6 Building Construction. 2 Objectives Describe the characteristics of building materials: masonry,...

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Building Construction

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Objectives• Describe the characteristics of building materials: masonry,

concrete, steel, glass, gypsum board, and wood.• List the characteristics of each type of building construction:

fire-resistive construction, noncombustible construction, ordinary construction, heavy timber construction, and wood-frame construction.

• Describe how each of the five types of building construction react to fire.

• Describe the function of each of the following building components: foundations, floors, ceilings, roofs, trusses, walls, doors, windows, interior finishes, and floor coverings.

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Introduction• Knowing building construction enables fire fighters

to:– Predict how a fire will spread– Make determinations about structural integrity– Recognize warning signs of imminent collapse

• Fire risks also depend on occupancy and contents.

• Occupancy: how a building is used• Contents: vary, but usually related to building use

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Construction Material Properties and Fire Behavior

• Key factors affecting combustibility:– Combustibility– Thermal conductivity– Loss of strength when heated– Rate of thermal expansion

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Types of Construction Materials

• Masonry• Concrete• Steel and other metals• Glass• Gypsum board• Wood• Plastics

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Masonry

• Inherently fire-resistive

• Poor conductor of heat

• Openings can allow fire to spread.

• With prolonged exposure to fire, masonry can collapse.

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Concrete

• Inherently fire-resistive

• Poor conductor of heat

• Strong under compression

• Weak under tension

• Can be damaged through exposure to fire

– Spalling

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Steel• Strongest material in common use• Strong in both compression and

tension• Will rust if exposed to air and

moisture• Not fire-resistive• Good conductor of heat• Expands and loses strength when

heated• Any sign of bending, sagging, or

stretching indicates immediate risk of failure.

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Other Metals

• Aluminum– Often melts and drips in fires

• Copper– Primarily used for piping and wiring

• Zinc– Primarily used as a protective coating for

metals

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Glass

• Noncombustible, but not fire-resistive

• Ordinary (non-treated) glass will break when exposed to flame.

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Gypsum Board• Not a strong structural material• Used mainly for finishing • Very good insulator• Limited combustibility

– Paper will burn, but gypsum itself will not.– Often used as a firestop

• Prolonged exposure to fire will cause failure.– Moisture in the material will evaporate causing

deterioration.

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Wood

• Most common building material

• Highly combustible

• Weakens when heated

• Fire-retardant chemicals can weaken wood.

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Plastics

• Rarely used for structural support

• Combustibility varies

• Many plastics release dense, toxic smoke when they burn.

• Thermoplastic materials melt and drip.

• Thermoset materials lose strength but will not melt.

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Construction Type Determination

• Classification based on combustibility and fire resistance

• Codes specify construction type required based on:

– Height– Area– Occupancy– Location

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Types of Construction

• Type I: Fire-Resistive

• Type II: Noncombustible

• Type III: Ordinary

• Type IV: Heavy Timber

• Type V: Wood Frame

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Type I: Fire-Resistive

• All structural components must be noncombustible.

• Used for:– Large numbers of people

– Tall or large area

– Special occupancies

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• Building materials should not provide fuel for a fire.– Contents may burn but the building should not.

• Steel framing must be protected.• Fires can be very hot and hard to ventilate.• In extreme conditions Type I buildings can collapse.

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Type II: Noncombustible

• All structural components must be noncombustible.

• Fire-resistive requirements are less stringent than Type I.

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• Structural components contribute little or no fuel.

• Fire severity is determined by contents.

• Most common in single-story warehouses or factories

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Type III: Ordinary• Used in a wide range of buildings• Masonry exterior walls support

floors and roof.• Usually limited to no more than

four stories• Limited fire resistance

requirements

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• Two separate fire loads:– Construction materials

– Contents

• Fire resistance depends on building age and local building codes.

• Exterior walls, floors, and roof are connected.

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Type IV: Heavy Timber• Exterior masonry walls• Interior structural elements,

floors, and roof of wood• No concealed spaces or voids• Used for buildings as tall as

eight stories• Open spaces suitable for

manufacturing and storage• New Type IV construction is

rare.

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Type V: Wood Frame (1 of 2)

• Most common type of construction in use

• All major components are wood or other combustible materials.– Can rapidly become fully involved– Collapse frequently

• Used in buildings of up to four stories• Wooden I-beams and trusses

– Just strong enough to carry required load– No built-in safety margin– Collapse early and suddenly

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Type V: Wood Frame (2 of 2)

• Balloon-frame construction– Exterior walls assembled

with continuous wood studs from the basement to the roof.

