1. Building Construction
Chapter 13
Building Construction

2. Introduction
Fire departments pride themselves in ability to launch aggressive interior structural attacks
Often, buildings collapse without a “visual” warning
Firefighters must understand how fire travels
Departments need more training on building construction

3. Building Construction Terms and Mechanics
Firefighters need understanding of concepts associated with construction
Intended use of building can add tremendous weight
Elements create building loading
Imposition of loads causes stress called force
Forces delivered to earth for building to be structurally sound

4. Types of Loads Two broad categories:
Dead loads
Live loads
Specific terms for dead loads and live loads:
Concentrated load
Distributed load
Design load
Undesigned load
Fire load

5. Figure The steel stairs and air-conditioning unit apply a concentrated load on this roof structure. Also note the potential instability of the air-conditioning unit placed on cement blocks.

6. Imposition of Loads Loads must be transmitted to structural elements
Terms associated with imposition:
Axial load
Eccentric load
Torsion load

7. Figure There are three types of loads that can be transmitted through a structural member: axial, eccentric, and torsion.

8. Forces Loads imposed on materials create stress
Stress and strain: defined as forces applied to materials:
Compression
Tension
Shear
Several variables determine amount of time a material can resist gravity and fire degradation

9. Figure 13-6 Loads are applied to a structural member as compression, tension, and shear forces.

10. Forces (cont’d.)
Several variables determine amount of time a material can resist gravity and fire degradation
Material type and mass
Surface-to-mass ratio
Overall load being imposed
BTU development
Type of construction (assembly method)

11. Forces (cont’d.) More variables Alterations (undersigned loading)
Age deterioration/care and maintenance of the structure
Firefighting impact loads
Condition of fire-resistive barriers

12. Structural Elements
Buildings are an assembly of structural elements designed to transfer loads to the earth
Can be defined simply as:
Beams
Columns
Walls
Connections

13. Beams Transfers loads perpendicular to its length Types of beams:
Simple beam
Continuous beam
Cantilever beam
Lintel
Girder
Joist
Truss and Purlin

14. Figure A beam transfers a load perpendicular to the load—creating compressive and tensile forces within the beam.

15. Columns
Any structural component that transmits a compressive force parallel through its center
Typically support beams and other columns
Generally vertical supports of building
Can be vertical, horizontal, or diagonal

16. Walls Really long, but slender, column Two categories:
Load-bearing walls
Carries weight of beams, other walls, floors, roofs, other structural elements
Also carries weight of the wall itself
Non-load-bearing walls
Need only support its own weight
Example: partition wall between two stores in a strip mall

17. Connections Weak link as it relates to structural failure during fires
Often small, low-mass material that lacks capacity to absorb heat
Three categories:
Pinned
Rigid
Gravity

18. Fire Effects on Common Building Construction Materials
Many factors determine which material is used to form structural elements:
Cost
Application
Engineering capabilities
Adaptability
Each material reacts to fire in a different way

19. Table 13-1 Performance of Common Building Materials under Stress and Fire

20. Wood Most common building material Relatively inexpensive
Marginal resistance to forces compared to weight
Native wood with more mass takes longer to burn before strength is lost
Engineered wood
Plywood delaminates when exposed to fire
Some composites fail through exposure to heat without burning

21. Steel Mixture of carbon and iron ore
Excellent tensile, shear, and compressive strength
Popular choice for:
Girders
Lintels
Cantilevered beams
Columns
Loses strength as temperatures increase

22. Concrete Mixture of portland cement, sand, gravel, and water
Excellent compressive strength
All concrete contains some moisture
Under heat, moisture expands and causes concrete to crack and spall
Concrete can stay hot long after the fire is out

23. Masonry Common term that refers to brick, concrete block, and stone
Used to form load-bearing walls
Veneer wall supports its own weight
Mortar holds units together and have little or no tensile or shear strength
Excellent fire-resistive qualities

24. Composites Combination of the four basic materials
Includes plastics, glues, and assembly techniques
Example: wooden I beams composed of wood chips and veneers pressed together in I-shape
Structurally stronger but fail quickly when heated
No fire contact required
Steel expands faster than wood, causing stress at intersection between the two materials

25. Figure 13-11 A composite truss
Figure A composite truss. Rapid heating will cause the stamped-steel to separate from the wood chords.

26. Types of Building Construction
Five broad categories of building construction have been developed
Give firefighters basic understanding of:
Arrangement of structural elements
Materials used to construct building
Broad classifications are dangerously incomplete for firefighters
Buildings are built to meet certain codes

27. Type I: Fire Resistive
Elements are of an approved noncombustible or limited combustible material
Typical of Type I:
Monolithic-poured cement
Steel with spray-on fire protection coatings
Typically large multi-storied structures with multiple exit points
Examples: arenas, high-rises, World Trade Center

28. Figure A typical Type I building, with structural members designed to resist the effects of fire for three to four hours. This building is of reinforced concrete construction.

