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Building Construction Essay

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Paper type: Essay

The 3 model codes are in the process of developing a single code package called the International Building Code (IBC). Included in this package is the International Fire Code (IFC). The IBC/IFC will be promulgated by the International Code Counsel (ICC): • Uniform Building Code (UBC), published by the International Counsel of Building Officials (ICBO)…Includes the Uniform Fire Code (UFC) • Standard Building Code, published by Southern Building Code Congress International…includes the Standard Fire Prevention Code. • BOCA, National Building Code…Includes the BOCA National Fire Prevention Code.The design process involves compromises & a prioritization of objectives. Cost is always a major concern and frequently necessitates a reduction of plans. The final design always involves a balancing of what is desired, what is needed, and what is practical. Fast tracking – the design & construction phases overlap to reduce total construction time. Inspection – involves the verification that the proper materials & construction techniques are used Testing – performed on certain materials, systems, and components such as concrete, fire pumps, and emergency generators.The usual role of the Fire Inspector is to ensure proper installation & operation of fire protection systems. Chapter 3: Building Classifications To the FF, the most significant building characteristic is how the building can be expected to behave under fire conditions. Fire resistance – a collective property of materials & assemblies…the ability of a structural assembly to maintain its load bearing ability under fire conditions. The properties of the materials include: • Combustibility • Thermal conductivity • Chemical composition • Density • DimensionsFire resistance rating – the quantitatively evaluated fire resistance of the structural components. The rating is determined by test procedures simulating fire conditions & is expressed in hours. Fire resistance for structural elements such as: • Beams • Columns • Walls & partitions • Floor & ceiling assemblies • Roof & ceiling assemblies It is necessary to erect assemblies in the field exactly as they are tested in the laboratories so that the ratings are obtained. To determine fire-resistance ratings, the component is subject to the heat of a fire in a test furnace.The procedure is described in NFPA 251, Standard Methods of Fire Tests of Building Construction & Materials (also American Society for Testing & Materials [ASTM] E-119). When a structural specimen is tested, the test is conducted until either the specimen fails or the specified endurance for which the specimen is being tested is reached. Best known testing laboratory is UL, Fire Resistance Directory. Fire-resistance ratings are expressed in certain standard intervals: • 20 min. • 45 min. • 1 hr • 2hr • 3 hr • 4hrFire resistance ratings for floor & ceiling assemblies are rated by both: • Restrained assemblies – affect the extent that an assembly may expand or rotate at its ends when exposed to high temperatures. • Unrestrained assemblies Fire testing has been going on for years. In recent years, mathematical equations have been used to predict the behavior of materials at high temperatures. Building codes usually make use of fire-resistance ratings based on the standard test. Computer models can deal with more realistic fire behavior of materials than the traditional standard time & temperature test procedure.Noncombustible material – in the form in which it is used and under the conditions anticipated, will not ignite, burn, support combustion, or release flammable vapors when subjected to fire or heat. The most commonly used test for determining combustibility is ASTM E 136, Standard Test Methods for Behavior of Materials in a Vertical Tube Furnace at 750? C. NFPA 220, Standard on Types of Building Construction, have 3-digit code designations: • 1st digit – rating of exterior bearing walls • 2nd digit – rating of structural frames or columns and girders that support loads of more than one floor. 