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Building Construction

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Chapter 13 Building Construction Introduction Fire departments pride themselves in ability to launch aggressive interior structural attacks Often, buildings collapse ... – PowerPoint PPT presentation

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Title: Building Construction


1
Chapter 13
  • Building Construction

2
Introduction
  • Fire departments pride themselves in ability to
    launch aggressive interior structural attacks
  • Often, buildings collapse without a visual
    warning
  • Firefighters must understand how fire travels
  • Departments need more training on building
    construction

3
Building ConstructionTerms and Mechanics
  • Firefighters need understanding of concepts
    associated with construction
  • Intended use of building can add tremendous
    weight
  • Elements create building loading
  • Imposition of loads causes stress called force
  • Forces delivered to earth for building to be
    structurally sound

4
Types of Loads
  • Two broad categories
  • Dead loads
  • Live loads
  • Specific terms for dead loads and live loads
  • Concentrated load
  • Distributed load
  • Design load
  • Undesigned load
  • Fire load

5
Figure 13-2 The steel stairs and
air-conditioning unit apply a concentrated load
on this roof structure. Also note the potential
instability of the air-conditioning unit placed
on cement blocks.
6
Imposition of Loads
  • Loads must be transmitted to structural elements
  • Terms associated with imposition
  • Axial load
  • Eccentric load
  • Torsion load

7
Figure 13-5 There are three types of loads that
can be transmitted through a structural member
axial, eccentric, and torsion.
8
Forces
  • Loads imposed on materials create stress
  • Stress and strain defined as forces applied to
    materials
  • Compression
  • Tension
  • Shear
  • Several variables determine amount of time a
    material can resist gravity and fire degradation

9
Figure 13-6 Loads are applied to a structural
member as compression, tension, and shear forces.
10
Forces (contd.)
  • Several variables determine amount of time a
    material can resist gravity and fire degradation
  • Material type and mass
  • Surface-to-mass ratio
  • Overall load being imposed
  • BTU development
  • Type of construction (assembly method)

11
Forces (contd.)
  • More variables
  • Alterations (undersigned loading)
  • Age deterioration/care and maintenance of the
    structure
  • Firefighting impact loads
  • Condition of fire-resistive barriers

12
Structural Elements
  • Buildings are an assembly of structural elements
    designed to transfer loads to the earth
  • Can be defined simply as
  • Beams
  • Columns
  • Walls
  • Connections

13
Beams
  • Transfers loads perpendicular to its length
  • Types of beams
  • Simple beam
  • Continuous beam
  • Cantilever beam
  • Lintel
  • Girder
  • Joist
  • Truss and Purlin

14
Figure 13-7 A beam transfers a load
perpendicular to the loadcreating compressive
and tensile forces within the beam.
15
Columns
  • Any structural component that transmits a
    compressive force parallel through its center
  • Typically support beams and other columns
  • Generally vertical supports of building
  • Can be vertical, horizontal, or diagonal

16
Walls
  • Really long, but slender, column
  • Two categories
  • Load-bearing walls
  • Carries weight of beams, other walls, floors,
    roofs, other structural elements
  • Also carries weight of the wall itself
  • Non-load-bearing walls
  • Need only support its own weight
  • Example partition wall between two stores in a
    strip mall

17
Connections
  • Weak link as it relates to structural failure
    during fires
  • Often small, low-mass material that lacks
    capacity to absorb heat
  • Three categories
  • Pinned
  • Rigid
  • Gravity

18
Fire Effects on CommonBuilding Construction
Materials
  • Many factors determine which material is used to
    form structural elements
  • Cost
  • Application
  • Engineering capabilities
  • Adaptability
  • Each material reacts to fire in a different way

19
Table 13-1 Performance of Common Building
Materials under Stress and Fire
20
Wood
  • Most common building material
  • Relatively inexpensive
  • Marginal resistance to forces compared to weight
  • Native wood with more mass takes longer to burn
    before strength is lost
  • Engineered wood
  • Plywood delaminates when exposed to fire
  • Some composites fail through exposure to heat
    without burning

