Ch 10 Fire-Resistive Construction
Upcoming SlideShare
Loading in...5

Ch 10 Fire-Resistive Construction






Total Views
Views on SlideShare
Embed Views



0 Embeds 0

No embeds



Upload Details

Uploaded via as Microsoft PowerPoint

Usage Rights

© All Rights Reserved

Report content

Flagged as inappropriate Flag as inappropriate
Flag as inappropriate

Select your reason for flagging this presentation as inappropriate.

  • Full Name Full Name Comment goes here.
    Are you sure you want to
    Your message goes here
Post Comment
Edit your comment
  • © Dick Stada/ShutterStock, Inc.
  • Courtesy National Institute of Standards and Technology
  • © Brad Wynnyk/Alamy Images
  • © Marek Pawluczuk/ShutterStock, Inc.
  • © photoslb/ShutterStock, Inc.
  • Photo courtesy of Blaze-tech Fire Protection
  • © EMPICS/Landov
  • © Renyold Ferguson/The St. Louis Post-Dispatch

Ch 10 Fire-Resistive Construction Ch 10 Fire-Resistive Construction Presentation Transcript

  • 10 Fire-Resistive Construction
  • Objectives (1 of 2)‏
    • Recall the difference between noncombustible and fire-resistive construction
    • Describe different types of concrete structural systems
    • Describe the two types of prestressing
  • Objectives (2 of 2)‏
    • Contrast precast and site-cast concrete
    • Describe the hazards of formwork
    • Describe the methods of fireproofing steel and of ensuring a level fire resistance in concrete
    • Detail how compartmentation works to prevent the spread of fire
  • 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
  • Concrete
    • Cementatious material produced by a chemical reaction
    • Cures indefinitely; low temperatures retard the curing of concrete
    • Weak in tensile strength and has poor shear resistance
  • 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
  • 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
  • Today’s Variety of Concrete Structures
    • Use variety of building construction elements
    • Steel-framed buildings now often have cast-in-place concrete floors
    • Precast concrete and prefabricated metal wall panels and decorative brick veneer are common
  • Steel vs. Concrete Framing
    • Designer preferences
      • Some design in steel
      • Others prefer concrete
      • Some buildings concrete-framed and steel-framed mixed together
  • Fire Department Problems
    • Problems with concrete construction
      • Collapse during construction with no fire
      • Fire during construction
      • Fire in completed, occupied buildings
  • Types of Concrete Construction
    • Cast-in-place
      • Plain, reinforced, and post-tensioned concrete
    • Precast
      • Plain, reinforced, and pretension concrete
  • Concrete Definitions (1 of 5)‏
    • Aggregate
    • Cast-in-place concrete
    • Casting
    • Chairs
    • Composite and combination columns
  • Concrete Definitions (2 of 5)‏
    • Composite construction
    • Continuous casting
    • Continuous slipforming
    • Drop panels
    • Flat plate structural system (or continuous beam)‏
  • Concrete Definitions (3 of 5)‏
    • Footings
    • Lally columns
    • Lift slab
    • Monolithic construction
    • Mushroom caps
  • Concrete Definitions (4 of 5)‏
    • One-way structural system
    • Plain concrete
    • Pretensioning and post-tensioning
    • Precast concrete
    • Reinforced concrete
    • Reinforcing bars or rods
  • Concrete Definitions (5 of 5)‏
    • Slipforming
    • Spalling
    • Temperature rods
    • Two-way structural system
  • Concrete Structural Elements
    • Columns
    • Beams (including t-beams) and girders
    • Concrete floors
  • Virtue of Columns
    • High compressive strength and low cost
    • Columns are of reinforced concrete
    • Steel reinforcing rods carry some of the compressive load
    • The compressive strength of steel is many times that of concrete
  • 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
  • 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
  • Beams and Girding (1 of 3) ‏
    • 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
  • Beams and Girding (2 of 3)‏
    • Cantilever beam
      • Tension is in the top of the beam
      • Reinforcing rods are in the top of the beam
  • Beams and Girding (3 of 3)‏
    • 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
  • 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
    • Double T’s are floor slab and beam combinations with two beams
  • Concrete Floors
    • First used for leveling brick and tile arch floors
    • Early floors built of individual beams supporting a floor slab
    • Hollow tiles lightened concrete floors
  • Waffle Concrete
    • Closely spaced beams are set at right angles to one another
    • Unnecessary concrete is formed out
  • Lighter Construction
    • Floor may be just a flat plate
    • This gives a smooth surface
    • Easily finished
  • 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
  • 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
    • Cylindrical openings can be cast lengthwise through the units to remove unnecessary weight
