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Structural Collapse during firefighting can be expected to increase. Three factors are:
Age of buildings, abandonment and lightweight construction material, will increase the number of burning building collapse
A building, like a person, has a life span of
seventy-five or a hundred year
Over the past two decades, abandonment of buildings in the Northeast adn Midwest has
increase the collapse danger to firefighters
Very few person, other than firefighters,
are killed by burning buildings collapse, only firefighters are close to a burning building when it has been weakened by flames to the point of collapse danger.
When a burning building collapse kills or seriously injures a firefighter,
a post fire investigation and analysis should be conducted.
- A curved masonry structure used as a support over an open space.
- The removal or destruction of any part of an arch will cause the entire arch to collapse.
Three basic methods of construction
- 1. Balloon
- 2. Brace Frame
- 3. Platform
- 1. Exterior walls have studs extending continuously from the structure's foundation sill to the top near the attic.
- 2. Concealed space between these studs can spread, fire, smoke, and heat from the cellar area, or the intermediate floors to the attic space.
- 3. If a non-bearing wall collapse during a fire, the continuous studs will cause the wall to fall straight outward, in one section, at a 90-degree angle.
- 4. If the bearing wall collapse it can cause a second collapse of the floors it supports
A horizontal structural member, subject to compression, tension, and shear, support by one of three methods.
Cantilever Beam Support
- A beam supported or anchored at only one end, which is considered a collapse hazard during fire exposure.
- Examples: ornamental stone cornice, a marquee, a canopy, a fire escape, and an advertising sign attached perpendicularly to a wall.
- It has the least amount of structural stability during a fire.
Continuous Beam Support
- A beam supported at both ends and at the center.
- During a fire, it has the greater structural stability
Simple Support Beam
- A beam supported at both ends
- If the deflection at the center of such a beam becomes excessive, a collapse may occur
- A simple supported beam is more stable under fire conditions than a cantilever beam but less than a continuous supported beam.
Brace Fame Construction
- Sometimes called "post and girt" construction. Vertical timbers called posts reinforce each of the four corners of the structure, and horizontal timbers call girts reinforce each floor level
- Posts and girts are connected by fastening called mortise and tenon joist
- During a fire walls often fails in an inward/outward collapse. The walls break apart with the top collapsing inward on top of the pancaked floors, and the bottom part collapsing outward on to the street.
- A wall reinforcement or braced build on the outside of a structure, sometimes call a "wall column".
- On masonry wall, a buttress is a column of bricks built into the wall.
- When separated from the wall and connected by an arch at the top, it is called a flying buttress.
- The presence on an exterior wall can indicate the point where roof trusses or girders are supported by a bearing wall.
- A buttress on the inside of a wall is called a pilaster.
- The failure of any portion of a structure during a fire
- A section of falling plaster ceiling, a broken fire escape step, a falling coping stone and the collapse of several tons of brick walls are all structural failures and should be classified as structural collapse.
Curtain Fall Wall Collapse
- Occurs when an exterior masonry wall drops like a falling curtain cut loose at the top.
- THe collapse of a brick veneer, b rick cavity, or masonry backed stone wall often occurs in a curtain fall manner.
- The impact of an aerial platform master stream striking a veneer wall at close range can cause a curtain fall collapse of bricks.
- The collapse of an exterior wall that breaks apart horizontally. The top collapse inward, back on top of the structure, the bottom collapse outward on to the street.
- Wood brace frame constructed building collapse in this manner, and a timber truss roof collapse can cause a secondary collapse of a front wall in this manner.
Lean Over Collapse
A type of wood frame building collapse indicated by the burning structure slowly starting to tilt or lean over to one side.
Lean to Floor Collapse
- A floor collapse in which one end of the floor beams remains partially supported by the bearing wall, and the other end of the floor beams collapses on the floor below or collapse but remains unsupported.
- A lean to collapse can be classified as supported or unsupported, depending upon the position fo the collapsed beam ends.
Ninety Degree Angle Wall Collapse
- A type of burning building wall collapse. The wall falls straight out as a monolithic piece at a 90 degree angle, similar to a falling tree.
- The top of the falling wall strikes the ground a distance from the base of the wall that is equal to the height of the fall section.
