Building Construction Types

• Factors influencing fire behavior include building and occupancy classification, fuel load, and fire resistance.
• Structures are classified by the materials used in their construction, according to the IBC.
• A 3-digit number code is used: 1st digit for bearing walls, 2nd for structural frames/columns, and 3rd for floor construction.
• There are 5 classifications of building construction.

Type 1 Construction (Fire Resistive)

• Type 1 is the only classification that is not subdivided.
• Walls, columns, and beams have a fire resistance of 2-4 hours.
• Floors have a fire resistance of 2-3 hours.
• Roof decks/supports have a fire resistance of 1-2 hours.
• Interior partitions usually have a fire resistance of 1-2 hours.
• Type 1 construction involves a protected steel frame or reinforced concrete.
• The thickness of insulating material can be adjusted to meet fire ratings.
• Fire-retardant wood can be used in roofs or interior partitions, as per code.
• Steel is non-combustible but not fire-resistive.
• Type 1 buildings are less likely to collapse.
• Combustible materials are only permitted for cosmetics.

Type 2 Construction (Non-Combustible or Protected Non-Combustible)

• Glass and aluminum can be used but have a limited structural role.
• If the roof is 20 ft or more above the floor, a fire-resistive rating can be omitted.
• Type 2A (protected) structural components have 1-hour fire resistance.
• Type 2B (unprotected) unprotected steel is the most common characteristic.
• The failure speed of unprotected steel members depends on ceiling height, size of unprotected members, and fire intensity.

Type 3 Construction (Ordinary Construction, Exterior Walls of Masonry)

• Interior structural components can be either protected or unprotected.
• Type 3A - 2-1-1 includes plaster gypsum board.
• Type 3A - 2-0-0 involves unprotected steel.
• Type 3 can include 2 x 10 floor joists.
• Combustible concealed spaces in Type 3 construction must contain appropriate fire stops.
• Exterior masonry walls will collapse without interior support.

Type 4 Construction (Heavy Timber or "Mill" Construction)

• Does not include subclass.
• The designation 2HH is used in place of a subclass.
• Exterior walls are typically masonry construction, similar to Type 3.
• Involves solid or laminated wood with dimensions greater than Type 3.
• Concealed spaces are not permitted.
• Requires a 6 x 10 inch minimum floor construction, thicker than Types 3 and 5.
• Not normally used for new construction in multistory buildings.
• Common for factories, mills, and warehouses.
• Can be dangerous due to a relatively large amount of fuel present in structural supports.

Type 5 Construction (Wood Frame)

• All major structural components are permitted to be of combustible construction.
• Has 1-hour fire resistance for structural components.
• Extensive concealed spaces are typical.
• Light frame construction is common in small residential and commercial buildings.
• Presents an extreme danger to adjacent structures due to exposure threat.
• IBC limits heights of Type 5 because of exposure threats.

Occupancy Classifications

• IBC has 10 classes.
• NFPA 101 has 12 classes.
• NFPA 101 is a life safety code.
• Mixed occupancies may require a fire wall with a 1-4 hour rating.

Fuel Load

• Fuel load is the total quantity of combustible materials in a compartment.
• Fuel load contributes to the fire load, meaning the maximum amount of heat released if all fuel is consumed.
• Fire load = (weight of combustibles) x (heat of combustion), expressed in pounds per square foot.
• Fire load can estimate the total heat release rate or thermal energy a building will give off if fully involved.
• The faster the available fuel burns, the greater the HRR.
• Non-combustible materials will not ignite, burn, support combustion, or release flammable vapors under anticipated conditions.
• ASTM E 136 is the most common test for determining combustibility.

Fire Resistance

• Fire resistance describes several properties of materials and the ability of a structural assembly to maintain its load-bearing capacity and structural integrity under fire conditions.
• FRR is fire resistive rating.
• FRR is expressed in time units (hours and fractions of hours).
• Walls enclosing an exit stairwell typically have a lower fire resistance rating than columns and floors.
• Laboratory testing is the most common method used to determine fire resistance.
• ASTM E-119 is the standard test.
• Fire testing on building materials dates back to Germany (1884-1886), Denver, Colorado (1890), and New York City (1896).

Structural Design Features

• Force is any interaction that may change the motion of an object.
• Load is any effect that a structure must be designed to resist.
• Stress consists of the factors that work against the strength of apparatus, equipment, or structural support.
• Structures must resist applied loads.
• Loads depend on equilibrium.
• Gravity is the most common load imposed via the weight of the structure's components.
• Additional forces include vibrations, temperature changes, and shrinkage.
• Bending is a reaction within a structural component that opposes a vertical load.

Stresses

• Tension pulls apart.
• Compression squeezes together.
• Shear causes one plane of material to slide past an adjacent plane.