  • 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
  • One-Hour-Rated Designs of Wood Floors
    • Lightweight concrete topping as much as 1 to 1 1/2 inches thick
    • Thickness retards the passage of heat through the floor
    • National Fire Protection Association (NFPA) 251 (American Society of Testing and Materials (ASTM) E119) fire resistance standard
  • 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
  • Concrete Floors in Steel Buildings
    • May be precast or cast-in-place
    • May be only load-bearing or provide structural stability
  • 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
  • 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
  • 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
  • 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
  • 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
  • High-Tensile-Strength Wire
    • Ordinarily used for prestressing
    • More sensitive to high temperatures than structural steel
    • Complete loss of prestress at 800°F
  • Two Methods of Prestressing (1 of 2)‏
    • 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
  • Two Methods of Prestressing (2 of 2)‏
    • Post-tensioning
      • Done on the job site
      • High-tensile-steel strand wires are positioned in the forms
      • After processing, steel tendons are stretched and anchored at the ends of the unit
  • 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
  • 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
  • Ordinary Brick Bearing-Wall Buildings (1 of 2)‏
    • Walls must increase in thickness as the building’s height increases.
    • Limit is generally about 6 stories
    • Recent years, possible to 20 or more stories
  • Ordinary Brick Bearing-Wall Buildings (2 of 2)‏
    • 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
  • Special Cases (1 of 2)‏
    • 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
  • Special Cases (2 of 2) ‏
    • Concrete block
      • Has become popular for some resorts
      • With outside open-air stairways and balconies, life safety is achieved
  • 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
  • Ordering the Removal of a Dangerous Structure
    • Power given to the building commissioner
    • Fire department has no right to demolish such a structure.
  • 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
  • An Industry Warning
    • Experts have warned of the collapse hazard of concrete structures
    • Design engineers should use construction loads as governing loads in structures
  • 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
  • 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 it is surprising is that they are relatively rare
  • 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
  • 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
  • Collapses of Floors (1 of 2)‏
    • Many involve formwork supporting newly cast or high bay floors
    • Proper cross-bracing can help prevent this
  • Collapses of Floors (2 of 2)‏
    • 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
  • 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.”
  • Skyline Towers Collapse
    • Skyline Towers collapsed in Arlington, Virginia, 1973
    • Collapse proved the fallacy
    • Shoring had been removed from the topmost floor
    • The floor collapsed, and the collapse was progressive
  • 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
  • Hazards of Post-Tensioning (1 of 2)‏
    • Hydraulic jacks are used to tension the tendons or jack the cables
    • No bond between the tendons and the concrete
  • Hazards of Post-Tensioning (2 of 2)‏
    • 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
  • Collapse of Reinforced Masonry
    • Used widely in construction
    • Workers might overload a floor portion
    • Case example: In Pittsburgh, Pennsylvania an excess load caused the partial collapse of several stories of precast floors
  • 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: Montgomery County Maryland. Three-story garage collapsed due to oversized washer
  • Lift-slab Collapses (1 of 3)‏
    • 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
  • Lift-Slab Collapses (2 of 3)‏
    • Case example: L’Ambience Plaza concrete building under construction in Connecticut was due to the failure of a single connection
  • Lift-Slab Collapses (3 of 3)‏
    • When do the accidents occur?
      • While the slabs are being lifted or while no lifting is being done
    • 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
  • Fire Problems of Concrete Buildings Under Construction
    • Concrete buildings under construction can present serious fire problems
    • Fire in formwork can easily result in major collapse
    • Little reserve strength in formwork
    • Little understanding of potential hazard
  • Potential Fires at a Construction Site
    • 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
  • Hazard of Heating
    • Burning of scrap wood in steel barrels or the use kerosene heaters are hazards
    • Liquefied petroleum gas (LPG) is also dangerous
  • Codes for LPG (1 of 2)‏
