul><ul><li>No bond between the tendons and the concrete </li></ul>10
  62. 62. Hazards of Post-Tensioning (2 of 2)‏ <ul><li>Weight of concrete transfers to columns only when tensioning is complete </li></ul><ul><li>Case example: The Skyline Towers garage was made of post-tensioned concrete. Poor sheer resistance led to collapse </li></ul>10
  63. 63. Collapse of Reinforced Masonry <ul><li>Used widely in construction </li></ul><ul><li>Workers might overload a floor portion </li></ul><ul><li>Case example: In Pittsburgh, Pennsylvania an excess load caused the partial collapse of several stories of precast floors </li></ul>10
  64. 64. Collapse of Precast Concrete <ul><li>Precast concrete buildings under construction are unstable </li></ul><ul><li>Temporary bracing holds units in place </li></ul><ul><li>Wooden temporary shoring might also be used </li></ul><ul><li>Case example: Montgomery County Maryland. Three-story garage collapsed due to oversized washer </li></ul>10
  65. 65. Lift-slab Collapses (1 of 3)‏ <ul><li>Lift-slab construction </li></ul><ul><ul><li>Ground floor slab is cast first </li></ul></ul><ul><ul><li>Bond breakers are used between the slabs </li></ul></ul><ul><ul><li>Slabs are raised to the columns </li></ul></ul><ul><ul><li>Each floor is temporarily connected to the columns </li></ul></ul>10
  66. 66. Lift-Slab Collapses (2 of 3)‏ <ul><li>Case example: L’Ambience Plaza concrete building under construction in Connecticut was due to the failure of a single connection </li></ul>10
  67. 67. Lift-Slab Collapses (3 of 3)‏ <ul><li>When do the accidents occur? </li></ul><ul><ul><li>While the slabs are being lifted or while no lifting is being done </li></ul></ul><ul><li>Case example: In California, a roof slab was lifted to columns three inches out of plumb. As an attempt was made to pull the slab back into place, it collapsed </li></ul>10
  68. 68. Fire Problems of Concrete Buildings Under Construction <ul><li>Concrete buildings under construction can present serious fire problems </li></ul><ul><li>Fire in formwork can easily result in major collapse </li></ul><ul><li>Little reserve strength in formwork </li></ul><ul><li>Little understanding of potential hazard </li></ul>10
  69. 69. Potential Fires at a Construction Site <ul><li>Fires at a construction site </li></ul><ul><ul><li>Causes include welding, cutting, and plumbers’ torches; temporary electrical lines; and arson </li></ul></ul><ul><ul><li>Fuels are readily available </li></ul></ul><ul><ul><li>Glass-fiber formwork is also combustible </li></ul></ul>10
  70. 70. Hazard of Heating <ul><li>Burning of scrap wood in steel barrels or the use kerosene heaters are hazards </li></ul><ul><li>Liquefied petroleum gas (LPG) is also dangerous </li></ul>10
  71. 71. Codes for LPG (1 of 2)‏ <ul><li>Store gas away from any open flames. </li></ul><ul><ul><li>Case example: 1963, LPG explosion at the Indianapolis Coliseum; caused when a leaking gas-fired cooker cylinder exploded and gas reached heater flame </li></ul></ul>10
  72. 72. Codes for LPG (2 of 2)‏ <ul><li>Install excess flow valves. </li></ul><ul><ul><li>Case example: In one city, gas stored and piped with plastic tubes at ground level; hazard should line break </li></ul></ul>10
  73. 73. Hazards of Post-Tensioned Concrete (1 of 2)‏ <ul><li>Catastrophic fire collapse potential </li></ul><ul><li>Include bridges and parking garages </li></ul><ul><li>Falsework fire could cause the sudden collapse of an entire concrete floor slab </li></ul><ul><li>After tensioning, the ends of tendons are left exposed </li></ul>10
  74. 74. Hazards of Post-Tensioned Concrete (2 of 2)‏ <ul><li>Hanging tendons can fail at about 800°F </li></ul><ul><li>Excess tendons are rolled up and attached to a wooden rack. </li></ul><ul><li>Rolled-up tendons are heat collectors </li></ul><ul><li>Failure of tendons will cause the collapse of that part of the structure </li></ul>10