- Bricks or steel lintels may bounce or roll out beyond this distance.
Pancake Floor Collapse
- The collapse of one floor section down upon the floor below in a flat, pancake like configuration.
- When floor beams pull loose or collapse at both ends, a pancake collapse occurs.
The collapse of portions of burning taller structures on to smaller structures, causing the collapse of the smaller building.
Tent Floor Collapse
- A floor collapse in the shape of a tent.
- When a floor collapse and an interior partition or wall holds up the center of the fallen floor, a tent floor collapse occurs.
V Shape Floor Collapse
- The collapse of a floor a the center of the floor beams.
- The broken center of the floor section collapse down upon the floor below, and both ends of the floor section remain partially supported or rest up against the outer bearing walls.
A vertical structural member subject to compressive forces.
Columns and bearing walls
Girders and beams
- The top masonry tile or stone of a parapet wall, designed to carry off rainwater. Sometimes called a "capstone", it weighs between five and fifty pounds.
- A coping stone can be dislodged and fall from a parapet under the impact of a high pressure master stream or when struck by a retracting aerial ladder or aerial platform.
- A bracket or extension of masonry that projects from a masonry wall.
- It can be a decorative ornament on the top of a parapet front wall,or it can be used on the inside of a brick wall as a support for a roof beam end.
Corbel Ledge or Corbel Shelf
- Used on the inside of a masonry wall to support a beam.
- Under a weigh of a firefighter, a roof beam end that is resting on corbel ledge can roteate off its support if the center of the beam has been burned away.
A horizontal surface covering supported by a floor or a roof beam
A bend, twist, or curve of a structural element under a load.
The front or face of a building
Fire Cut Beam
A gravity support beam end designed to release itself from the masonry wall during a collapse.
The measure of maximum heat release when all combustible material in a given area is burned.
The cause of a motion, a change in motion, or a stoppage of motion.
- Dead Load
- Live Load
- Wind Load
- Impact Load
- Also know as Load Stress
- Compressive stress
- Tension stress
- Shear stress
A structural member that supports a floor or roof beam.
Primary Structural Members
- Bearing Walls
A metal fastener in the form of a flat plate used to connect structural members
- A support used to reinforce an opening in the floor of a wood frame, ordinary, or heavy timber building.
- Placed between two trimmer beams and supports the shorter cut off beams called tail beams
Hierarchy of Building Elements
Horizontal and vertical structural elements fo a building arranged in collapse hierarchy.
- Hierarchy of Collapse
- Structural Framing Seriousness
- Decks Less
- Beams/Floors and roofs |
- Girders |
- Columns v
- Bearing Walls More
- A piece of lumber used as a floor or roof beam.
- The term joist, beam and rafter are used interchangeable.
- Supports a roof or floor deck and is ofter supported by a girder.
- One KIP equals a thousand pounds
- KIP is used to simplify the figures
- K.S.I. = KIPS per square inch
- A horizontal pieces of timber, stone, or steel placed over an opening in a wall.
- A load bearing structural element that supports and redistributes the load above the opening
Forces acting upon a structural
Passes through the center of a structural and is the most efficient manner by which a load can be transmitted through a structural support like a column or a bearing wall.
A load applied at one point or within a limited area of a structural.
A static or fixed load created by the structure itself and all permanent equipment within.
A load transmitted off center or unevenly through a structural members.
A load applied to a structure suddenly, such as a shock wave or vibrating load.
Any type of load applied to an upright structure from a direction parallel to the ground.
A transient or movable load, such as a building's content, the occupants, the weight of firefighters, the weight of fire equipment, and the water discharge from hose streams
A load the remains constant, applied slowly.
A load that creates a twisting stress on a structural member.
A lateral load imposed on a structural by wind.
A structural connection often used in braced wood from construction, it is a hole cut into a timber that receives a tenon.
Open Web Steel Bar Joists
- A lightweight steel truss used as a floor or roof beam. It is made from a steel bar, bent a 90 degree angles, welded between angle irons at the top and bottom bar bends.
- Used for floor and roof beams in non combustible buildings
- A masonry column bonded to adn build as an integral part of the inside of a masonry wall.