29. Type II: Noncombustible
Not qualified for Type I construction
Are of an approved noncombustible or limited combustible material
Type II buildings are steel
Warehouses
Small arenas
Newer churches
Steel not required to have fire-resistant coating
Susceptible to deformation

30. Figure Buildings of Type II construction will have structural elements with little or no protection from the effects of fire. Remember, in the event of a fire, these unprotected steel structural members may fail and collapse quickly.

31. Type III: Ordinary
Buildings where load-bearing walls are noncombustible
Roof and floor assemblies are wood
Prevalent in most older town “main street” areas
Many void spaces where fire can spread undetected
Common hallways, utilities, attics
Masonry walls hold heat inside, floors and roof beams gravity fit

32. Figure Buildings of Type III, ordinary construction, are common throughout North America. These typical “Downtown USA” buildings provide many challenges to firefighters, such as void spaces and common walls allowing rapid fire extension and little structural protection.

33. Type IV: Heavy Timber
Block or brick exterior load-bearing walls and interior structural members, roofs, floors, and arches of solid or laminated wood without concealed spaces
Buildings are quite stout
Used for warehouses, manufacturing buildings, older churches
New Type IV buildings hard to find
Cost of large-dimension lumber and laminated wood beams makes this building type rare

34. Figure Type IV buildings, heavy timber construction, have large wood structural elements with great mass. The mass of these structural members requires a long burn time for failure. The connections, usually steel, are the weak points in this type of construction.

35. Figure Wood and heavy timber beams were often “fire-cut” so that a fire-damaged, sagging floor would simply slide out of the wall pocket in order to preserve the wall.

36. Type V: Wood Frame Most common construction type
Homes
Newer small businesses
Chain hotels
Balloon frame versus platform framing
Platform framing creates fire stopping
Gypsum board protects wood frame members
Fires that penetrate wall, floor, attic spaces become significant collapse threat

37. Figure The wood frame structure, Type V construction, is the most common type of construction in North America.

38. Other Construction Types (Hybrids)
Methods that do not fit into one of the five types
Combination of more than one type
Other types:
Lightweight steel frame
Insulated concrete formed (ICF)
Structural insulated panel (SIP) wall

39. Figure 13-24 This lightweight steel home is built similar to a Type V
Figure This lightweight steel home is built similar to a Type V. OSB sheeting gives the steel rigidity to torsional loads such as wind.

40. Relationship of Construction Type to Occupancy Use
Many officials and builders first look at anticipated use of building
Occupancy classifications:
Basic arenas
Residential
Commercial
Business
Industrial
Education

41. Collapse Hazards at Structure Fires
Firefighters must understand buildings in their jurisdiction
Reading buildings is essential to anticipate collapse

42. Trusses Truss roof collapses have killed many firefighters
Come in many styles and shapes
Wood trusses commonly used for roof assemblies and floor assemblies
Steel trusses no less susceptible to collapse than wood trusses

43. Figure Wood trusses provide a large surface-to-mass ratio, fuel load, and void spaces—three of the worst structural collapse contributors a firefighter will encounter during structural firefighting operations.

44. Void Spaces Trusses create large void areas
Fires are able to spread horizontally
Fires can start in void spaces because of electrical and utility problems
In Type III ordinary construction, voids are numerous

45. Roof Structures Flat, pitched, or inverted
Many factors determine construction
Roof style may allow a large volume of fire to develop
Some dormers are actually aesthetic and fool ventilation crews

46. Figure 13-30 Some common roof framing styles used in wood frame or ordinary construction.

47. Stairs Believing stairways are durable is a dangerous assumption
Stairs are built offsite and hung in place with metal strapping
Stairs are made with lightweight engineered wood products
Fail quickly when heated

48. Parapet Walls Extension of a wall past top of roof
Used to help hide unsightly roof equipment
Free standing with little stability
Typically collapse when roof starts to sag
Historically, dozens of firefighters have been killed by collapsing parapets

49. Figure This electrical service entrance and attached sign may be the eccentric load causing an early failure of this parapet wall.

50. Collapse Warning Signs
Factors anticipating collapse:
Deterioration of mortar joints and masonry
Overall age and condition of building
Cracks
Signs of building repair
Large open spans
Bulges and bowing of walls
Sagging floors
Large volume of fire
Long firefighting operations

51. Buildings under Construction
Especially unsafe during construction, remodeling, and restoration
Building only meet fire codes when completed
Stacked construction materials may overload other structural components

52. Time No time limits for firefighting operations Truisms have emerged:
The lighter the structural element, the faster it comes down
The heavier the imposed load, the faster it comes down
Wet (cooled) steel buys time
Gravity and time are constant
There is no window of time
Brown or dark smoke from lightweight structures means time is up

53. Preparing for Collapse
Incident commander needs to predict collapse PROACTIVELY
Communicated information between teams help with predicting collapse
Once occupants have been found, fire control should be reduced
Firefighters must not wander into collapse zone

54. Figure 13-35 A minimum collapse zone should be 1½ times the height of the building.

55. Lessons Learned
Many firefighters have been killed as a result of building collapse
Firefighters must understand the buildings in which they fight fires
Knowledge of building construction starts with understanding of loads, forces, and materials
Five class types are being challenged by new construction methods
No rule for how long a building will last on fire