  75. 75. Protection of Tendons <ul><li>Insist on fireproofing tendon anchors immediately after tensioning is completed </li></ul><ul><li>Insist on temporary protection for incrementally tensioned tendons </li></ul>10
  76. 76. A Total Collapse: Case Example <ul><li>A post-tensioned building under construction in Cleveland, Ohio, suffered a falsework fire </li></ul><ul><li>After a second fire, the entire 18-story building collapsed </li></ul>10
  77. 77. Precast Buildings (2 of 2)‏ <ul><li>Pose unique hazards while being constructed </li></ul><ul><li>Construction involves erection of precast concrete units. </li></ul>10
  78. 78. Precast Buildings (2 of 2)‏ <ul><ul><li>Temporary bracing or support is used; it can collapse </li></ul></ul><ul><ul><li>Columns can be braced with wood rather than by telescoping tubular steel braces; wood is flammable </li></ul></ul><ul><ul><li>Cold-drawn steel cables often provide diagonal bracing in precast buildings; these fail at 800° F </li></ul></ul>10
  79. 79. Cantilevered Platforms <ul><li>Used by cranes delivering materials to buildings under construction </li></ul><ul><li>Are braced by wooden shores that would fail in a fire </li></ul>10
  80. 80. Tower Cranes <ul><li>Supported on the building’s structural frame </li></ul><ul><li>Weight of the crane may be distributed over several floors by falsework </li></ul><ul><li>A fire involving this falsework can bring down the crane </li></ul>10
  81. 81. Falsework on a Completed Floor <ul><li>Should be investigated </li></ul><ul><li>May be supporting a patch over a hole </li></ul><ul><li>May be supporting a heavy load such as the crane </li></ul>10
  82. 82. Falsework: Case Example <ul><li>Formwork for concrete placement burned on the 23 rd to 25 th floors of a high-rise </li></ul><ul><li>Operator was trapped in his cab </li></ul><ul><li>He was protected with a heavy-caliber stream from a nearby roof until rescued </li></ul>10
  83. 83. Fire Problems in Finished Buildings <ul><li>Concrete construction </li></ul><ul><ul><li>Thought to be truly fireproof </li></ul></ul><ul><ul><li>Later, it was learned that concrete, like any other noncombustible material, can be destroyed by fire </li></ul></ul>10
  84. 84. Characteristics of Concrete <ul><li>Inherently noncombustible </li></ul><ul><li>Some people confuse noncombustibility with fire resistance </li></ul><ul><li>Neither is synonymous with fire safety </li></ul>10
  85. 85. Safety of Concrete Construction: Case Example <ul><li>Reinforced concrete Joelma building in Sao Paulo, Brazil, burned in 1974 </li></ul><ul><li>Resulted in179 deaths. The structure had minor damage. </li></ul>10
  86. 86. Fireproofing (Insulating) Steel <ul><li>Has a fire resistance rating if the protection system previously passed a standard fire test </li></ul><ul><li>No such thing as a truly fireproof building </li></ul><ul><li>Fireproofed steel is protected steel </li></ul>10
  87. 87. Types of Fireproofing (1 of 2)‏ <ul><li>Individual fireproofing provides protection for each piece of steel </li></ul><ul><li>Methods include encasement and intumescent coating </li></ul><ul><li>Membrane fireproofing does not protect individual members </li></ul>10
  88. 88. Types of Fireproofing (2 of 2)‏ <ul><li>One method uses a rated floor-ceiling assembly </li></ul><ul><li>Underwriters Laboratories can test a roof and ceiling assembly </li></ul><ul><li>NFPA 251 (ASTM E119) standard fire test </li></ul>10
  89. 89. Hazards of Floor–ceiling Assemblies <ul><li>Can present a serious menace to the safety of fire fighters </li></ul><ul><li>Assemblies need to be assembled exactly as performed in the laboratory </li></ul>10
  90. 90. Ceiling System <ul><li>At the mercy of those have reason to remove ceiling tiles </li></ul><ul><li>Access to utilities and additional storage space are two reasons to remove tiles </li></ul>10
