Fire Department: Loads and Forces

• The document is from the Philadelphia Fire Department
• It provides guidance for response to various types of building construction that personnel will encounter
• Manual chapter 201-01 was updated in December 2020

Responsibility

• Each member will exercise control as dictated by rank when implementing this.

Loads and Forces

• Loads include static and dynamic weights from the building itself, or anything placed within or acting upon it
• Dead load is the weight of the building and anything permanently attached.
• Live load is any load applied other than dead loads, typically transient, moving, impacting, or static.

Load Classifications

• Concentrated load: Applied within a small area or at one point.
• Distributed load: Spread over a large surface area or over multiple points.
• Impact load: A moving or sudden load applied in a focused or short time interval (e.g., wind, crowds, fire stream).
• Repeated load: Transient or intermittently applied (e.g., people, escalator).
• Static load: A constant load that rarely moves.
• Suspended load: Hanging from something above.
• Wind/snow load: Atmospheric loads.
• Fire load: Potential heat energy in BTU that may be released when a material burns; a fire service term, not engineering.

Load Imposition

• Load imposition refers to the contact orientation of the load to the materials
• Axial load: Imposed through the center of the material.
• Eccentric load: Imposed off-center, causing material to bend.
• Torsion load: Imposed to cause material to twist.
• Forces: Stresses within a material caused by imposed loads, helping to resist the load.

Primary Forces in Materials

• Compression: Stress that flattens or crushes a material.
• Tension: Stress that pulls apart or stretches a material.
• Shear: Stress that causes a material to tear or slide apart.

Building Material Characteristics

• Material suitability is determined by type, shape, plane orientation, mass, and surface
• Materials are classified as brittle or ductile based on reaction to loads and resistive forces
• Brittle materials fracture or fail when deformed or stressed
• Ductile materials bend, deflect, or stretch under load while retaining some strength

Building Materials

• Traditionally, the four main construction materials were wood, steel, concrete, and masonry
• Material technologies have created composites and hybrid materials with plastics, graphite and wood derivatives

Wood

• Wood has been a basic building construction material for centuries
• Wood is cheap to produce and renewable material for varied building applications
• Moisture content significantly affects wood's strength; structural lumber has 19% or less moisture
• Wood's tensile strength is about 700 psi
• Wood is stronger parallel to the grain

Wood Types

• Dimensional Lumber: Lumber with standard nominal measurements for construction
• Grain: Direction of tree growth.
• Engineered Wood: Bonded wood pieces with glue or resin into shapes.
• Laminated Wood: Wood strips and resin, shaped and bonded with heat or pressure.
• Glue Laminated Beam: Short lumber pieces glued and laminated under pressure for strength.
• Joints: This is the process of joining short pieces of wood during manufacturing

Wood Joints

• Butt Joint: Simple connection of ends, weak joint type.
• Scarf Joint: Overlapping parts secured by glue or fasteners.
• Finger Joint: Interlocking parts secured with glue.

Wood Panels

• Vary greatly from dimensional lumber
• Styles change with technology panels are floor or wall coverings used to encapsulate large areas
• Plywood: Thin veneer layers sliced from logs and glued.
• Oriented Strand Board (OSB): Wood strands glued and compressed.
• Particle Board: Wood particles and synthetic resins, up to 8' by 40' size.
• Sheathing: A layer providing structural stability, insulation, and siding under layer.

Steel

• Steel has been a staple for commercial buildings for two centuries
• Steel beams and trusses have largely replaced wood
• Steel is used for strength, long spans, tall walls, door frames, and nails
• Common forms are I-beam, H-column, and lightweight C-channel
• C-channel replaces wood studs in occupancies with noncombustible or low dead load requirements
• Primary steel alloys are iron and carbon, with less than three tenths of one percent carbon in structural steel
• Late 19th-century steel framing enabled high-rise construction
• Used in fire-resistive and non-fire resistive buildings
• Steel is not inherently fire resistive and fails when exposed to high heat
• Steel is typically protected from fire with insulation

Steel Definitions

• Steel is an alloy of iron and carbon; proportions and elements affect characteristics
• Alloy: Mixture of metals fused to enhance properties
• Cast Iron: Formed from high-carbon pig iron, brittle due to carbon content and lack of alloys
• Rolling: Forming metal into shapes by passing thick bars through rollers
• Unprotected Steel: Steel not protected against heat exposure
• Structure fires can exceed 1,200°F, weakening steel to yield point
• Spray Applied Fire Resistive Material (SRFM): Coating to increase fire resistance, including mineral fiber or aggregates

Concrete

• Concrete is hardened cement from Portland cement, aggregates, and water
• Like masonry it is insect-resistant and non-combustible
• It can be placed in forms for varied architectural shapes
• Concrete is made from low-cost, local materials
• It withstands compression but is weak in tension so must be reinforced
• Compressive strength ranges from 2,500 to 6,00 psi