- Can carry the load of a girder or timber, or it can be designed to provide lateral support to a wall
Platform Wood Frame Construction
A building of this construction has one complete level of two by four inch wood enclosing walls raised and nailed together, the floor beams and deck for the next level are constructed on top of these walls. The next level of two by four inch wood enclosing wall are then constructed on top of the first competed level.
Primary Structural Member
A structure that supports another structural member in the same building, such as a bearing wall, a column, or a girder.
Restrained Beam End
A welded, nailed, bolted or cemented end of a floor or roof beam.
A horizontal timber that frames the highest point of a peak roof. Roof rafters are fasten to the ridgepole.
the sheltering structure of a building that protects the interior spaces from natural elements
The quotient of the load that will cause a structure ot collapse divided by the load as structure is designed to support.
- A force exerted upon a structural member that strains or deforms its shape.
- Stress and load are often used interchangeability.
A force pressing or squeezing a structure together.
A stress causing a structure ot collapse when contacting parts or layers of the structure slide pass on another.
Stress placed on a structural members by the pull of forces causing extension.
A ceiling built several inches or feet below the supporting roof or floor beams above, sometimes called a "hanging" or "dropped" ceiling.
The concealed space above the ceiling.
A projecting, reduced portion of a timber designed to be inserted into the mortise hole of another timber.
- A polished floor covering made of small marble chips set in several inches of cement.
- It adds weight to floor beam, conceals the heat of serious fire below, and, because it is watertight, allows water to accumulate and build up to dangerous proportions.
A wood beam constructed around the perimeter of a floor opening. A trimmer beam supports the header beam, which in turns supports the tail beams
- A brace arrangement of steel or wood frame work made with triangular connecting members.
- They suffer early collapse during a fire because it exposed surface area is greater than the exposed surface area of a solid beam spanning the same distance.
- Truss roof beams are spaced farther apart than solid beams, creating large areas of unsupported roof deck.
Three Common Types of Trusses
- Parallel Chord
Types of Walls
- Area Wall
- Bearing Wall
- Fire Wall
- Free-Standing Wall
- Parapet Wall
- Party Wall
- Spandrel Wall
- Veneer Wall
A free standing masonry wall surrounding or partly surrounding an area.
- An interior or exterior wall that supports a load in addition to its own weight.
- Most often supports the floors and roof of a building.
A non bearing, self supporting wall designed to prevent the passage of fire from one side to another.
Free Standing Wall
A wall exposed to the elements on both sides and the top, such as a parapet wall, a property enclosing wall, an area wall, and a newly constructed exterior wall left standing without roof beams or floors.
- The continuation of a party wall, an exterior wall, or a fire wall above the roof line.
- Are considered free standing walls
A bearing wall that supports floors and roofs of two buildings.
That portion of an interior wall between the top of one window opening and the bottom of another.
A finished or facing bricks or stone wall used on the outside of a building.
Type of Wall
- Free Standing Wall
- Non Bearing Wall
- Bearing Wall
Less to More
Horizontal Collapse Zone
The horizontal measurement of the wall. When establishing a collapses zone, estimate this measurement in addition to the outward area that the wall may cover if it falls.
Vertical Collapse Zone
- The expected ground area that a falling wall will cover when it collapses.
- Generally that distance away from the wall equal to the height of the wall.
- Heavy stones will fall farther than this distance.
Five construction types when considering collapse or fire resistance of buildings
- 1. Fire Resistive construction
- 2. non combustible/limited combustible construction
- 3. ordinary brick-and-joist construction
- 4. heavy timber construction
- 5. wood-frame construction
Major problem in a fire-resistive building and why
- Central air conditioning system
- In a structure with a central air conditioning system, every fire barrier in the building is penetrated
- The entire building may be interconnected by a network of holes, concealed spaces and voids through which flame and smoke can spread
Problem associated with non combustible/limited combustible building
The flat, steel roof deck covering that can ignite during a fire
Major fire problem in an ordinary constructed building
fire and smoke spread throughout concealed spaces
Unlike concealed spaces in fire resistive or non combustible buildings, those in ordinary constructed buildings contain large amounts of
combustible material in the form of wood lath, wood furring strips, cross bridging, wood joist, and wood two by four wall studding
In a ordinary constructed building most serious concealed space is
the common cockloft.
