Ch 9 Noncombustible Construction
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Ch 9 Noncombustible Construction






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Ch 9 Noncombustible Construction Ch 9 Noncombustible Construction Presentation Transcript

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