3rd digit – rating of floor construction. Most codes will not allow a wood-frame school to be more than One-story in height. occupancy classifications. They are as follows: National Fire Protection Association (NFPA 101 Life Safety Code & NFPA 220 Standard on Types of Building Construction). & the International Code Council (ICC) National Fire Protection Association The five types of building construction are: Type I – the least combustible building type and considered to be “fire-resistive”. The two most common methods of constructing Type I buildings are by using reinforced concrete or a protected steel frame.The structural members (walls, floors, columns, beams, and roof) are constructed of non-combustible or limited combustible materials that have a specified fire resistance.. These non-combustible materials are defined by the building code that is adopted. The primary fuel load is composed of the contents of the structure. • Bearing walls, columns, & beams a fire-resistance rating of 3-4 hrs • Floor construction 2-3 hrs • Floor construction 1-2 hrs • Partitions usually 1-2 hrs Type II – is similar to type I in construction. Theses buildings are considered “non-combustible or limited combustible” construction.The structural members are allowed to be at a lower fire rating than type I buildings. Type II Construction can be either protected or unprotected. In unprotected construction, the major components are noncombustible but have no fire resistance. Unprotected steel is the most common characteristic in unprotected, noncombustible construction the sub classifications: 222 & 111, have structural components with one or two fire-resistance ratings; 000 have no fire-resistant requirements. Roofs are often flat, built-up types that may contain combustible felt.The primary fuel load is composed of the contents of the structure. Type III – is also known as “ordinary construction”. The exterior bearing walls are constructed of “non-combustible or limited combustible” construction normally masonry. The interior structural members (walls, columns, floors, beams, and roofs) are constructed of wood or some other combustible material. Combustible interior materials are protected by insulating materials such as plaster or gypsum board. The adopted building code specifies the fire rating required for these materials.A fire concern is the spreading of smoke/fire through concealed spaces. Type IV – is referred to as “heavy timber” construction. The exterior walls are constructed to the same specifications as type III (normally masonry), but the interior structural members (arches, columns, floors, beams, and roofs) are constructed of solid or laminated wood without concealed spaces. The primary fire hazard is the massive amount of fuel presented by the large structural members in addition to the buildings contents. Building codes will require a minimum dimension on all columns and beams (usually at least 8”).Type V- is the most combustible type of construction. It is also referred to as “wood-frame construction”. The exterior walls, bearing walls, floors, roofs, and supports are constructed of wood or some other approved combustible. The materials used are the same as those approved for type IV, but are allowed to be in smaller dimensions. There are more voids & channels than found in type III. Some Type V buildings have a brick veneer, but are reliant upon the wood framing for structural support. Brick veneer adds little fire resistance, except for a possible reduction in communication between buildings.Free standing structures usually up to 6-stories in height. • Requires 1-hr fire-resistance rating for all structural elements. Normally accomplished by covering with plaster or fire-rated gypsum board. • May have non-rated structural elements International Code Council (ICC) Type I – the least combustible building type. Characterized by the use of steel, iron, concrete, or masonry structural elements: • Type IA o 3-hr resistance rating to structural frame & load bearing walls o 2-hr resistance rating of floors o 1 ? hr resistance rating of the roof • Type IB 2-hr resistance rating to structural frame & load bearing walls o 2-hr resistance rating of floors o 1-hr resistance rating of the roof Type II – often referred to as a “1-hr building”. The structural members are allowed to be at a lower fire rating than type I buildings • Type IIA – similar to Type I in structural elements being steel, concrete, or masonry. 