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Ch 9 Noncombustible Construction


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Ch 9 Noncombustible Construction

  1. 1. 9 Noncombustible Construction
  2. 2. Objectives (1 of 2)‏ <ul><li>Understand the difference between noncombustible and fire-resistive construction </li></ul><ul><li>Identify the different types of steel building components and their characteristics </li></ul>9
  3. 3. Objectives (2 of 2)‏ <ul><li>Describe different types of steel structural systems </li></ul><ul><li>Describe the hazards of a metal deck roof fire </li></ul><ul><li>Understand the hazards of high fire loads in unprotected steel structures and ways to improve the situation </li></ul>9
  4. 4. Introduction <ul><li>Noncombustible and fire resistive construction </li></ul><ul><ul><li>Differ in the level of fire resistance assigned to the structural frame, walls, floors, and roof </li></ul></ul><ul><li>Noncombustible construction has little fire resistance </li></ul><ul><li>Fire resistive construction has moderate to heavy fire resistance </li></ul>9
  5. 5. Noncombustible Construction <ul><li>Allowable area and height is much less than fire resistive construction </li></ul><ul><li>Maximum height is 12 stories </li></ul><ul><li>Fire resistive can have unlimited height </li></ul><ul><li>Fire-resistive construction can use steel for its framing system </li></ul>9
  6. 6. Steel <ul><li>Modulus of elasticity about 29 million pounds per square inch (psi)‏ </li></ul><ul><li>High tensile strength and shear strength </li></ul><ul><li>Strong but lightweight members have little inherent fire resistance </li></ul>9
  7. 7. Fire Characteristics of Steel <ul><li>Substantial elongation </li></ul><ul><li>Above 1300°F, steel members may fail </li></ul><ul><li>Cold-drawn steel will fail at about 800°F </li></ul><ul><li>Steel transmits heat readily </li></ul>9
  8. 8. Unwarranted Assumptions <ul><li>False belief in steel’s “fireproofness” </li></ul><ul><li>Need to set priorities </li></ul><ul><ul><li>Heat absorbed by contents or structural elements is the most important heat </li></ul></ul><ul><ul><li>Heat being evolved from contents that are burning is of secondary importance </li></ul></ul><ul><ul><li>Heat leaving the structure—let it go </li></ul></ul>9
  9. 9. Water on Hot Steel <ul><li>Water is the fire department’s heat removal medium </li></ul><ul><li>Myth: Water should not be thrown on heated steel </li></ul><ul><li>Cooling effect of water draws steel back to its original dimensions </li></ul>9
  10. 10. Definitions: Steel Construction Members (1 of 3)‏ <ul><li>Angles </li></ul><ul><li>Bars </li></ul><ul><li>Box columns </li></ul><ul><li>Box girders </li></ul><ul><li>Channels </li></ul>9
  11. 11. Definitions: Steel Construction Members (2 of 3)‏ <ul><li>I-beams </li></ul><ul><li>Plates </li></ul><ul><li>Purlins </li></ul><ul><li>Rolled or built-up members </li></ul><ul><li>Spandrel girders </li></ul>9
  12. 12. Definitions: Steel Construction Members (3 of 3)‏ <ul><li>Tees </li></ul><ul><li>Tubes </li></ul><ul><li>Weight </li></ul><ul><li>Wide-flange shapes </li></ul><ul><li>Zees </li></ul>9
  13. 13. Steel as a Construction Material (1 of 2)‏ <ul><li>Makes it possible to erect tall buildings </li></ul><ul><li>Has consistency in structural characteristics </li></ul><ul><li>Can be connected to other structural elements </li></ul><ul><li>Used for fire escapes </li></ul>9
  14. 14. Steel as a Construction Material (2 of 2)‏ <ul><li>Provides the tensile strength that concrete lacks </li></ul><ul><li>Used in concrete flooring systems </li></ul><ul><li>Used to repair failures in concrete buildings </li></ul>9
  15. 15. Steel Buildings <ul><li>Used in peaked roofs </li></ul><ul><li>Bar joists span the main trusses to support a flat roof </li></ul><ul><li>Steel is almost universally unprotected. </li></ul><ul><li>Buildings often can only be classified as noncombustible </li></ul>9