21
Steel
  • Mixture of carbon and iron ore
  • Excellent tensile, shear, and compressive
    strength
  • Popular choice for
  • Girders
  • Lintels
  • Cantilevered beams
  • Columns
  • Loses strength as temperatures increase

22
Concrete
  • Mixture of portland cement, sand, gravel, and
    water
  • Excellent compressive strength
  • All concrete contains some moisture
  • Under heat, moisture expands and causes concrete
    to crack and spall
  • Concrete can stay hot long after the fire is out

23
Masonry
  • Common term that refers to brick, concrete block,
    and stone
  • Used to form load-bearing walls
  • Veneer wall supports its own weight
  • Mortar holds units together and have little or no
    tensile or shear strength
  • Excellent fire-resistive qualities

24
Composites
  • Combination of the four basic materials
  • Includes plastics, glues, and assembly techniques
  • Example wooden I beams composed of wood chips
    and veneers pressed together in I-shape
  • Structurally stronger but fail quickly when
    heated
  • No fire contact required
  • Steel expands faster than wood, causing stress at
    intersection between the two materials

25
Figure 13-11 A composite truss. Rapid heating
will cause the stamped-steel to separate from the
wood chords.
26
Types of Building Construction
  • Five broad categories of building construction
    have been developed
  • Give firefighters basic understanding of
  • Arrangement of structural elements
  • Materials used to construct building
  • Broad classifications are dangerously incomplete
    for firefighters
  • Buildings are built to meet certain codes

27
Type I Fire Resistive
  • Elements are of an approved
  • non-combustible or limited combustible material
  • Typical of Type I
  • Monolithic-poured cement
  • Steel with spray-on fire protection coatings
  • Typically large multi-storied structures with
    multiple exit points
  • Examples arenas, high-rises, World Trade Center

28
Figure 13-15 A typical Type I building, with
structural members designed to resist the effects
of fire for three to four hours. This building is
of reinforced concrete construction.
29
Type II Non-combustible
  • Not qualified for Type I construction
  • Are of an approved non-combustible or limited
    combustible material
  • Type II buildings are steel
  • Warehouses
  • Small arenas
  • Newer churches
  • Steel not required to have fire-resistant coating
  • Susceptible to deformation

30
Figure 13-16 Buildings of Type II construction
will have structural elements with little or no
protection from the effects of fire. Remember, in
the event of a fire, these unprotected steel
structural members may fail and collapse quickly.
31
Type III Ordinary
  • Buildings where load-bearing walls are
    non-combustible
  • Roof and floor assemblies are wood
  • Prevalent in most older town main street areas
  • Many void spaces where fire can spread undetected
  • Common hallways, utilities, attics
  • Masonry walls hold heat inside, floors and roof
    beams gravity fit

32
Figure 13-17 Buildings of Type III, ordinary
construction, are common throughout North
America. These typical Downtown USA buildings
provide many challenges to firefighters, such as
void spaces and common walls allowing rapid fire
extension and little structural protection.
33
Type IV Heavy Timber
  • Block or brick exterior load-bearing walls and
    interior structural members, roofs, floors, and
    arches of solid or laminated wood without
    concealed spaces
  • Buildings are quite stout
  • Used for warehouses, manufacturing buildings,
    older churches
  • New Type IV buildings hard to find
  • Cost of large-dimension lumber and laminated wood
    beams makes this building type rare

34
Figure 13-19 Type IV buildings, heavy timber
construction, have large wood structural elements
with great mass. The mass of these structural
members requires a long burn time for failure.
The connections, usually steel, are the weak
points in this type of construction.
35
Figure 13-20 Wood and heavy timber beams were
often fire-cut so that a fire-damaged, sagging
floor would simply slide out of the wall pocket
in order to preserve the wall.
36
Type V Wood Frame
  • Most common construction type
  • Homes
  • Newer small businesses
  • Chain hotels
  • Balloon frame versus platform framing
  • Platform framing creates fire stopping
  • Gypsum board protects wood frame members
  • Fires that penetrate wall, floor, attic spaces
    become significant collapse threat