2-hr fire resistance on floors. • Type IIB – Requires approved noncombustible materials, but the materials may have no assigned fire-resistance rating. Type III – Exterior bearing walls must have a 2-hr fire resistance rating. Type IIIA – requires materials with a 1-hr fire resistance throughout the structure. • Type IIIB – Lacks 1-hr fire-resistance rating Type IV – exterior walls constructed of noncombustible materials, while the interior building elements are constructed of solid or laminate wood having no concealed spaces • Exterior walls – may have fire retardant treated wood framing with 2-hr fire resistance rating or less. • Wooden columns – Requires min. 8” dimensioned lumber • Floor framing – requires sawn or glued-laminated timber of at least 6” nominal depth & not less than 10” depth. Roof framing – wood-frame or glued laminated arches. Minimum of 6” nominal width & 8” nominal depth for the first half of its length…then no less than 6” nominal dimension for the top half of its length. • Roofs – no concealed spaces Type V – structural, exterior, and interior walls constructed of any material permitted by code. • Type VA – requires 1-hr fire-resistance rating for all structural elements except nonbearing interior walls & partitions. • Type VB – May have non-rated structural elements Chapter 4: Structural PrinciplesThe magnitude of forces acting on a building is the most critical aspect of engineering design, and the ability to evaluate these forces is what distinguishes a casual knowledge of buildings from a professional knowledge. Load – any effect which a structure must be designed to resist: • Gravity • Wind o Direct pressure – impact of wind on a surface (primary effect considered) o Drag – fluid effect of wind as it moves along a surface o Negative pressure – suction effect produced on downwind side o Secondary effects Rocking – due to variations in wind velocity ? Vibration – due to harmonics of building ? Clean-off effect – moving air blowing objects off building • Earthquakes – create lateral shaking forces that are the most damaging • Soil pressure o Active pressure – pressure exerted against the foundation o Passive pressure – force of foundation against the soil Live load – any load not fixed or permanent • Contents • Snow • Rain Dead load – weight of any permanent part of a building • Roofs • Floor slabs/decks • Interior/exterior walls • Stair systems • Columns Permanent equipment (elevators, HVAC, pumps) Concentrated load – applied at one point or over a small area. *Water has a density of 62. 4 pounds per cubic foot Static load – steady or applied gradually (dead load of a building, snow load & many live loads. Dynamic loads – involve motion…wind, moving vehicles, earthquakes, vibrations, & falling objects. Differ from static loads in that they deliver energy in addition to weight. Structural Equilibrium & Reactions: Equilibrium – the support provided by a structure is equal to the applied loads. Reactions – forces that resist the applied loads.Exterior loads can create different kinds of interior forces in materials: • Tension – pulls apart • Compression – squeeze (concrete has good compressive strength but little tensile strength). Exterior bearing walls • Shear – slide one plane past an adjacent plane Stress – a measurement of force intensity and is expressed as force units divided by the area over which the force is applied. Exterior loads are classified as: ? Axial ? Eccentric ? Torsional Structural Components: • Beam – a structural member that can carry loads perpendicular to its longitudinal dimension.Primary design is their ability to resist bending from the applied loads. • Column – designed to support an axial compressive load • Arches – curved structure in which the interior stresses are primarily compressive. Arches develop inclined reactions in their supports. • Cables – flexible & are tension stresses • Trusses – framed structural units made of groups of triangles in one plane. A true truss is only made up of straight members. 22 – 70 ft • Space frames – 3-dimensional truss structures Chapter 6: FoundationsAll buildings settle to some extent due to the compaction of the soil: • Uniform settlement • Differential settlement o Downward/settlement o Upward/heaving o Lateral displacement/outward Foundation Types: • Shallow – transfers weight of the building to the soil at the base of the building. Typically use footings to transmit load to the soil o Wall footing – continuous strip of concrete that supports a wall o Column footing – square pad that supports a column o Grillage footing – consists of layers of beams placed at right angles to each other & usually encased in concrete. Deep – penetrate the soil directly under a building to reach soil at a greater depth that can support weight of building. A high-rise building requires a foundation that extends 100 ft or more. o Piles – driven into the ground & develop their load carrying ability through friction with the surrounding soil or by being driven into contact with rock or a load-bearing soil layer (timber, steel, or precast concrete) o Piers (caissons) – shaft is drilled or dug out and filled with concrete. ? Straight shaft ? Conical footing (bellied pier) • Mat foundation – a thick slab beneath the entire area of