    • 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
  • Codes for LPG (2 of 2)‏
    • Install excess flow valves.
      • Case example: In one city, gas stored and piped with plastic tubes at ground level; hazard should line break
  • Hazards of Post-Tensioned Concrete (1 of 2)‏
    • 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
  • Hazards of Post-Tensioned Concrete (2 of 2)‏
    • 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
  • Protection of Tendons
    • Insist on fireproofing tendon anchors immediately after tensioning is completed
    • Insist on temporary protection for incrementally tensioned tendons
  • 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
  • Precast Buildings (2 of 2)‏
    • Pose unique hazards while being constructed
    • Construction involves erection of precast concrete units.
  • Precast Buildings (2 of 2)‏
      • Temporary bracing or support is used; it can collapse
      • Columns can be braced with wood rather than by telescoping tubular steel braces; wood is flammable
      • Cold-drawn steel cables often provide diagonal bracing in precast buildings; these fail at 800° F
  • Cantilevered Platforms
    • Used by cranes delivering materials to buildings under construction
    • Are braced by wooden shores that would fail in a fire
  • 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
  • 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
  • Falsework: Case Example
    • Formwork for concrete placement burned on the 23 rd to 25 th 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
  • 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
  • Characteristics of Concrete
    • Inherently noncombustible
    • Some people confuse noncombustibility with fire resistance
    • Neither is synonymous with fire safety
  • Safety of Concrete Construction: Case Example
    • Reinforced concrete Joelma building in Sao Paulo, Brazil, burned in 1974
    • Resulted in179 deaths. The structure had minor damage.
  • 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
  • Types of Fireproofing (1 of 2)‏
    • Individual fireproofing provides protection for each piece of steel
    • Methods include encasement and intumescent coating
    • Membrane fireproofing does not protect individual members
  • Types of Fireproofing (2 of 2)‏
    • One method uses a rated floor-ceiling assembly
    • Underwriters Laboratories can test a roof and ceiling assembly
    • NFPA 251 (ASTM E119) standard fire test
  • 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
  • Ceiling System
    • At the mercy of those have reason to remove ceiling tiles
    • Access to utilities and additional storage space are two reasons to remove tiles
  • Legal Provisions
    • None require membrane protection be maintained
    • Replacement acoustical tile may be combustible
    • All penetrations of the ceiling must be rated as part of the ceiling system
  • 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
  • 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
    • Testing doesn’t include superimposed loads
  • 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
  • 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
  • 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
  • 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
  • Deep, Long-span Trusses
    • In some buildings, used to provide clear floor areas
    • This 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
  • 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
  • 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
  • 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
  • Fireproofing and Building Codes
    • Fireproofing
      • Applied to meet the standards required by the local building code
      • Further, building department will indicate which systems tested at which laboratories are acceptable.
  • Efficiency of Fireproofing
    • Depends on the competence of the subcontractor
    • Also depends on the building department staff and on the fire department inspectors
  • 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 three-inch terra cotta tiles, but still burned and failed
  • Errors in Encasement
    • Leaving the bottom web of beams unprotected
    • Skewbacks, which are tiles shaped to fit around steel, corrects this error
    • Skewbacks, however, often are removed for other reasons
  • 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
  • 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
  • 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
  • Disadvantage of Concrete
    • Its weight
    • Fireproofing is often a tempting target for cutting back
    • Case example: Builders replace concrete with wire laths covered with cement plaster or gypsum, both of which are lighter
  • 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
  • Issues with Sprayed-on Material (1 of 2)
    • Importance not understood by other trades
      • Case example: A building with fireproofing stripped from the columns by plasterers
  • Issues with Sprayed-on Material (2 of 2)