• Platform-frame construction– Exterior wall studs not

continuous.

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Building Components

• Foundation

• Floors and ceilings

• Roofs

• Trusses

• Walls

• Doors and windows

• Interior finishes and floor coverings

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Foundation

• Ensures building is firmly planted

• Helps keep all other components connected

• Weak or shifting foundations can cause collapse.

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Floors and Ceilings

• Fire-Resistive Floors– Floor-ceiling system designed to prevent vertical fire spread– If space above ceiling is not partitioned or sprinklered, fire

can quickly extend horizontally across a large area.

• Wood-Supported Floors– Heavy-timber floors can often contain a fire for an hour or

more.– Conventional wood flooring burns readily and can fail in as

little as 20 minutes.– Modern, lightweight wood I-beams and trusses

• Little fire resistance

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Roofs

• Not designed to be as strong as floors

• Three primary designs:– Pitched roofs– Curved roofs– Flat roofs

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Pitched Roofs

• Sloped or inclined• Can be gable, hip,

mansard, gambrel, or lean-to

• Usually supported by rafters or trusses

• Require some sort of roof covering

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Curved Roofs

• Used for large buildings that require large, open interiors

– Supermarkets– Warehouses– Industrial buildings

• Usually supported by bowstring trusses or arches

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Flat Roofs (1 of 2)

• Usually found on houses, apartment buildings, warehouses, factories, schools, and hospitals

• Have a slight slope for drainage

• Wood support structures use solid wood beams and joists.

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Flat Roofs (2 of 2)

• Lightweight construction techniques employ wood I-beams and trusses.

• Open-web steel trusses (bar joists) often used for support

• Most coverings highly combustible

• Ventilation may involve cutting through many layers of roofing.

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Trusses

• Triangular geometry creates a strong, rigid structure.

• Usually prefabricated wood or steel• Three types:

– Parallel chord• Used for flat roofs and floors

– Pitched chord• Used for pitched roofs

– Bowstring• Used for curved roofs

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Walls

• Most visible part of a building

• Constructed of a variety of materials

• Walls are:– Load-bearing– Nonbearing– Specialized

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Load-Bearing Walls

• Give structural support

• Either interior or exterior

• Support both “dead load” and “live load”

• Damaged wall can result in collapse

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Nonbearing Walls

• Support only their own weight

• Can be breached or removed without compromising structural integrity

• Either interior or exterior

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Specialized Walls (1 of 2)

• Party walls– Common to two properties– Almost always load-bearing– Often a fire wall

• Fire walls– Designed to limit horizontal fire spread– Extend from foundation through roof– Constructed of fire-resistant materials

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Specialized Walls (2 of 2)

• Fire partitions– Interior walls that extend from a floor to underside

of floor above

• Fire enclosures– Fire-rated assemblies that enclose vertical

openings

• Curtain walls– Nonbearing exterior walls attached to the outside

of a building

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Walls

• Solid, load-bearing masonry walls can reach six stories high.

• Nonbearing masonry walls can reach almost any height.

• Never assume that exterior walls are masonry.

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Doors

• Can be used for entry, exit, light, and ventilation

• Mostly constructed of wood or metal– Hollow-core wood doors offer little fire

resistance.– Solid-core doors provide some fire

resistance.– Metal doors more durable and fire-

resistant.

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Window Assemblies

• Used for light, ventilation, entry, and exit

• Window type depends on a variety of factors.

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Fire Doors and Fire Windows• Constructed to prevent

spread of flames, heat, and smoke

• Must meet NFPA 80• Labeled according to

approved-use– Class A– Class B– Class C– Class D– Class E

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• Fire windows are used when a window is needed in a required fire-resistant wall.

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Interior Finishesand Floor Coverings

• Finishes and coverings are exposed interior surfaces of a building.

• Different interior finish materials contribute in various ways to a building fire.

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Construction or Demolition

• Construction or demolition sites pose special problems for fire fighters.

• Built-in fire protection features are often missing.

• Fire-resistive enclosures can be missing.

• Often unoccupied for long periods

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Summary

• Many materials are used in building construction, and each material reacts differently to heat and fire.

• The five types of building construction each have their own strengths and weaknesses and differing levels of resistance to fire.

• Buildings contain a variety of parts or components.

• Materials used in building components vary.

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