a building.A mat may be several feet thick. • Floating foundation – used where soil strength is low…The volume of earth excavated is equal to the weight of the building, minimizing settlement. Underpinning – the process of strengthening an existing foundation. Shoring – refers to temporary supports. May be necessary to support a structure until underpinning can be put into place. Chapter 7: Structural Systems From FF viewpoint, materials & basic structural systems are related. Type I – reinforced concrete or protective steel framing are found Type II – use of unprotected steel can be found Reinforcing Concrete: Ordinary – steel bars are placed in the formwork, and wet concrete is placed in the framework around the bars. o Stirrups – vertical reinforcing steel bars o Vertical & diagonal bars in concrete resist tension • Prestressed – a compressive force is applied by preloading steel bars before a load is applied. Forces are slightly higher than what is actually needed for support. o Pretensioned reinforcing – when the concrete has hardened sufficiently, the force applied to steel strands is released. o Posttensioned reinforcing – steel strands are placed in formwork & covered with grease or in plastic tubing.After the concrete has cured, the strands are then tensioned. Cutting through the steel is dangerous because it is not bonded to the concrete. Concrete Structures: • Cast-in-place – uses slump test to determine moisture content o Flat-slab concrete frame – slab (6-12” thick) is supported by concrete columns ? Drop panels/mushroom capitals – support heavy live loads ? Flat plate system – supports lighter loads & drop panels are not used o Slab & beam – concrete slab supported by concrete beams o Waffle construction Precast Concrete – have more in common with steel-framed buildings than with cast-in-place concrete buildings. Can produce slabs, beams, columns, & wall panels. Does not have continuity of cast-in place type. A corbel is a ledge that projects out from the column & supports the beam. o Solid slab – 30’ spans o Hollow-core o Single & double tee slabs – spans up to 120’ Concrete structural systems can have fire-resistance ratings from 1 to 4 hrs. Structural lightweight concrete has a lower density than ordinary concrete & has lower thermal conductivity. It is a better insulator against heat of fire than ordinary concrete.Steel Framed Structures: • Beam & Girder Frames o Rigid frame – rigidity between beam & column so there is no angle change between the two as loads are applied (Bolted & welded). Vertical members may be rigidly connected to foundation. o Simple frame – primarily designed to support vertical force & some angular change could occur if diagonal bracing were not provided (bolted) o Semi-rigid – not completely rigid but enough to provide diagonal support to structure. When rigid connections are not used, lateral stability for a frame must be provided through the use of diagonal bracing or shear panels. Steel Trusses – can carry loads across greater spans more economically than can steel beams. Used frequently in 3-dimensional space frames. o Open web joist – round bars used for diagonal members are called bar joists o Joist girder – heavy steel trusses used to take the place of steel beams as part of the primary structural frame. • Rigid Frame with inclined roof– Used for spans from 40 to 200’. Top is called the crown & points where the inclined members intersect the vertical members are called the knees. Steel Arches – used to support roofs on buildings where large unobstructed floors are needed (>300’). o Girder arch – solid arch similar to a beam o Trussed arch – uses truss shapes • Steel Suspension systems – steel rods or cables to support roofs providing unobstructed areas w/o reducing vertical clearance at sides of building. • Steel Columns – uses a “slenderness ratio” compares the unbraced length of a column to the shape and area of its cross-section (determines the load that can be safely supported w/o buckling). Square columns & flat stock has fewer tendencies to buckle than tubular type. rotational ends often allow for buckling) Masonry Structures: Traditional masonry structure consists of exterior load-bearing walls that support the floor & roof. These load-bearing buildings can be as tall as 20-stories. Fire rated masonry units can have fire-resistance rating of 2 to 4 hrs. Rule of thumb: bearing wall has header course every 6th course w/ ends of brick facing out. • Nonreinforced walls – stability is from weight of masonry & bonding between adjacent wythes. Usually limited to a max. height of 6-stories o Course – side by side horizontal