  16. 16. Protected Noncombustible Sprinklered Construction <ul><li>Found occasionally </li></ul><ul><li>Major structural elements have fire resistance </li></ul><ul><li>Building itself is not fire resistive </li></ul>9
  17. 17. Rigid Frames <ul><li>Column is narrow at the base and tapers to its widest point at the top </li></ul><ul><li>Girder is also tapered </li></ul><ul><li>Wide haunch resists the outward thrust of the roof </li></ul><ul><li>Clear spans of about 100 feet </li></ul>9
  18. 18. Steel-Framed Buildings <ul><li>Many are prefabricated </li></ul><ul><li>Butler Company is a prominent manufacturer </li></ul>9
  19. 19. Huge Spans <ul><li>Span collapses can be sudden and tragic </li></ul><ul><ul><li>Adjacent bents are tied together </li></ul></ul><ul><ul><li>Tying the steel units together creates dependencies between torsional or eccentric loads </li></ul></ul><ul><ul><li>The higher the resistance to wind load, the more likely a progressive collapse </li></ul></ul>9
  20. 20. Developing Wide-Span Trusses <ul><li>Designs may push the limits of steel </li></ul><ul><li>Hasty field changes or errors in construction can have catastrophic consequences </li></ul>9
  21. 21. Deep Parallel-Chord Trusses <ul><li>Floor beams in hospitals </li></ul><ul><li>Interstitial space </li></ul><ul><ul><li>Such voids should not be used for storage or maintenance </li></ul></ul><ul><ul><li>Automatic sprinklers should be required </li></ul></ul>9
  22. 22. Heavy Parallel-Chord Trusses <ul><li>Have been used as transfer beams </li></ul><ul><li>Often hidden in partition walls </li></ul>9
  23. 23. Trussed Arches <ul><li>Arch of a steel arch bridge is often a truss </li></ul><ul><li>Is a compression structure </li></ul>9
  24. 24. Walls of Steel-Framed Buildings <ul><li>Wall composition varies </li></ul><ul><li>Metals, cement-asbestos board, masonry, concrete, and reinforced plastics found </li></ul><ul><li>Wall insulation and coatings also factors </li></ul>9
  25. 25. Cement-Asbestos Board <ul><li>Noncombustible and is often used for friable construction </li></ul><ul><li>Friable construction is used where an explosion is a possibility </li></ul><ul><li>Will break away readily and relieve pressure </li></ul>9
  26. 26. Glass-Fiber Reinforced Plastics <ul><li>Noncombustible </li></ul><ul><li>Resinous binder most often used with it is flammable </li></ul>9
  27. 27. Aluminum <ul><li>Noncombustible, but has a low melting point </li></ul><ul><li>Has little mass per unit of area, so it disintegrates rapidly in a fire </li></ul>9
  28. 28. Precast Prestressed Concrete Panels <ul><li>Usually erected in large sections </li></ul><ul><li>Collapse is hazardous to fire fighters </li></ul>9
  29. 29. Masonry Walls <ul><li>Often used for walls for unprotected steel-framed buildings </li></ul><ul><li>Made of concrete block or a composite </li></ul><ul><li>Usually only curtain walls </li></ul><ul><li>Important to analyze the effect of the expansion of the steel frame on the wall </li></ul>9
  30. 30. Galvanized Steel Walls <ul><li>Used when heat conservation is not important </li></ul><ul><li>Asphalt asbestos protected metal (AAPM)‏ </li></ul><ul><li>Robertson Protected Metal (RPM) is one proprietary name </li></ul>9
  31. 31. Metal Panels <ul><li>Prefabricated metal panels in a sandwich construction </li></ul><ul><li>Plastics are often used with metal panels </li></ul><ul><li>Insulation, vapor seal, or adhesive in the panels may be combustible </li></ul>9
  32. 32. Polyurethane Insulating Panels <ul><li>Protected by gypsum board and stainless-steel sheathing </li></ul><ul><li>If a cutting torch is later used, a smoky, destructive fire may result </li></ul>9
  33. 33. Aluminum Sandwich Panels <ul><li>Can be made with foamed polyurethane </li></ul><ul><li>Some are listed by Underwriters Laboratories (UL) Inc. for low flame spread ratings </li></ul><ul><li>Smoke-developed ratings may be quite high </li></ul>9