  91. 91. Legal Provisions <ul><li>None require membrane protection be maintained </li></ul><ul><li>Replacement acoustical tile may be combustible </li></ul><ul><li>All penetrations of the ceiling must be rated as part of the ceiling system </li></ul>10
  92. 92. Term “Fire-rated” <ul><li>Used quite often in the fire protection and building construction fields </li></ul><ul><li>Nonspecific and meaningless </li></ul><ul><li>No part of a listed fire-resistance system stands by itself </li></ul>10
  93. 93. Integrity of a Ceiling System <ul><li>Most are unaware of its significance </li></ul><ul><li>Alterations compromise integrity </li></ul><ul><ul><li>Tiles are replaced haphazardly </li></ul></ul><ul><ul><li>Holes are cut through tiles </li></ul></ul><ul><ul><li>Displays are hung from the metal grid </li></ul></ul><ul><li>Testing doesn’t include superimposed loads </li></ul>10
  94. 94. Laboratory Fire Tests <ul><li>Conducted under a slight negative pressure to remove smoke and fumes </li></ul><ul><li>Fires generate positive pressure, and lay-in ceiling tiles may be easily displaced by fire pressures </li></ul>10
  95. 95. Addition of Insulation <ul><li>Might not be part of the specifications of the listed ceiling assembly </li></ul><ul><li>Wrong insulation causes heat to be held in the channels supporting the tiles </li></ul><ul><li>A membrane protection system must be perfect </li></ul>10
  96. 96. Cockloft <ul><li>Occurs between the ceiling and floor </li></ul><ul><li>Allows for rapid fire spread </li></ul><ul><li>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 </li></ul>10
  97. 97. Firestopping <ul><li>Some code provisions provide for this </li></ul><ul><li>Use of plenum space for various services makes it probable that the firestopping will conform only to the definition of legal firestopping </li></ul>10
  98. 98. Deep, Long-span Trusses <ul><li>In some buildings, used to provide clear floor areas </li></ul><ul><li>This creates plenum spaces several feet in height </li></ul><ul><li>Sometimes voids are called “interstitial spaces” </li></ul><ul><li>Using such space as storage places fire load next to unprotected steel </li></ul>10
  99. 99. Fire Resistance of Floor-Ceiling Assemblies <ul><li>Not all are intended to be fire resistive </li></ul><ul><li>A steel bar-joist floor with concrete topping and flame-spread-rated tiles below may appear to be fire resistive, but it is not </li></ul>10
  100. 100. Missing Tiles <ul><li>Does not necessarily mean that a fire resistance system has been violated </li></ul><ul><li>The building may be of noncombustible construction </li></ul><ul><li>In such a case, ceiling tiles are at the option of the owner </li></ul>10
  101. 101. Concrete Construction Building <ul><li>Some concrete assemblies have suspended tiles incorporated </li></ul><ul><li>Most of the time, the suspended ceiling is installed to provide a hidden void for utilities </li></ul>10
  102. 102. Fireproofing and Building Codes <ul><li>Fireproofing </li></ul><ul><ul><li>Applied to meet the standards required by the local building code </li></ul></ul><ul><ul><li>Further, building department will indicate which systems tested at which laboratories are acceptable. </li></ul></ul>10
  103. 103. Efficiency of Fireproofing <ul><li>Depends on the competence of the subcontractor </li></ul><ul><li>Also depends on the building department staff and on the fire department inspectors </li></ul>10
  104. 104. Encasement Methods <ul><li>Terra cotta tile </li></ul><ul><ul><li>Early method for encasement </li></ul></ul><ul><ul><li>Case example: The cast-iron columns of the Parker Building in New York City were protected with three-inch terra cotta tiles, but still burned and failed </li></ul></ul>10