layer Wythe – horizontal courses laid on top of each other in a vertical layer (supplies strength & stability to a wall) o Stretcher course – bricks placed end to end o Soldier course – bricks placed vertically on end • Reinforced walls – use vertical steel rods & cement grout in center cavity • Lintels – support masonry in V-type pattern…not entire weight of wall • Parapets – prone to collapse • Interior structural framing of masonry buildings – masonry buildings w/ heavy timber interior framing are referred to as mill buildings. o Beam pockets Pilaster – used to increase thickness at the point where a beam transmits a large load to a masonry wall o Fire cut – wood joist/beam slightly angled to allow a beam to fall freely away from a wall w/o acting as a lever against the masonry & do not preclude the collapse of a masonry wall o Masonry walls usually collapse as a result of collapse of the interior framing. Wood Structures: Not economical in buildings over 3-stories • Heavy Timber – columns not less than 8×8”; & beams not less than 6×10”. Similar to steel construction • Post & Beam – posts are 4×4” or 6×6”; posts are spaced 4 to 12’.Less fire hazard do to exposed surface that does not have any combustible voids. • Light Wood Framing – most popular 2”- nominal lumber o Balloon frame – less shrinkage than platform type o Platform frame Chapter 8: Floors & Ceilings: Floor Systems: • Concrete Floors – can be either cast-in-place or precast. It is possible for a concrete floor slab to be supported by either steel beams or trusses. In theses cases, the fire resistance of the floor depends on the fireproofing of the supporting steel. • Tile Arch Floors – this masonry style is not used in modern floor support systems.System uses a tile arch system in combination with steel beams. • Steel Supported Floors o Open web joists – uses lightweight concrete (2” min thickness) supported by corrugated steel decking. The steel decking is supported by web joists. The open web joist can also support precast concrete panels or wood decking. ? Standard span (depth 8 to 30”; spans to 60’) ? Long span ? Deep long span o Steel beam & light gauge steel joints – Steel beams support lightweight cold-rolled floor joists. These joists can be used to support metal deck or wood panel flooring systems.Joist are 6 to 12” in depth & spaced 16 to 48” apart. • Wood Supported Floors – typically have combustible voids. Wood flooring is often covered over by concrete & other materials such as terrazzo and quarry tile. At times no consideration is given to the additional loads imposed on the floor supports. This masonry adds absolutely nothing to the strength of the floor because no steel reinforcement is used. Sudden failure of wood-supported concrete floors has killed many FF. o The most substantial wood floors are found in masonry heavy timber buildings Type IV (floor decking min 3” thick; floor decking is supported by 6×10” beams).Typically no void spaces are permitted. o Bridging – wood/metal diagonal braces or solid blocking is used to distribute concentrated loads between adjacent joists, to increase floor stiffness. o Laminated beams are used in floor support systems. They exhibit a fire behavior similar to that of solid lumber. o Hangers & connectors – take the place of toenailing • Floor coverings – flammability is measured by the level of radiant heat. NFPA uses the critical radiant heat flux test. Higher critical radiant heat flux indicates a lower flammability. o Class I – 0. 43 Btu per ft? er second (lower flammability) o Class II – 0. 19 Btu per ft? per second Ceilings: materials are never rated independently. A ceiling is always rated as part of a floor & ceiling assembly. • Plaster • Gypsum board • Mineral tile • Interstitial space – used in hospitals/laboratories. Allows enough height for walking above a ceiling to facilitate maintenance of equipment. Typically spaces are low in combustibles & automatic sprinklers are not present. Chapter 9: Walls Various types of walls are provided in the design of buildings for purposes other than structural support.Walls constructed for any purpose affect the course of fire in a building. Fire Walls: Erected to limit the maximum spread of fire. It acts as an absolute barrier to a fire under conditions of a total burnout on either side. Not popular with designers due to costs & interference of free movement. Building codes typically allow elimination of fire walls when equipped with automatic sprinklers. Typically constructed of masonry or other fire-resistive materials (concrete block). Usually require a fire resistance rating of 4 hrs. Fire walls must