  34. 34. Failure of the Closure of the Wall Panel to the Floor Slab <ul><li>Design of panel walls </li></ul><ul><li>Method of installation </li></ul><ul><li>Degradation of insulation </li></ul><ul><li>Expansion of metal under fire conditions </li></ul>9
  35. 35. High-Rise Framing <ul><li>Steel once stood unchallenged as a method for high-rise buildings </li></ul><ul><li>Concrete now is finding more use </li></ul>9
  36. 36. Builders’ Hesitation <ul><li>Brick, stone, and terra cotta added to framed buildings </li></ul><ul><li>Goal was to reduce the apparent or perceived height of the building </li></ul><ul><li>Didn’t openly discuss use of steel-frames </li></ul>9
  37. 37. Tilt-Slab Hazards <ul><li>Walls braced with tormentors or braces until the roof secured </li></ul><ul><li>If the roof is being lost in the fire, beware of wall collapse </li></ul><ul><li>If heavy smoke is present, the sprinklers are not controlling the fire </li></ul>9
  38. 38. Steel-Framed Buildings Under Construction <ul><li>Wind forces must be resisted, because the building is not fully connected </li></ul><ul><li>Braces may not be properly installed </li></ul>9
  39. 39. Plastic Design in Steel Construction <ul><li>Connections are built to transfer loads beyond the column </li></ul><ul><li>Beams are lighter and columns are smaller than they would be otherwise </li></ul><ul><li>The lighter the steel, the less fire resistance </li></ul>9
  40. 40. More on the Fire Characteristics of Steel <ul><li>Conducts heat </li></ul><ul><li>Elongates as temperature increases </li></ul><ul><li>Loses strength at high temperatures </li></ul>9
  41. 41. Steel Conducts Heat <ul><li>Steel transmits heat </li></ul><ul><li>Tin ceilings can transmit fire </li></ul><ul><li>The conductivity of steel can be a factor in spreading fires </li></ul>9
  42. 42. Ships <ul><li>Practice of using ships as buildings is growing </li></ul><ul><li>Ships have steel walls known as bulkheads </li></ul><ul><li>Welding operations are performed without concern for heat transmission </li></ul>9
  43. 43. Self-Storage Facilities <ul><li>Have many of the characteristics of ships </li></ul><ul><li>Fire can spread from unit to unit by conduction and radiation </li></ul>9
  44. 44. Steel Elongates <ul><li>Expands from 0.06 percent to 0.07 percent for each 100°F rise </li></ul><ul><li>At 1000°F, a steel member will expand 9 1/2 inches over 100 feet of length </li></ul><ul><li>Above 1000°F, steel starts to soften and fail </li></ul>9
  45. 45. Elongating Steel <ul><li>Exerts a lateral force against the structure that restrains it </li></ul><ul><li>Expansion of steel may cause the displacement of masonry </li></ul>9
  46. 46. Hot, Fast Fires Effect on Steel Buildings <ul><li>Failure temperatures are reached rapidly </li></ul><ul><li>Lateral thrust against the wall is minimized </li></ul><ul><li>Overturning can be anticipated </li></ul>9
  47. 47. Steel Fails <ul><li>Steel above 1000°F starts to lose strength rapidly </li></ul><ul><li>National Fire Protection Association (NFPA) 251 (American Society of Testing and Materials (ASTM) E119) test reaches 1000°F in five minutes </li></ul><ul><li>National Institute of Standards and Technology (NIST) test reaches 1500°F in five minutes </li></ul>9
  48. 48. Standard Tests of the Fireproofing of Steel Columns <ul><li>Test ends when a temperature of 1200°F is exceeded at one point or 1000°F is exceeded on the average in the column </li></ul><ul><li>A principle variable is the weight or mass of the steel unit </li></ul><ul><li>Ventilation is also a factor </li></ul>9
  49. 49. Overcoming the Negative Fire (1 of 2) ‏ <ul><li>Ignore the problem </li></ul><ul><li>Rely on an inadequate code </li></ul><ul><li>Take a calculated risk </li></ul><ul><li>Fireproof (insulate) the steel </li></ul>9
  50. 50. Overcoming the Negative Fire (2 of 2)‏ <ul><li>Protect the steel with sprinklers </li></ul><ul><li>Fireproof the steel with a water cooling system </li></ul><ul><li>Locate the steel out of range of the fire </li></ul>9
