Basic structural components are of little value unless they can be assembled into a composite system that will support a building

Construction types and basic structural systems are related

Reinforced concrete or protected steel framing is typical of Type I, fire-resistive buildings

Unprotected steel in a Type I building results in a building being classified as a Type II, noncombustible building

Wood and masonry together are found in ordinary (Type III), heavy-timber (Type IV), and wood frame (Type V) construction

Masonry curtain walls can be found in a building with a steel frame

Unprotected steel beams can be used to support a concrete slab

Possible to use both reinforced concrete and a steel frame, or steel and masonry, for different parts of the building

Structural design involves the blending of the properties of one or more of the construction materials into a unit that will withstand the forces applied to it in a reliable, economical, functional, and attractive manner

• Construction documents that were submitted with the original building permit

Refer to the building department or permit office

• May contain a description of the construction system used

Fire department inspection files

Frequently, all that an inspector can do is to become familiar with prevailing construction methods in the jurisdiction

Bearing wall structures

Loads

Shell and membrane structures

Frame structural systems

Wood structural systems

Masonry structural systems

Steel structural systems

Concrete structural systems

Use the walls of a building to support spanning elements including beams, trusses, and precast concrete slabs

Provide lateral support to the structure along the direction of the wall

Usually exterior walls, but interior walls can provide structural support

Walls are subjected to compressive loads

May be continuous or they may be interrupted for door and window openings

Concrete blocks

Bricks

Stone

Concrete panels

Wood

Dead loads

Live loads

• Fixed in location
• Accurately quantifiable
• Weight of any permanent part of a building, including the weight of the building components
• Dead loads usually remain the same, but they can change

Dead loads

• Any load that is not fixed or permanent like building contents, occupants, snow/rain
• Usually the actual weight and distribution of contents are not known exactly
• Vary by occupancy
• Building codes specify minimum live loads to be used in the design process

Live loads

A concentrated load is one that is applied at one point or over a small area

Produce high localized forces and non-uniform loads in the supporting structural members

Building codes require that a specified minimum concentrated load be used in the structural analysis when it creates greater load effects than the uniform load

Fabric has long been used for tents or other temporary shelters

Newer fabrics can be used as part of the walls and roofs of permanent structures

Consist primarily of an enclosing, waterproof surface

Stresses resulting from the applied loads occur within the surface bearing wall structures

Air-supported structures are supported by the pressurization of the entire surface inside

Membrane structures are permanent; tents are temporary

Building codes typically address membrane structures with a life of 180 days or more

Fire codes address those used for fewer than 180 days

Can usually be erected in less time than a rigid structural system

Fabric can flex and absorb some of the stresses from seismic and wind forces

Fabric also permits the development of innovative architectural shapes

Fabrics weigh less than other roof systems

They must be supported by cables and masts or a tubular framework

The support system must provide sufficient rigidity to avoid shaking or flapping

Fabrics cannot be used to support building appliances

When an automatic sprinkler system is required, the piping must be supported from the framework

Fabrics are considerably thinner than other assemblies used for roof systems; sometimes two layers are used; space between creates a thermal barrier

Must be noncombustible or must meet the fire propagation performance requirements in the locally adopted code

Can also be used in fire-resistive construction when a building code only requires a noncombustible roof for a fire-resistive building

• Walls act as the "skin" to enclose the frame
• Walls may also provide lateral stiffness but provide no structural support

Structural support is provided in a manner similar to the way the skeleton supports the human body

• Frame structural systems are also built using other materials

In the fire service, the term frame construction often refers to a wood-frame building

Relatively closely spaced vertical steel studs connected by top and bottom horizontal members

Historically, has been associated with the use of wood studs

Use of steel studs has become more common in recent years

Frequently provided with diagonal bracing for stability

Both sides may be covered with paneling and sheathing

Posts support the beams that are subject to transverse loads

Evolved from the use of tree trunks for framing

Still commonly associated with wood beams and columns

Other materials can be used

Distinctive characteristic is the spacing of the vertical posts and the cross-sectional dimension of the members

Requires the addition of other members to withstand lateral loads

Can be adapted to a variety of applications

Possible to build components of a frame using a series of trusses

Most frequently encountered in concrete structures

Floor slabs in multistory, reinforced-concrete buildings are supported by concrete columns

Other horizontal systems that can be used to support floor loads include wood decks and metal decks supported by beams and columns

Used when the joints between a column and a beam are reinforced so bending stresses can be transmitted through the joints

Easily recognized in single-story, gabled-roof and rigid-frame buildings

Used in other types of structures including multistory and multispan designs

The joints will be the last portion of the assembly to fail under fire conditions

Interior and exterior framing

One- and two-family dwellings

Townhouses

Apartment buildings

Hotels of five stories or less

Wood framing (Type V)

Post and beam framing

Heavy-timber framing (Type IV)

Walls are formed from vertical members known as studs

Floors are supported by joists or trusses

Inclined roofs are supported by rafters or light trusses

Balloon framing

Platform framing

Will act to retard the spread of fire into the stud spaces

However, if a fire originates in the stud space or spreads into it, it can readily spread from the vertical cavity into the horizontal joists and into the attic space

Fire-stopping must be provided in addition to the structural members

Exterior wall vertical studs are not continuous

First floor is constructed as a platform upon which the exterior vertical studs are erected