extend beyond walls & roofs to protect exposures (18–36”). • Construction Freestanding – self-supporting & independent of the building frame. Usually found in buildings of wood-frame or masonry construction. Must be able to resist a lateral load of at least 5 pounds per sq ft (NFPA 221) o Tied walls – erected at a column line in a building of steel-frame or concrete-frame construction. • Openings o Doors – must be automatic or self-closing fire doors. If a 4 hr wall is needed then there must be 2 doors with a 3-hr rating on each side. Two doors are required in case one fails to close under fire conditions. o Ducts – if penetrating a fire wall they must be equipped with fire dampers. Special design considerations – in industrial conveyer situations fire walls may need to be penetrated. Solution may be a fire-resistive enclosure around the conveyer in combination with a water spray. Party Walls: a wall that lies on a lot line between two buildings and is common to both buildings. They are almost always load-bearing. Not uncommon for walls to be breached by owners. Fire Partitions: Interior walls used to subdivide a floor or area of a building but do not qualify as fire walls. They are usually erected from one floor to the underside of the floor above.They are frequently used in corridors & occupancy separations. They are also used to create areas of refuge in health care facilities. Fire-resistive partitions create “compartmentalization” of areas. This only provides passive fire-protection. • Construction – material chosen depends on the required fire-resistance & construction type of building. Fire rated glazing can be used for partitions where visibility is needed & a fire rating is required. Enclosure & Shaft Walls: Used to enclose vertical openings, such as stairwells, elevator shafts, & pipe chases, which extend from floor to floor in a building.Required to have a fire-resistance of 1 or 2 hrs. Curtain Walls (cladding): When the main structural frame is the support for a building curtain walls, that only enclose the building, are used. Designed to separate interior from exterior environment. They are used in steel frame & concrete frame structures. Frequently constructed using a combination of glass & steel, stainless steel, or aluminum. They may also be constructed with materials such as lightweight concrete, plastic, fiberglass, and other metal core panels. Because they are not load-bearing, it lacks fire resistance of a more massive load bearing wall.It is not uncommon for buildings to be constructed with curtain walls that are noncombustible but have no fire resistance. Curtain walls are supported at the edge of the floor assembly. Chapter 10: Roofs General points regarding all roofs: • Usually weaker than floors • Many have concealed spaces • Over time, loads may be added to roofs they weren’t designed for • They are subject to wear & deterioration Architectural Styles: • Flat roofs – easiest for FF to work on. Inverted roof is a flat roof with a framework above the main joists to support decking. • Pitched Gable o Hip o Gambrel – slopes in 2-directions with a break in the slope on each side o Butterfly – slopes in 2-directions; 2 shed roofs that meet at lower eaves o Monitor – provides light & ventilation; vertical side normally has glass called a clerestory. o Sawtooth – found on industrial buildings; maximizes natural light & ventilation. o • Curved – most frequently supported by arches & bowstring trusses. A dome roof produces forces similar to those of an arch. That is, horizontal thrusts exist at the base, and compressive forces exist at the top. Lamella arch – constructed from short pieces of wood beveled & bolted together in a diagonal pattern using a special plate (lamella washer). o Geodesic dome – created using spherical triangulation. That is, triangles are arranged in 3-dimensions to form a nearly perfect spherical surface. Roof Supporting System: It is not uncommon for modern roof to deflect or vibrate under the weight of personnel that walk on them…Does not necessarily indicate imminent failure of the roof. • Flat roof • Raftered roof – basic design results in an outward thrust against the buildings walls.Rafters are almost always wood. A ridge beam supports the rafters when an exposed ceiling w/o joists is desired. • Trusses – “monoplane” trusses have all members in the same plane (2×4” or 2×6”; 2-4’ apart). Typical of lightweight trusses. Heavy wood trusses are up to 5-members in thickness & can be spaced 8’ or more apart. • Bowstring • Wood & steel trusses – fink & pratt styles are the most common types used for pitched roofs. • Arches – may be