Unique Stresses

• Axial load is applied to the center.
• Eccentric load is perpendicular to the cross-section.
• Torsional load is applied off-center.
• Stress indicators include cracking, crumbling, bending, or breaking.
• Dead loads are fixed in location and quantifiable.
• Live loads are not fixed in location or permanent.
• Static load are steady or applied gradually; dead loads are typically static.
• Dynamic loads involve motion and deliver energy in excess of weight.
• Dynamic loads involve wind, falling objects, and vibration.
• Dynamic load requires the impacted surface to absorb all the kinetic energy to which it is subjected.
• Concentrated loads produce highly localized and non-uniform forces.
• Rain and snow are live loads.

Water related Forces

• Water from firefighting adds additional live load.
• Dynamic load from firefighting is fire flow.
• Static load from firefighting is accumulated water.
• Older multistory industrial buildings have scuppers to drain water through outside walls.
• 250 gallons per minute may impact a target with 2080 pounds of water per minute.
• 3 inches of water adds a static load of 21 pounds per square foot.
• Wind loads exert direct pressure, cause drag, create negative pressure, cause rocking, vibration, and can dislodge objects.

Wind Loads and Beams

• Wind loads by direct pressure are the primary consideration.
• The top flange carries compressive stresses, and the bottom flange carries tensile stresses.
• The web is the neutral axis, where stresses are zero.
• The top and bottom carry most of the load of resisting beams stresses.
• Tall beams support greater loads.
• Columns are designed to support axial loads.
• Columns are not designed to withstand bending stresses.
• Tall thin columns fail by buckling, while short, squat columns fail by crushing.

Arches, Cables, and Trusses

• Arches produce inclined forces and are sometimes designed with hinges, primarily compressive interior stresses.
• Cables bear tension stresses.
• Aluminum cables are lighter than steel.
• Trusses are made of groups of triangles in one plane.
• True trusses are only made of straight members.
• Chords are the top and bottom members of a truss.
• Typical trusses span 22-70 ft, but modern construction trusses can exceed 100 feet.
• Bar joists are lightweight steel trusses.
• Gusset plates are metal or wooden plates used to connect and strengthen joints.
• Space frames are three-dimensional truss structures.
• Load-bearing walls carry compressive loads.
• Frame walls are simply skin do not support anything structurally, but may provide lateral stiffness.
• Studs are placed 12-16 inches apart.
• Post and beam construction carries transverse loads and uses vertical and diagonal elements for support.
• Rigid frames, usually single-story with a gabled roof, are used to transmit bending stress through the joints.
• Rigid frame roofs are hinged to allow slight movement.
• In rigid frames, joints will be the last portion of the rigid assembly to fail under fire conditions.

Other Structural Items

• Slab and column frames include concrete, drop panel, and capital.
• The capital is a broad top surface of a column or pilaster.
• A drop panel increases floor thickness over a column.
• Membrane structures, similar to fabric tents, are designed to be permanent structures over 180 days.
• PTFE (polytetrafluoroethylene) is a fabric weighing less than 2 pounds per square foot.
• Shell structures are three-dimensional with thin components (concrete, cones, domes, barrel vaults, folded plates).

Stairs

• Convenience stairs are not part of egress and are typically only 2 levels.
• Stairs in buildings of 4 or more stories may require a stairway that extends to the roof.
• Stair dimensions include tread (run) and riser.
• Six common types of stairs include straight, return, scissor, circular, folding, and spiral.
• Return stairs involve a landing between floors to reverse direction.
• Scissor stairs are two separate stairs in the same shaft, more space-efficient.
• Circular stairs have a minimum run width of 10 inches.
• Folding stairs are ladders, often found in attic spaces of residential buildings, and have weight limitations.
• Folding stairs may have gas springs (struts) which can fail explosively under sudden exposure.
• Protected stairs must resist the effects of combustion.
• Exterior stairs are naturally ventilated or fully enclosed.
• Fire escapes are not permitted in new construction.
• Smoke proof stair enclosures are designed to limit the penetration of fire.
• Smoke proof stair enclosure: at least one is required in buildings of 5 stories or higher.
• Smoke proof stair enclosures are located on the perimeter of the building and entered through ventilated vestibules/open exterior balconies.
• Active smoke proof designs pressurize upon fire alarm activation.
• Passive smoke proof designs provide smoke ventilation before it enters.
• Open stairs connect no more than 2 adjacent floors above the basement level.