Concrete Definitions

• Concrete is a hard material from Portland cement, aggregate filler/binder, and water that sets into a rigid building material
• Cement: Adhesive that bonds inert aggregate materials into a solid mass
• Aggregate: Material providing stable bedding or reinforcement
• Admixture: Ingredients added for specific characteristics
• Reinforced Concrete: Fortified with steel reinforcement bars or mesh before hardening
• Reinforcing Bars (Rebar): Steel bars adding strength after concrete sets
• Pre-stressing Stress: Tensioning reinforcing bars before pouring concrete
• Pre-tension Reinforcement Concrete: Steel strands stretched, concrete placed around, and allowed to harden
• Post-tensioned Reinforcement Concrete: Steel strands tensioned after concrete hardens
• Precast Concrete: Building member poured and set in a controlled environment, then shipped to the site
• Cast in Place Concrete: Concrete poured into forms at the building location

Masonry

• Masonry is one of the oldest and simplest building materials
• Techniques evolved into stacking units and bonding them into barriers
• Masonry units lack tensile strength
• Common stones in masonry: Limestone, Sandstone/Brownstone, Granite, Marble, and Slate

Masonry definitions

• Portland Cement: Cement with calcium and aluminum silicate
• When mixed with water, it forms hydraulic cement
• Spalling: Expansion of moisture within masonry makes it break apart
• Wythe: Vertical column of masonry units
• Course: Horizontal layer of masonry units
• Stretcher: Brick laid lengthwise along a wall

Composite Materials and Interior Finishes

• Composite materials combine various materials and assembly methods for maximum strength with minimal mass
• Interior finishes are materials used for exposed walls and ceilings
• Interior finishes may include: Plaster, Gypsum, Wood Paneling, Ceiling tiles, Plastic and Fiberboard.

Plastics

• Plastic is synthetic or semi-synthetic material made of moldable polymers derived from petroleum
• Plastics can be divided into thermoplastics that can be heated and reshaped
• Thermosetting plastics use heat to harden
• Carbon-Fiber reinforced polymer (CFRP): Composite materials that include a reinforcing material bound together with a polymer
• Carbon fiber is strong and carbon content gives steel strength

Structural elements

• Structural elements are essential underpinnings that allow the buildings to stand erect, resist loads, and gravity
• Buildings contain different elements, features, finishes and systems that come together to form an enclosure

Foundations

• Foundation: The building's anchor to earth and base
• Footers/Footings: Weight-distributing pads at the bottom of foundations
• Foundation Walls: Below-grade walls for structural support
• Slabs: Flat horizontal elements resting on the ground
• Pilings: Vertical posts driven into the earth as the foundation or foundation anchor

Vertical Support Members

• Column: Any structural element loaded axially in compression with rectangles, squares, and cylinders being common shapes
• Pillar: A freestanding vertical post, monument, or architectural feature
• Buttress: bracing feature for lateral forces
• Pilaster: Decorative column protruding from a wall

Beams

• Beam: Horizontal structural member subject to compression, tension, and shear
• Simple Beam: Supported by columns at two points near its ends
• Continuous Beam: Supported by three or more columns
• Cantilever Beam: Supported at one end
• Lintel: Beam spans an opening in a load bearing wall
• Girder: Carries other beams
• Ledger: Attached to a wall column as a half shelf
• Joist: Wood or steel beam supports sheathing or decking
• Span is determined by primary supporting members
• Rafter: Sloped wood joist supports roofing coverings between a ridge beam and wall plate
• Ridge Beam: Uppermost beam of a pitched roof; rafters are attached to the ridge beam
• Purlin: Beam placed horizontally and perpendicular to trusses or beams to support roof sheathing or to hang ceilings
• Suspended Beam: Supported from above by cable or rod, also know as a hung beam

Trusses

• Engineered structural element using triangles to distribute loads
• Triangles create open web space, used instead of solid beams
• Consists of triangles formed by straight members connected as nodes

Truss Types

• Planar Truss: Single triangle with a bottom chord and two top chords
• Top chords are in tension, bottom chord in compression
• Parallel Chord Truss: Top and bottom chords run in the same plane
• Can be engineered where the top chord is attached to a support
• Bar Truss: Steel parallel chord truss with angle iron chords and billet web
• Arched Truss: Arched top chord and straight bottom chord, often called bowstring trusses
• Rigid Arch Truss: Curved self-supporting top chord and horizontal bottom chord and members
• Load delivered axially through the bottom chord through the support walls or the columns
• Bowstring Truss: Tied truss with arched upper chord and horizontal tension bottom chord, for compression in the top chord, diagonal web memebers help transfer loads. Diagonal web members help transfer loads and the top chord abuts to the support wall or column.
• Corner Safe Area: When establishing collapse zones apparatus and members should operate from the four corners of the building while still outside of the collapse zone because these areas have the least amount of bricks.

Guidance for responding to various building constructions. Covers types of loads (static, dynamic, dead, live) and load classifications (concentrated, distributed, impact, repeated). Manual updated December 2020.