constructed from masonry, concrete, laminated wood, or steel. The behavior of the roof is determined by the material used for the arch.Some arched roofs use a steel tie rod between the two ends of the arch to resist outward thrust. • Rigid frames – can be constructed of concrete, laminated wood, or steel. This type of roof cannot be identified from the outside due to the peaked contour. Inside it can be identified because the frame typically is not concealed. • Rain Roof – a second roof constructed over a damaged/deteriorated original roof Roof Decks: can be constructed of plywood, wood planks, corrugated steel, precast gypsum or concrete planks, poured gypsum, poured concrete (also serves as the supporting members), and cement planks containing wood fiber.Decking made of corrugated steel in combination with concrete is called composite decking. Roof Coverings: The water resistant barrier • Flat roof coverings o Vapor barrier o Thermal insulation o Roofing membrane – actual waterproof material. ? Built-up – tar or asphalt saturated roofing felt (4-layers common) ? Elastomeric-plastomeric membranes – single-layer very thin; attached by adhesives, gravel ballast, mechanical fasteners, or torched. ? Fluid-applied membranes – used on curved roofs in liquid form and permitted to cool in place. o Drainage layer Wear course – protects from mechanical abrasion • Pitched Roof Coverings o Shingles & tiles ? Wood shingles (thin) & shakes (thick) ? Asphalt shingles ? Slate ? Clay tile Fire Ratings of Roof Coverings: NFPA 256, Standard Methods of Fire Tests of Roof Coverings. The number of times a roof covering is tested depends on the material being tested. Classified as: • Class A – effective against severe fire exposure • Class B – effective against moderate fire exposure • Class C – effective against light fire exposure Roof Openings: • Penthouses (bulk-head) – small structures erected on the main roof of a building.Used for elevator machinery, mechanical equipment, or additional living space. • Roof hatches – usually placed over a stairway • Skylights – building codes require wired glass or tempered glass in skylights. Some modern buildings use plastic domes. • Smoke & heat vents – typically found on roofs of industrial & warehouse buildings. Some are designed to open automatically (fusible link) or manually. Plastic domes are designed to soften & fall when exposed to fire. Curtain boards are also used in conjunction with smoke & heat vents. Smoke detection devices are sometimes used to operate vents.Roof vents are not as effective in sprinkled buildings (loss of buoyancy in smoke). Chapter 13: Building Services & Subsystems Some of the most important fire & life safety features built into a structure include compartmentalization & fire resistance. Many services & subsystems penetrate the built-in compartmentalization. Elevators: Have developed into one of the safest & most reliable modes of transportation: ASTME/ANSI A17. 1, Safety Code for Elevators, published by the American Society of Mechanical Engineers. Types are classified by their use: • Passenger • Freight Service elevators – a passenger elevator designed to carry freight Most common power sources electric & hydraulic: • Hydraulic –fluid forced under pressure into a cylinder containing a piston or ram. Hydraulic elevators do NOT have brakes. The piston/ram must be long enough to reach the highest floor (upper limit is usually 6-stories). Most hydraulic elevators have a machine room near the elevator pit. • Electric – either drum or traction devices o Drum – used in older styles where cable is wound the drum. Normally use counter weights to reduce lifting effort of drum.The size of the drum will limit height of building use (still may be found in freight elevators) o Traction – The most common type in buildings over 6-stories high…very fast & has no height limitations. Hoist cables attached to the elevator car run up & over the drive pulley at the top of the hoistway and then down the back wall of the hoistway. The cables do not wind around the drive pulley – they merely pass over it. With the aid of compensating cables, the weight of the elevator car & the counterweights offset each other so the drive motor only has to lift the weight of the passengers.Drive motors can be either AC or DC & have as much as a 500-volt power supply. Traction elevators have a braking system that operates both during normal operation & malfunctions. System uses a brake drum located on the shaft of the drive motor. In a power failure electromagnet releases brake shoes against the drum. ?

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