Second-story framing is erected on the platform formed by the story joists and flooring

The plate installed on the top of the studs provides a fire-stop that tends to block the spread of fire from floor to floor within the walls

Uses closely spaced members (studs) that are continuous from the sill to the top plate of the roof line

Joists that support the second floor are nailed directly to the studs

Vertical combustible spaces between the studs provide a channel for the rapid communication of fire from floor to floor

Basic structural support is provided by a framework of beams and columns

Exterior walls may be non-load-bearing panels with an exterior siding that may be any of several materials

Ordinary corrugated sheet metal is sometimes used for the exterior walls of small buildings

Interior wood surface is usually left exposed, which eliminates combustible voids and creates a rustic finish

Used to construct bearing walls that provide the basic structural support for a building

Can be used for non-load-bearing curtain walls or partition walls

Exterior walls are used with a variety of framing systems including unprotected steel, protected steel, and wood

Both fire-resistive and non-fire-resistive buildings may feature masonry walls

Masonry units are laid side by side in a horizontal layer known as a course

Horizontal courses of brick are laid on top of each other in a vertical layer known as a wythe

Simplest brick wall consists of a wall with a single wythe

Multiple wythes are commonly used to supply the necessary strength and stability

Stretcher course

• Bricks placed end-to-end

Soldier course

• Bricks placed vertically on end

Header course

• Bricks placed with the end facing out

The weight of the masonry

Horizontal bonding between adjacent wythes

Vertical compressive strength of the masonry units

Corrosion-resistant metal ties provide horizontal bonding

Prevents the seepage of water through the mortar joints

Increases the thermal insulating value of the wall

Placement of metal ties is important because the use of a brick header course usually is not practical

Placing vertical steel rods in a cavity between two adjacent wythes of a brick wall effectively reinforces walls

The cavity is then filled with grout

As the height of a wall is increased, the thickness of the wall at the base must be increased as the load-bearing area of the wall increases

• The increasing weight of a load-bearing wall with increased height makes very tall masonry structures impractical or more costly than alternative designs unless the masonry is reinforced with steel

Disadvantages

• Extending tension rods through the masonry walls; attaching them to thrust plates on the outside
• Thrust plates are usually visible on the outside; may indicate that the building has undergone repairs

Reinforcement method

Can include a combination of unprotected steel, protected steel, and wood

Joists, beams, or trusses are used to transfer the gravity load of the building contents

Masonry buildings with wood interior framing are classified as ordinary (Type III), heavy-timber (Type IV)

Classification depends on the size of the wooden structural members

Depends on the type of masonry units used and the thickness of the wall

As the thickness of a masonry wall increases, generally the fire resistance increases

Building codes usually permit less clearance (separation) between buildings with masonry or other fire-resistive exterior walls

They are less likely to communicate fire from structure to structure

Primary material used for structural support in the construction of large modern buildings

Can be used to construct a frame of columns, beams, and girders

Can be used in heavy or lightweight trusses to support roofs and floors

Rigid frames and arches can be constructed from steel

Steel cables or rods can be used to support roofs

Cold-rolled steel studs are being used to construct exterior walls

Steel is a strong but very dense material

Not efficient to use it in the form of solid slabs or panels

Steel in sheet form, however, is used for applications such as floor decking and exterior curtain walls

Exterior envelope of a steel-frame building can consist of concrete, masonry, or glass

Can be fabricated in a variety of shapes

Frequently used in three-dimensional space frames

Can also be constructed of wood or a combination of steel and wood

Foundation stem walls

Floor slabs

Driveways

Walks

Interior and exterior walls

Roof decks

Floors of upper stories

Stairways

Elevated walkways

Roof tiles

Decorative interior finish

May be precast

May be cast-in-place

May be the construction system for entire structures

Permits the designer to cast the concrete in a wider variety of shapes

Does not develop its design strength until after it has been placed where it will be cured and used

Placed in forms and cured at a precasting plant away from the job site

Transported to the job site and hoisted into position

Buildings can be built using whole precast modular units

Precast parts assembled into a framework for the building are more common

More in common with steel-framed buildings than with cast-in-place concrete buildings

Steel bars are placed in the formwork

Wet concrete is placed in the formwork around the bars

Concrete must be properly compacted as it is placed in the forms to completely surround the rebars

When hardened, it adheres to the reinforcing bars because of textural shaping on the surface of the bars

Needed when a concrete beam or floor slab supports a load

Both processes use the same basic materials

• Uses steel strands stretched between anchors producing a tensile force in the steel
• Concrete is then placed around the steel strands and allowed to harden
• Once hardened, the force applied to the steel strands is released
• Strands exert a compressive force in the concrete

Pretensioned reinforcement

• Uses reinforcing steel that is not tensioned until after the concrete has hardened
• Reinforcing strands are placed in formwork; covered with grease or a plastic tubing to prevent binding
• A jack is used to apply a large tensile force to the steel that stretches the steel and results in a compressive force in the concrete
• Reinforcing cables are trimmed to the edge of the concrete and grouted

Post-tensioned reinforcement

It is difficult to determine which type of reinforcing has been used in a concrete frame building

May also be impossible to distinguish between cast-in-place concrete and precast concrete after a building is completed

In addition, some systems such as stucco and EIFS may appear to be concrete