  51. 51. Ignoring the Problem <ul><li>Potential for fire damage to steel buildings is not clearly understood </li></ul><ul><li>Unwarranted confidence on the fact that the steel is noncombustible </li></ul>9
  52. 52. Steel Highway Structures and Bridges <ul><li>Unprotected steel that is vulnerable to an occasional gasoline truck fire </li></ul><ul><li>New York City Fire Department has had preplans in place for the East River bridges for over 70 years </li></ul>9
  53. 53. Hazards of Concentrated Fire Loads (1 of 2)‏ <ul><li>Unprotected steel buildings may have highly concentrated fire loads </li></ul><ul><li>“One-high story” buildings with internal structures </li></ul><ul><ul><li>Mezzanines, sometimes built of wood </li></ul></ul><ul><ul><li>Other combustible spaces </li></ul></ul>9
  54. 54. Hazards of Concentrated Fire Loads (2 of 2)‏ <ul><li>Metal trailers are hazardous, especially when grouped </li></ul><ul><li>Prefabricated buildings, especially with certain types of insulation in walls </li></ul>9
  55. 55. Excavation Bracing <ul><li>Building excavations are being made much deeper </li></ul><ul><li>Walers and rakers </li></ul><ul><li>An excavation is loaded with combustibles </li></ul><ul><li>Tiebacks  </li></ul>9
  56. 56. Buildings Under Construction <ul><li>Steel may be unprotected for extended periods </li></ul><ul><li>World Trade Center used ordinary plywood to save $1 million </li></ul>9
  57. 57. Relying on Inadequate Codes <ul><li>Building Codes </li></ul><ul><ul><li>Unprotected noncombustible or protected noncombustible </li></ul></ul><ul><ul><li>“Protection” refers to physical protection of the steel with gypsum board, spray-on fireproofing, or the like </li></ul></ul>9
  58. 58. Study the Type of Construction <ul><li>Column, girder, and beam construction is common </li></ul><ul><li>If a masonry bearing wall is substituted for some of the exterior columns, the building is wall-bearing </li></ul>9
  59. 59. Assumption About Fires <ul><li>They burn only upwards </li></ul><ul><li>Example: A fire involving a wooden balcony or a metal deck roof could well cause steel framing to move and thus cause brick-veneered walls to fall </li></ul>9
  60. 60. Steel High Above the Floor <ul><li>Codes vary in terms of protection of steel buildings </li></ul><ul><li>Heights 20-30 feet above the floor are often left unprotected as risks are thought to be low </li></ul>9
  61. 61. The McCormick Place Fire <ul><li>The main exhibit area provided a clear area of 320,000 square feet </li></ul><ul><li>The columns were trusses themselves. </li></ul><ul><li>The columns were fire protected up to a height of 20 feet </li></ul><ul><li>The roof trusses were unprotected </li></ul>9
  62. 62. What Could Have Been Done Better <ul><li>Modern building codes would have required automatic sprinkler system </li></ul><ul><li>Sprinklers could have limited the spread of this fire </li></ul><ul><li>Codes were inadequate </li></ul>9
  63. 63. The New McCormick Place <ul><li>Structural steel is protected with directly applied fireproofing delivering one-hour fire resistance </li></ul><ul><li>The entire building is sprinklered </li></ul><ul><li>Provisions have been made for smoke venting </li></ul>9
  64. 64. Important Test Experiences <ul><li>Underwriters Laboratories tested in the aftermath of the fire </li></ul><ul><li>Tests done in building 30 feet high with typical fuels </li></ul><ul><li>The first test fires had 1500°F after 5 minutes and 45 seconds </li></ul><ul><li>A bar joist reached 1540°F and an I-beam 1355°F in just over 5 minutes </li></ul>9
  65. 65. Taking Calculated Risks <ul><li>Financial Calculation </li></ul><ul><li>Engineering Calculation </li></ul><ul><li>“Forgetting It” Calculation </li></ul><ul><li>Steel Industry </li></ul>9
  66. 66. Insulated Metal Deck Roof Fire Problems <ul><li>Fire in the General Motors transmission plant at Livonia, Michigan </li></ul><ul><li>The metal deck roof was the principal contributing factor to the destruction of the plant. </li></ul>9
