CHAPTER 13 Copyright © 2007 Thomson Delmar Learning 13.1 Building Construction.

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13.1Copyright © 2007 Thomson Delmar Learning

Building Construction

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Objectives (1 of 2)

• Describe the relationship between loads, imposition of loads, and forces.

• List and define four structural elements. • Identify the effects of fire on five common building

materials. • List and define the five general types of building

construction.• List and define hazards associated with alternative

building construction types

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Objectives (2 of 2)

• List five building collapse hazards associated with fire suppression operations.

• List five indicators of collapse or structural failure that might be found during fire suppression operations.

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Introduction

• Collapse of burning buildings has killed and injured many firefighters engaged in aggressive fireground operations.

• Firefighters must understand building construction from the perspective of assembly methods, materials used, and how buildings react to heat and fire.

• Understanding building construction requires a long-term commitment to study and research.

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Building Construction Loads and Forces

• There are two basics types of loads: live and dead.– Further description includes impact loads and

distributed loads. • Fire load is a fire service term.• Loads can be imposed axial, eccentric, or

tensional.• Loads create a force within the material.

– Forces include compression, tension, and shear.– Gravity is primary collapse force.

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Structural Elements (1 of 2)

• Beams, columns, and walls.– Beams distribute loads perpendicular to the

load.– Beams consist of a top chord, bottom chord,

and web.– Top chords are usually under compression.– Bottom chords are typically under tensile

force.– A truss is a beam formed by geometric

triangles.

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Structural Elements (2 of 2)

• Columns are elements under compression.• Walls are a form of column.

– They may be load bearing or not.

• Connection points transfer the load from columns and beams.

• Connection points are usually the weak link in fire conditions.

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Fire Effects on Building Materials

• Construction materials are chosen based on many factors.– Cost– Quality– Suitability

• Fire resilience may be considered.

• Advanced technology may change materials found in construction.

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Fire Effects on Building Materials—Wood

• Wood is the most common material used.– Adds to fire load.– May lead to increased instability during fire.

• The mass of the wood affects its strength when exposed to fire.

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Fire Effects on Building Materials—Steel

• Excellent shear, tensile, and compression strength.

• When heated, expands and becomes more pliable.

• Structural steel loses 50% of strength at 1100° Fahrenheit.

• Steel will buckle when unable to expand.• Important to keep cool under fire conditions.

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Fire Effects on Building Materials—Concrete

• It is a mixture of Portland cement, sand, water, and gravel.

• Steel can be added for strength.

• Moisture may cause “spalling” when heated.

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Fire Effects on Building Materials—Masonry

• Term used for block, brick, and tile materials

• May be load bearing or veneer

• Excellent fire resistance except for mortar which may fail quickly under fire conditions

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Fire Effects on Building Materials—Composites

• Composites challenge firefighters in determining fire resilience.

• Lightweight wooden I beams made from wood chips and glue will fail quickly in a fire.

• Plastics are used to reinforce other materials.

• Oriented strand board (OSB) and polystyrene are strong, but fail quickly when heated.

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Types of Building Construction

• There are five broad categories.

• Renovations may have multiple types of construction.

• Fire ratings are designed to give occupants more time to escape.

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Type I: Fire-Resistive Construction

• It is designed to stop spread of fire from one area to another.

• Steel and concrete used for structural members.

• There is a three- to four-hour fire resistive requirement.

• Fire may spread through broken windows, elevator shafts, and utility runs.

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Type II: NoncombustibleConstruction

• Steel is the primary material used.

• It may have combustible contents causing fire spread.

• Suburban strip malls are typically Type II construction.

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Type III: Ordinary Construction

• Masonry walls with wood roofs and floors

• May have many void spaces for fire spread

• Sagging floors of older buildings reinforced with steel rods

• Floor beams, typically “gravity” fit, may fail quickly when floors sag

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Type IV: Heavy Timber Construction

• Thick masonry walls with large dimension lumber for floors and roofs.