For a building to qualify as heavy timber construction
a wood column cannot be less than eight inches thick in any dimension and a wood girder cannot be less than six inches thick
The major fire problem of this brick enclosed timber structure is
The large wooden interior timber framework
Wood Frame construction is the only one of the five types with
combustible exterior walls
Seven sides of the fire area in a wood frame constructed building
- 1. above the fire
- 2. below the fire
- 3. the four sides of the fire
- 4. combustible exterior walls
2 basic types of fire resistive construction
- Reinforced concrete buildings
- Structural steel building
Of the five construction types, fire resistive buildings are
the most stable and have the best collapse record.
A fire resistive building does suffer structural failure during serious fires, and it collapse danger lies in concrete.
- Reinforced concrete buildings, heated concrete ceiling collapse on top of FF
- Steel skeleton building concrete floors explode upward
The rapid expansion of heated moisture inside the concrete.
Nation's most widely used construction type
Non Combustible/limited combustible construction
Three basic types of Non Combustible construction
- 1. Metal frame structure covered by metal exterior walls
- 2. Metal frame structure enclosed by concrete block
- 3. Non bearing walls; the concrete block bearing walls supporting a metal roof structure
the collapse danger to a FF from a non combustible building is
roof cave in, the collapsing material, the unprotected steel open web bar joist.
The main advantage of the lightweight steel roof support is
The non combustibility - the bar joist does not add fuel to the fire
Has exterior bearing walls of masonry with wood floor and roof
Ordinary constructed building called "brick and joist"
The structural hazard of an ordinary constructed building is
the parapet wall, the portion of the masonry wall that extends above the roof level.
The hazards of heavy timber building
Falling masonry walls which crash to the ground and spray chunks of bricks and mortar along the street or payment.
The structural hazard of a wood frame building
is the combustible bearing wall constructed of two by four inch wall studs
3 ways a masonry exterior building wall by collapse
- 1. 90 degree angle
- 2. Curtain fall
- 3. Inward/outward collapse
Wood joist floor system can collapse in 3 different ways when attacked by fire
- 1. Only the wood deck burns through
- 2. Several floor joist may fail, causing a localized failure of a section of a floor
- 3. A large section or the entire floor level, sometimes triggering the subsequent collapse of floors below or enclosing walls
One room in a residential building which frequently subject to floor joist collapse is
Several reasons why floor joist collapse in bathroom
- Bathroom room fixtures - dead load or static fix load
- Finished tile floor
- Fire destruction and rotting
3 most common types of sloping roofs are
- 1. gable roof
- 2 hip roof
- 3. gambrel roof
Type of roof with sides sloping up from 2 walls
Type of roof with sides sloping up from four walls
Type of roof with 2 slopes on each of two sides, with the lower slope streeper than the upper
Primary structural members of a flat roof
2 - two bearing walls
Primary structural members gable roof
3 - Two bearing walls and one ridge rafter
Primary Structural members of Hip Roof
7 - Two bearing walls, one ridge rafter and four hip rafters.
3 most common types of wood construction used for sloping roofs
- 1. Timber truss
- 2. Plank and beam
- 3. rafter construction
What is a timber truss
- Timber is a wooden construction larger than two by fours finches but not large enough to be classified as heavy timber or mill construction.
- truss is a structural composition of a large wooden members joined together in a group of triangle and arranged in a single plane so loads applied at points of intersecting members will cause only direct stress
Most common type of timber truss
3 Common types of suspended ceilings
- 1. Wood grid system with permanently affixed ceiling
- 2. Metal grid system with a permanently affixed ceiling
- 3. Lightweight metal grid system with a removable panel ceiling.
Least hazardous type of suspended ceiling to FF
Lightweight metal grid system with removable ceiling panels
Most Hazardous type of suspended ceiling to FF
Wood grid system with permanently affixed ceiling or metal grid system iwth permanently affixed ceiling
3 basic stair types
- 1. Straight Run
- 2. U - return stair
- 3. L - shape stair
3 ways in which a wood frame building can collapse
- 1. 90 degree angle
- 2. Lean over and collapse
- 3. All four wood enclosing walls may crack apart and fall in a inward/outward collapse