  67. 67. Insulation <ul><li>Is useless when it absorbs moisture </li></ul><ul><li>Must be protected from capillary attraction </li></ul><ul><li>A bituminous coating serves as the adhesive and sometimes as a moisture-stopping vapor barrier </li></ul>9
  68. 68. An Approved Roof <ul><li>Is one that meets UL standards </li></ul><ul><li>Can be UL listed but still be a combustible metal deck roof </li></ul>9
  69. 69. When a Fire Occurs <ul><li>The metal deck heats up </li></ul><ul><li>Heat is conducted through the deck to the bituminous adhesive </li></ul><ul><li>Adhesive liquefies and then vaporizes. </li></ul><ul><li>When the gas mixes with the air below, it ignites from the fire below </li></ul>9
  70. 70. Prevention of Metal Deck Roof Fires <ul><li>Use Factory Mutual Class I roofing or a UL Classified Roof </li></ul><ul><li>Provide adequate automatic sprinkler protection for the roof, even though the contents may be noncombustible </li></ul>9
  71. 71. Fires of Interest (1 of 2)‏ <ul><li>Tinker Air Force Base </li></ul><ul><ul><li>A fire was started by roofers </li></ul></ul><ul><ul><li>The sprinklers were below a wire lath and plaster ceiling </li></ul></ul><ul><ul><li>The water did not hit the underside of the roof deck, and the fire burned unimpeded </li></ul></ul>9
  72. 72. Fires of Interest (2 of 2)‏ <ul><li>Wabush Mines </li></ul><ul><ul><li>A fire in a large building damaged a metal deck roof 90 feet above the floor </li></ul></ul><ul><ul><li>Even if the roof had been Class I, damage would have been severe </li></ul></ul>9
  73. 73. Class I <ul><li>Some think it means “completely satisfactory under all circumstances” </li></ul><ul><li>A Class I roof with any combustibles should not be used over a high-value installation </li></ul>9
  74. 74. Atomic Energy Commission (AEC)‏ <ul><li>Studied fire protection for thousands of acres of metal deck roofs </li></ul><ul><li>Decided to add sprinklers to government plants </li></ul><ul><li>Over $20 million was spent on sprinklers and water supplies </li></ul>9
  75. 75. An Unrecognized Problem (1 of 2)‏ <ul><li>Metal deck roof a factor in many losses </li></ul><ul><li>Common characteristics of metal-deck roof fires </li></ul><ul><ul><li>Small openings allow rapid fire spread </li></ul></ul><ul><ul><li>Thick, black, choking smoke, sometimes with dripping tar </li></ul></ul>9
  76. 76. An Unrecognized Problem (2 of 2)‏ <ul><li>Fire suppression group may not understand the significance of these fires; building codes often are inadequate </li></ul>9
  77. 77. Fighting the Metal Deck Roof Fire <ul><li>Marine Corps Supply Depot in Norfolk, Virginia </li></ul><ul><li>Marine plywood office </li></ul>9
  78. 78. Metal Decks on Nonmetal Buildings <ul><li>Metal decks found on steel-framed buildings as well as masonry buildings </li></ul><ul><li>Kensington, MD Fire </li></ul><ul><ul><li>In December 1970, a fire broke out in a janitor supply business </li></ul></ul><ul><ul><li>Chief identified as probable metal-deck roof fire </li></ul></ul>9
  79. 79. Types of Protection of Steel Structures <ul><li>Unprotected </li></ul><ul><li>Dynamic protection </li></ul><ul><li>Passive protection </li></ul><ul><li>Passive/dynamic combination </li></ul>9
  80. 80. Unprotected Steel <ul><li>Has potential for early collapse </li></ul><ul><li>Wichita, Kansas automobile showroom fire </li></ul><ul><li>Repair bays built of lightweight steel truss construction </li></ul>9
  81. 81. Need to Cool All Heated Steel <ul><li>The quantity of water is not excessive </li></ul><ul><li>Cool all the steel that is within reach of hose streams and give special attention to columns </li></ul><ul><li>Solid stream tip might be better than a fog tip </li></ul>9
  82. 82. Water Damage <ul><li>Some argue against the use of water because of the damage it can cause </li></ul><ul><li>If owners had sprinklered the building, water would be discharged anyway </li></ul>9