  105. 105. Errors in Encasement <ul><li>Leaving the bottom web of beams unprotected </li></ul><ul><li>Skewbacks, which are tiles shaped to fit around steel, corrects this error </li></ul><ul><li>Skewbacks, however, often are removed for other reasons </li></ul>10
  106. 106. Limitations of Encasement Method <ul><li>Fireproofing that is easily removed is a hazard </li></ul><ul><li>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 </li></ul>10
  107. 107. Concrete Encasement <ul><li>Concrete became quite popular as a protective covering for steel </li></ul><ul><li>Wood falsework provides a high fuel load </li></ul><ul><li>Has been involved in a number of serious construction fires </li></ul>10
  108. 108. Fireproofing of Steel and Concrete Beams <ul><li>Fireproofing is integral; accomplished by a specified mix of concrete in a specified thickness </li></ul><ul><li>Some concrete is necessary for fireproofing </li></ul>10
  109. 109. Disadvantage of Concrete <ul><li>Its weight </li></ul><ul><li>Fireproofing is often a tempting target for cutting back </li></ul><ul><li>Case example: Builders replace concrete with wire laths covered with cement plaster or gypsum, both of which are lighter </li></ul>10
  110. 110. Sprayed-on Fireproofing <ul><li>Sprayed concrete spalls badly when exposed to fire </li></ul><ul><li>Other sprayed-on fireproofing can pass laboratory tests, but questions exist about their reliability in the field </li></ul>10
  111. 111. Issues with Sprayed-on Material (1 of 2) <ul><li>Importance not understood by other trades </li></ul><ul><ul><li>Case example: A building with fireproofing stripped from the columns by plasterers </li></ul></ul>10
  112. 112. Issues with Sprayed-on Material (2 of 2) <ul><ul><li>Case example: A state office building in California had poorly applied fireproofing material </li></ul></ul><ul><li>If properly applied, can be very effective </li></ul><ul><ul><li>Case example: First Interstate Bank of Los Angeles </li></ul></ul>10
  113. 113. Asbestos Fiber Fireproofing <ul><li>Serious health hazard in its use </li></ul><ul><li>Difficult to sell a building with asbestos fireproofing </li></ul><ul><li>Asbestos is being removed from existing buildings </li></ul>10
  114. 114. Signs of Trouble <ul><li>Deteriorated concrete </li></ul><ul><li>Spalling that exposes reinforcing rods </li></ul><ul><li>Cracks in concrete </li></ul>10
  115. 115. Parking Garages <ul><li>When salt is used to melt snow and ice, corrosion is prevalent </li></ul><ul><li>Damage is often difficult to determine </li></ul>10
  116. 116. Calcium Chloride <ul><li>Added to concrete </li></ul><ul><li>Has caused problems </li></ul><ul><li>Preventive measures include sealing the concrete, providing adequate drainage, and flushing surfaces with fresh water in the spring </li></ul>10
  117. 117. Concrete Rehabilitation <ul><li>Includes removal and replacement </li></ul><ul><li>Installation of cathodic protection </li></ul><ul><li>Using additional steel beams </li></ul>10
  118. 118. Unprotected Steel (1 of 4)‏ <ul><li>Concrete structures </li></ul><ul><ul><li>Often repaired with steel </li></ul></ul><ul><li>Steel cables fail even below 800°F </li></ul>10
  119. 119. Unprotected Steel (2 of 4)‏ <ul><li>Fire fighters’ role </li></ul><ul><ul><li>Should watch what is being done to buildings </li></ul></ul><ul><ul><li>Almost none of what is done to a building after it is completed benefits the fire suppression effort </li></ul></ul>10
  120. 120. Unprotected Steel (3 of 4)‏ <ul><ul><li>Case example: Fire fighter student saw structural problem with mall roof: owner did not want building department to know of problem </li></ul></ul>10
  121. 121. Unprotected Steel (4 of 4)‏ <ul><li>Steel designed into the structure </li></ul><ul><ul><li>Proper degree of fireproofing is usually specified </li></ul></ul><ul><ul><li>If it is not designed into a structure, it is usually unprotected </li></ul></ul>10