• Few void spaces, but many open spaces.

• Floors will collapse when sagging leaving walls unsupported.

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Type V: Frame Construction• The wood frame is most

common.• It may be “balloon frame”

or “platform.”• Newer lightweight

buildings are like a “horizontal balloon frame”.

• It is protected from fire by covering with gypsum board.

• Brick veneers may be frame construction.

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Other Construction Types

• Newer methods may not fit into the five general areas..

• Lightweight steel frame looks like wood frame.

• Insulated concrete forms use expanded polystyrene blocks to make forms that are poured, very flammable when gypsum board fails.

• Manufactured buildings are low mass causing rapid fire spread.

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Construction Type to Occupancy Use

• Anticipated use determines occupancy classification.• Common classifications

– Residential– Commercial– Business– Industrial– Hazardous– Educational

• Classification will help firefighters understand specific fire problems.

• Buildings constructed under one type may have been converted to different use.

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Collapse Hazards at Structure Fires

• Firefighters need to preplan buildings in their jurisdictions.

• Understanding the signs of stress or failure is critical.

• Identifying potential collapse zones is critical.

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Collapse Hazards at Structure Fires—Trusses• Truss roof collapses have killed and injured many

firefighters.• Trusses are beams that use triangles of lumber to

replace mass.• Failure of a single part will cause entire truss to fail.• Failure of a single truss may lead to multiple truss

failures.• Gusset plates used to join wood components absorb

heat faster than the wood.• Steel trusses have a high surface to mass ratio.• An open web steel truss is called a bar joist.

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Parallel Chord Truss

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Open Web Steel Joists

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Wood Trusses

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Collapse Hazards at Structure Fires—Void Spaces

• Trusses create large void spaces that allow fire travel.

• Fire in void spaces may go undetected causing rapid fire spread.

• Void spaces may penetrate multiple buildings that share walls.

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Truss Construction Void Spaces

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Collapse Hazards at Structure Fires—Roof Structures

• There are multiple types of roof shapes.• May hide heavy HVAC and utility equipment

on roof.• Roof style may allow for large volumes of fire.• Mansard roofs have many concealed spaces.• Dormers may be ornamental or actual living

space.

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Collapse Hazards at Structure Fires—Stairs

• Stairs are critical avenues for firefighters to make rescues and reach the fire.

• Older buildings use durable, high mass stairs.• New buildings use lighter weight stairs built

off site with low mass materials.• Engineered wood and plastics are used and

may cause failure before other structural members.

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Collapse Hazards at Structure Fires—Signs

• Waiting for visual indicators is dangerous; rely on construction knowledge and preplanning.

• Factors and visual indicators that may assist in predicting a collapse:• Age of building• Cracks• Presence of tie rods• Open spans• Sagging floors• Smoke from cracks• Bulging walls

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Collapse Hazards at Structure Fires—Buildings Under

Construction • Unsafe during construction, remodeling, and

restoration.• Must meet fire and life safety codes only when

complete and occupancy permit issued.• Protective features may be missing, incomplete,

or out of service.• Stacked construction material may overload

structural elements.

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Collapse Hazards at Structure Fires—Preparing for Collapse

• After initial search activities, risk vs. benefit must be considered for property.

• Defensive (exterior) firefighting activities are still dangerous if in a collapse zone.

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Parapet Wall Collapse

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Summary• Firefighters must know and understand building

construction.• Understand the different materials used and tactics

for firefighting.• Understand the possibility of multiple types of

construction due to renovation.• Understand construction methods and identify the

weakness that may cause collapse.• Firefighters need to work toward safe fireground

operations.

CHAPTER 13 Copyright © 2007 Thomson Delmar Learning 13.1 Building Construction.

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Transcript of CHAPTER 13 Copyright © 2007 Thomson Delmar Learning 13.1 Building Construction.