  83. 83. Dynamic Fire Protection <ul><li>Accomplished with various types of automatic sprinkler systems </li></ul><ul><li>Hydraulically calculated sprinkler design is no guarantee of success </li></ul><ul><li>Heavy structural steel sometimes is protected by special lines of sprinklers. </li></ul><ul><li>Deluge and fog/foam systems used for flammable liquids </li></ul>9
  84. 84. Passive Fire Protection (1 of 2)‏ <ul><li>Is the legally required level of fire resistance adequate for the fire load as it exists in the building? </li></ul><ul><li>Has the protection of steel been provided, and is it maintained? </li></ul><ul><li>Is there any legal relief? </li></ul>9
  85. 85. Passive Fire Protection (2 of 2)‏ <ul><li>Is it up to the fire department simply to do the best it can in the event of a fire? </li></ul><ul><li>If the fire department estimate of the situation indicates potential or inevitable disaster, who, if anyone, is notified? </li></ul>9
  86. 86. What All Personnel Should Know <ul><li>The requirements for fire resistance as applied to specific buildings </li></ul><ul><li>The manner in which fire protection can be degraded is also crucial </li></ul>9
  87. 87. Degradable Methods <ul><li>Sprayed-on protection </li></ul><ul><li>Membrane fireproofing </li></ul><ul><li>Fire-rated tile </li></ul><ul><li>Considerations </li></ul><ul><ul><li>Permitted under local code? </li></ul></ul><ul><ul><li>Could tampering have occurred which might make less effective? </li></ul></ul>9
  88. 88. Passive/Dynamic Protection <ul><li>Partial static protection (such as a spray-on coating) used along with automatic sprinklers </li></ul>9
  89. 89. Code Problems <ul><li>Develop competence </li></ul><ul><ul><li>One person or group should become familiar with current and past local building codes </li></ul></ul><ul><li>Building officials may be less than enthusiastic about fire fighter involvement. </li></ul><ul><li>Some fire prevention managers are equally unenthusiastic about fire fighter involvement </li></ul>9
  90. 90. Code Variances <ul><li>Code exceptions might be made by building and fire prevention officials </li></ul><ul><li>Codes do not permit waivers to specific requirements </li></ul><ul><li>All modifications to requirements of the code should be fully documented </li></ul>9
  91. 91. Preplanning Your “McCormick Place” <ul><li>Make your own case study </li></ul><ul><ul><li>Consider a possible preplan of a fire in an unprotected steel building being used as an exhibit hall </li></ul></ul><ul><ul><li>Assume there is a balcony running down both sides that is used for sports events but not for exhibits </li></ul></ul>9
  92. 92. First Moves in a Case Study <ul><li>Battle for sprinkler protection or denial of the facility to high fire-load exhibits </li></ul><ul><li>After you lose, get in writing an agreement that the fire department can take whatever steps necessary to protect life and property during exhibits </li></ul>9
  93. 93. Consider a Worst Case Scenario (1 of 2)‏ <ul><li>An exhibition with a potential for a high rate of heat release in a fire </li></ul><ul><li>A hot, fast fire is anticipated indicates a more severe test of the structure than a slower fire </li></ul>9
  94. 94. Consider a Worst Case Scenario (2 of 2)‏ <ul><li>Do you need an alternative automatic system? </li></ul><ul><li>Study the potential water supply and needs </li></ul>9
  95. 95. Be Proactive <ul><li>Watch for new ideas </li></ul><ul><li>Step-by-step logic leads to the practical solution </li></ul>9
  96. 96. Summary (1 of 2)‏ <ul><li>Steel is the most important metal used in building construction </li></ul><ul><li>Steel has several important characteristics to consider regarding its behavior in fire. </li></ul>9
  97. 97. Summary (2 of 2) ‏ <ul><li>Steel structures can be divided into the following types: </li></ul><ul><ul><li>Unprotected </li></ul></ul><ul><ul><li>Dynamically protected </li></ul></ul><ul><ul><li>Passively protected </li></ul></ul><ul><ul><li>Passive/dynamic combination protection </li></ul></ul>9