  122. 122. Ceiling Finish and Voids <ul><li>Concrete construction has no inherent voids </li></ul><ul><li>Finish stages of the building can create voids </li></ul>10
  123. 123. Waffle Slab Concrete <ul><li>Imitation plastic waffle concrete is often suspended below the structural slab </li></ul><ul><li>Problem: Combustible tile with a high fire-hazard rating is often used for ceilings </li></ul><ul><li>Interconnected voids make it possible for the tile to burn on both sides </li></ul>10
  124. 124. Suspended Ceilings <ul><li>When installed as part of initial construction, more likely to have satisfactory fire hazard characteristics </li></ul><ul><li>Tile usually as safe as the law requires </li></ul>10
  125. 125. Combustible Tile <ul><li>Need not be suspended to create a serious hazard </li></ul><ul><li>Flammable adhesive create problems </li></ul><ul><li>Installing new ceilings below old combustible tile ceilings presents a serious hazard </li></ul><ul><li>Case example: John Sevier Retirement Center fire </li></ul>10
  126. 126. Combustible Voids <ul><li>Can be created in a variety of ways </li></ul><ul><li>Case example: A wooden suspended ceiling installed in an otherwise concrete construction. Sprinklers are below the ceiling. Fire could burn unchecked in the void </li></ul>10
  127. 127. Modern Office Building <ul><li>Has huge communications and other utility requirements </li></ul><ul><li>As much as one third of the height from floor to ceiling may be in-ceiling or under-floor voids </li></ul>10
  128. 128. Noncombustible Voids <ul><li>Combustible thermal or electrical insulation and combustible plastic service piping may be in ceiling void </li></ul><ul><li>Hung ceilings are generally not required for the structural integrity of the building </li></ul>10
  129. 129. The Integrity of Floors <ul><li>In fire-resistive buildings </li></ul><ul><ul><li>Floor will be a barrier to the extension of fire </li></ul></ul><ul><ul><li>More codes are requiring sprinkler protection </li></ul></ul><ul><ul><li>Compartmentation is rarely achieved </li></ul></ul>10
  130. 130. Building Use <ul><li>Requires floor be penetrated </li></ul><ul><li>Often, such penetrations compromise the integrity of the floor </li></ul>10
  131. 131. Enclosures Around Ducts <ul><li>May be inadequate </li></ul><ul><li>Can permit transmission of fire and/or smoke to other floors </li></ul><ul><li>Poke-throughs are holes provided to draw utility services up to a floor from the void below </li></ul>10
  132. 132. Penetrations of Floors for Services <ul><li>Are increasing </li></ul><ul><li>Floor may be unable to resist the passage of fire adequately. </li></ul><ul><li>Suspended ceiling hopefully will develop the necessary fire resistance </li></ul><ul><li>Owner is not free to modify the ceiling </li></ul>10
  133. 133. Concrete Floors <ul><li>Require expansion joints </li></ul><ul><ul><li>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 </li></ul></ul><ul><li>Concrete shrinks and creates cracks, which allows fire to pass </li></ul>10
  134. 134. Imitation Materials <ul><li>Imitation concrete panels </li></ul><ul><ul><li>Commonly used, particularly on the exterior of buildings </li></ul></ul><ul><ul><li>Fasteners that hold the panels on the building are made of plastic </li></ul></ul><ul><ul><li>If the plastic burns or melts, the panels will drop off the building </li></ul></ul>10
  135. 135. Energy Conservation <ul><li>Has brought about the use of exterior insulation and finish systems (EIFS) </li></ul><ul><li>Buildings can be finished in this manner when constructed or modified later </li></ul><ul><li>Case example: Fort Worth, Texas Courthouse </li></ul>10