Conveyor and Escalators

• Conveyors are used to transport items and materials.
• Escalators: motor is at upper landing.
• Escalator standard speed is 100 feet per minute.
• Older escalators go at 90-120 feet per minute.
• Escalators often linked with a "step chain".
• Escalators serving more than 2 floors must be protected by sprinklers and draft stops or rolling shutters (18-inch draft stop).
• Elevators: check shaft for smoke
• Types: Passenger, Freight, Service elevators are larger.
• Two most common power types are hydraulic and electric.
• Hydraulic elevators have a 6-floor limit, and no breaks.
• Are attached to a ram, multistage cylinder
• Electric Traction elevators may require a top exit.
• Side or horizontal egress can be missing from hydraulic cars equipped with manual lowering valves.
• Electric elevators use cable and drum or flat polyethylene steel belts.
• Drum elevators are for Passengers, usually have counterweights, found in very old structures, obsolete.
• Traction elevators are for passengers, most common type over 6 stories; have fast speed
• Also use counterweights, 500v AC or DC, brake drum located on the shaft of drive motor.
• A top exit is required on all electric traction elevators.
• AC Traction - breaks are used to aid in directly stopping the car.
• DC Traction - the breaks do not play any part in stopping the car, breaks applied after the car has stopped

Miscellaneous Elevators

• Dumbwaiters are cargo and small freight elevators in restaurants, schools, hospitals, and retirement homes. Machine room less for passengers
• Elevator Safety includes terminal device *terminates power, buffers * pit shock absorbers, speed reducing switch "speed governor”, overspeed switch if speed reducing switch fails, car safety safety jaw that wedge against guide rail to stop free falling car.
• Hoist ways are required to be constructed of fire resistant materials and equipped with fire rated door.

Hoistways and Shafts

• Hoist ways are enclosed on 3 sides with poured concrete.
• Have a 1-2-hour fire rating.
• Elevator shafts used for egress means must be equipped with safety lights.
• A vent at top of elevator shafts prevents “mushrooming” or horizontal spread of smoke.
• A maximum of 3 elevators can be in 1 hoist way.
• 4 or more elevators require a minimum of 2 separate hoistways.
• Express Elevators in Very Tall Buildings are Divided into Zones, that Serve Upper Floors 15-20 Levels at a Time.
• These have No Stop Between First Floor and Upper Floor Landing.
• Rescue Doors are placed every 3 floors.

Double Decker and Interlocks

• Double decker elevator serves odd floors on the bottom level and even floors on the top level.
• Electric interlocks keep doors from opening if they are not level with the floor
• Side or Horizontal egress require electrical interlocks if doors are operated, if activated will automatically stop the car.
• Door clutches act as car door safety measures
• Refuse Chutes require sprinklers at the top and bottom

HVAC systems

• HVAC systems create and maintain comfortable environments.
• HVAC systems may have become life support systems in more complex buildings.
• Cupolas are rooftop projections used for ventilation and lighting; used for vertical cooling and airflow through buildings

HVAC Fans

• HVAC FANS require separate fans for supply and exhaust.
• Duct detectors are installed for fans exceeding 2000 cubic feet per minute.
• Butane and Propane may be used in air heating and cooling systems, which pose a hazard to firefighters.
• Smoke dampers restrict smoke flow and are usually activated by the fire alarm system.
• Fire dampers restrict airflow and are automatically activated by fire alarm signaling fusible links.
• Forced Air systems enclosures of hvac be 1 hour in buildings less the 4 stores, 2 hours in building 4 stories or greater.

Miscellaneous HVAC

• Hydronic Systems transfer heat using water; have cooling towers
• Hurricane glazing on glass is difficult to ventilate and remove
• HVAC may be placed in smoke control mode automatically or manually, but manually takes priority, at the Firefighter Smoke Control Station (FSCS), to prevent recirculation
• Pressure sandwich creates a “pressure sandwich” by providing continuous supply of air to the non fire floors creating higher air pressure on floors above and below the fire floors, reducing movement of smoke into those areas VENTS (theaters are required to have smoke vents above stage).
• Vents come as single or double leaf metal doors, or plastic domes designed to open manually or automatically and must open a minimum of 4 feet in either direction.
• Vents are less effective when used in conjunction with sprinklers.
• Smoke towers, or Smokeproof enclosures, are escape stairways that exit directly to a public way.
• Curtain Boards should not be less than 20% of the ceiling height
• Draft Curtains are spaced out so be no farther than 8 times the ceiling height
• Pressurized stairwells can either be single injection with one fan or multiple injection with one fan and several discharge points along the shaft.
• High voltage is 600 plus volts, low voltage less than 600 volts

Transformers and Generators

• Transformers convert high voltage to appropriate voltage.
• Rooms or vaults Inside and with sprinklers - 1 hour fire rating, and no sprinklers - 3 hour fire rating
• Transformers generate heat, should be protected with sprinklers if able
• Transformer cooling: oil and air; located at or near grade;
• Air cooled transformers = "dry transformers".
• Oil cooled transformers = oil needs to have dielectric properties, required to be labeled, and can contain PCBS.
• Generators used must be able to maintain life safety equipment at a bare minimum: 2-4 hours, hospitals up to 48 hours or longer
• There is a limit to the amount of fuel tanks can hold: 60 gallons