      • 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
  • Asbestos Fiber Fireproofing
    • Serious health hazard in its use
    • Difficult to sell a building with asbestos fireproofing
    • Asbestos is being removed from existing buildings
  • Signs of Trouble
    • Deteriorated concrete
    • Spalling that exposes reinforcing rods
    • Cracks in concrete
  • Parking Garages
    • When salt is used to melt snow and ice, corrosion is prevalent
    • Damage is often difficult to determine
  • Calcium Chloride
    • Added to concrete
    • Has caused problems
    • Preventive measures include sealing the concrete, providing adequate drainage, and flushing surfaces with fresh water in the spring
  • Concrete Rehabilitation
    • Includes removal and replacement
    • Installation of cathodic protection
    • Using additional steel beams
  • Unprotected Steel (1 of 4)‏
    • Concrete structures
      • Often repaired with steel
    • Steel cables fail even below 800°F
  • Unprotected Steel (2 of 4)‏
    • 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
  • Unprotected Steel (3 of 4)‏
      • Case example: Fire fighter student saw structural problem with mall roof: owner did not want building department to know of problem
  • Unprotected Steel (4 of 4)‏
    • Steel designed into the structure
      • Proper degree of fireproofing is usually specified
      • If it is not designed into a structure, it is usually unprotected
  • Ceiling Finish and Voids
    • Concrete construction has no inherent voids
    • Finish stages of the building can create voids
  • 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
  • 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
  • Combustible Tile
    • Need not be suspended to create a serious hazard
    • Flammable adhesive create problems
    • Installing new ceilings below old combustible tile ceilings presents a serious hazard
    • Case example: John Sevier Retirement Center fire
  • Combustible Voids
    • Can be created in a variety of ways
    • Case example: A wooden suspended ceiling installed in an otherwise concrete construction. Sprinklers are below the ceiling. Fire could burn unchecked in the void
  • 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
  • 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
  • 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
  • Building Use
    • Requires floor be penetrated
    • Often, such penetrations compromise the integrity of the floor
  • 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
  • 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
  • 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
  • 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
  • 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
  • Concrete’s Behavior in Fires
    • Concrete in fire-resistive construction
      • Resists compressive stresses
      • Protects the tensile strength of steel from fire
      • The concrete provides time to extinguish a fire
  • 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
  • Cutting Tensioned Concrete (1 of 2)‏
    • Fire tactics
      • Can include cutting through a concrete floor for accessibility
      • Hole cutter can cut a hole in conventional reinforced concrete and reinforcing rods
  • Cutting Tensioned Concrete (2 of 2)‏
    • Tensioned concrete structures
      • Steel cables are under tremendous tension
      • Cutting tension cables creates a potential whip
  • Precast Concrete (1 of 2)
    • Cast-in-place, monolithic concrete buildings
      • Resistant to collapse
      • The loss of a column does not necessarily cause collapse.
      • Load will be redistributed
  • Precast Concrete (2 of 2)‏
    • 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
  • Explosions in a Precast, Pinned building
    • Such buildings have none of the redundancies of a rigid-framed monolithic concrete building
    • Case example: Ronan Point collapse, which involved a 24-story apartment building
  • Concrete Trusses
    • Not common
    • Exist in the Tampa, Florida, and Dallas/Fort Worth, Texas, airports
    • Exist in the American Airlines hanger at Dallas/Fort Worth
  • Fires in Concrete 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
  • Fires in Concrete Buildings: Case Example 2
    • High-rise apartment building in Dallas, Texas
    • $340,000 in damage
    • Utility and vent pipes had been punched through the ceilings
  • Fires in Concrete Buildings: Case Example 3
    • Military Records Center near St. Louis, Missouri
    • Severely damaged in a fire in 1973
    • The incredible fire load included over 21 million military personnel files in cardboard boxes on metal shelves
  • 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.”
  • Summary ( 1 of 2)‏
    • 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
  • Summary ( 2 of 2)‏
    • Concrete buildings under construction can present serious fire problems
    • The concrete in fire-resistive construction serves two purposes—it resists compressive stresses and protects the tensile strength of steel from fire