  136. 136. Concrete’s Behavior in Fires <ul><li>Concrete in fire-resistive construction </li></ul><ul><ul><li>Resists compressive stresses </li></ul></ul><ul><ul><li>Protects the tensile strength of steel from fire </li></ul></ul><ul><ul><li>The concrete provides time to extinguish a fire </li></ul></ul>10
  137. 137. Impact Loads <ul><li>Will damage concrete </li></ul><ul><li>When spoiling has reached reinforcing steel, shoring should be done </li></ul><ul><li>Concrete floors may give no clue to the distress on the other side </li></ul>10
  138. 138. Cutting Tensioned Concrete (1 of 2)‏ <ul><li>Fire tactics </li></ul><ul><ul><li>Can include cutting through a concrete floor for accessibility </li></ul></ul><ul><ul><li>Hole cutter can cut a hole in conventional reinforced concrete and reinforcing rods </li></ul></ul>10
  139. 139. Cutting Tensioned Concrete (2 of 2)‏ <ul><li>Tensioned concrete structures </li></ul><ul><ul><li>Steel cables are under tremendous tension </li></ul></ul><ul><ul><li>Cutting tension cables creates a potential whip </li></ul></ul>10
  140. 140. Precast Concrete (1 of 2) <ul><li>Cast-in-place, monolithic concrete buildings </li></ul><ul><ul><li>Resistant to collapse </li></ul></ul><ul><ul><li>The loss of a column does not necessarily cause collapse. </li></ul></ul><ul><ul><li>Load will be redistributed </li></ul></ul>10
  141. 141. Precast Concrete (2 of 2)‏ <ul><li>Precast concrete buildings </li></ul><ul><ul><li>Individual columns, floors, girders, and wall panels are pinned by connectors </li></ul></ul><ul><ul><li>No protective covering is provided for the connectors </li></ul></ul><ul><ul><li>Fire load must be severe to cause failure </li></ul></ul>10
  142. 142. Explosions in a Precast, Pinned building <ul><li>Such buildings have none of the redundancies of a rigid-framed monolithic concrete building </li></ul><ul><li>Case example: Ronan Point collapse, which involved a 24-story apartment building </li></ul>10
  143. 143. Concrete Trusses <ul><li>Not common </li></ul><ul><li>Exist in the Tampa, Florida, and Dallas/Fort Worth, Texas, airports </li></ul><ul><li>Exist in the American Airlines hanger at Dallas/Fort Worth </li></ul>10
  144. 144. Fires in Concrete Buildings: Case Example 1 <ul><li>Los Angeles Central Library Fire in 1986 </li></ul><ul><li>Loss was immense </li></ul><ul><li>200,000 books and numerous periodical collections were destroyed </li></ul><ul><li>The book stacks provided an estimated 93 pounds per square foot (psf) of fuel </li></ul>10
  145. 145. Fires in Concrete Buildings: Case Example 2 <ul><li>High-rise apartment building in Dallas, Texas </li></ul><ul><li>$340,000 in damage </li></ul><ul><li>Utility and vent pipes had been punched through the ceilings </li></ul>10
  146. 146. Fires in Concrete Buildings: Case Example 3 <ul><li>Military Records Center near St. Louis, Missouri </li></ul><ul><li>Severely damaged in a fire in 1973 </li></ul><ul><li>The incredible fire load included over 21 million military personnel files in cardboard boxes on metal shelves </li></ul>10
  147. 147. Know Your Buildings <ul><li>When building rate is high, difficult for fire departments to keep pace </li></ul><ul><li>Slowdowns present an opportunity to get current on the hazards of specific buildings </li></ul><ul><li>“Experience keeps a dear school, but fools will learn in no other.” </li></ul>10
  148. 148. Summary ( 1 of 2)‏ <ul><li>Concrete is a cementatious material produced by a chemical reaction </li></ul><ul><li>There are two basic types of in-concrete construction: cast-in-place concrete and precast concrete </li></ul><ul><li>Prestressing places engineered stresses in architectural and structural concrete </li></ul>10
  149. 149. Summary ( 2 of 2)‏ <ul><li>Concrete buildings under construction can present serious fire problems </li></ul><ul><li>The concrete in fire-resistive construction serves two purposes—it resists compressive stresses and protects the tensile strength of steel from fire </li></ul>10