37
Figure 13-21 The wood frame structure, Type V
construction, is the most common type of
construction in North America.
38
Other ConstructionTypes (Hybrids)
  • Methods that do not fit into one of the five
    types
  • Combination of more than one type
  • Other types
  • Lightweight steel frame
  • Insulated concrete formed (ICF)
  • Structural insulated panel (SIP) wall

39
Figure 13-24 This lightweight steel home is
built similar to a Type V. OSB sheeting gives the
steel rigidity to torsional loads such as wind.
40
Relationship of ConstructionType to Occupancy Use
  • Many officials and builders first look at
    anticipated use of building
  • Occupancy classifications
  • Basic arenas
  • Residential
  • Commercial
  • Business
  • Industrial
  • Education

41
Collapse Hazards atStructure Fires
  • Firefighters must understand buildings in their
    jurisdiction
  • Reading buildings is essential to anticipate
    collapse

42
Trusses
  • Truss roof collapses have killed many
    firefighters
  • Come in many styles and shapes
  • Wood trusses commonly used for roof assemblies
    and floor assemblies
  • Steel trusses no less susceptible to collapse
    than wood trusses

43
Figure 13-26 Wood trusses provide a large
surface-to-mass ratio, fuel load, and void
spacesthree of the worst structural collapse
contributors a firefighter will encounter during
structural firefighting operations.
44
Void Spaces
  • Trusses create large void areas
  • Fires are able to spread horizontally
  • Fires can start in void spaces because of
    electrical and utility problems
  • In Type III ordinary construction, voids are
    numerous

45
Roof Structures
  • Flat, pitched, or inverted
  • Many factors determine construction
  • Roof style may allow a large volume of fire to
    develop
  • Some dormers are actually aesthetic and fool
    ventilation crews

46
Figure 13-30 Some common roof framing styles
used in wood frame or ordinary construction.
47
Stairs
  • Believing stairways are durable is a dangerous
    assumption
  • Stairs are built offsite and hung in place with
    metal strapping
  • Stairs are made with lightweight engineered wood
    products
  • Fail quickly when heated

48
Parapet Walls
  • Extension of a wall past top of roof
  • Used to help hide unsightly roof equipment
  • Free standing with little stability
  • Typically collapse when roof starts to sag
  • Historically, dozens of firefighters have been
    killed by collapsing parapets

49
Figure 13-34 This electrical service entrance
and attached sign may be the eccentric load
causing an early failure of this parapet wall.
50
Collapse Warning Signs
  • Factors anticipating collapse
  • Deterioration of mortar joints and masonry
  • Overall age and condition of building
  • Cracks
  • Signs of building repair
  • Large open spans
  • Bulges and bowing of walls
  • Sagging floors
  • Large volume of fire
  • Long firefighting operations

51
Buildings under Construction
  • Especially unsafe during construction,
    remodeling, and restoration
  • Building only meet fire codes when completed
  • Stacked construction materials may overload other
    structural components

52
Time
  • No time limits for firefighting operations
  • Truisms have emerged
  • The lighter the structural element, the faster it
    comes down
  • The heavier the imposed load, the faster it comes
    down
  • Wet (cooled) steel buys time
  • Gravity and time are constant
  • There is no window of time
  • Brown or dark smoke from lightweight structures
    means time is up

53
Preparing for Collapse
  • Incident commander needs to predict collapse
    PROACTIVELY
  • Communicated information between teams help with
    predicting collapse
  • Once occupants have been found, fire control
    should be reduced
  • Firefighters must not wander into collapse zone

54
Figure 13-35 A minimum collapse zone should be
1½ times the height of the building.
55
Lessons Learned
  • Many firefighters have been killed as a result of
    building collapse
  • Firefighters must understand the buildings in
    which they fight fires
  • Knowledge of building construction starts with
    understanding of loads, forces, and materials
  • Five class types are being challenged by new
    construction methods
  • No rule for how long a building will last on fire
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