0. Building Construction Related to the Fire Service
Chapter 3 — The Way Buildings are Built: Structural Design Features

1. Building Construction
Learning Objective 1
Explain the various loads exerted on a building resulting from environmental sources.
Building Construction

2. Building Construction
Load and Gravity
Load – Any effect or force that a structure must resist
Gravity
Force on building through weight of building components and contents
Snow, ice, or water on building adds weight
Total weight of building exerts force on soil beneath it
Building Construction

3. Building Construction
Wind
Basic effects
Direct pressure
Aerodynamic drag
Negative pressure
Secondary effects
Rocking effect
Vibration
Clean-off effect
Building Construction

4. Building Construction
Earthquakes
Slippage between tectonic plates of earth’s surface
Subjects buildings to seismic forces
Occur most frequently in fault zones
Seismic loads far more complex than those for wind
Vibrational motion can be 3-dimensional
(Continued)
Building Construction

5. Building Construction
Earthquakes
Torsional, resonant forces
Force magnitude depends on factors
Most significant force is horizontal motion
Buildings with geometric irregularities more susceptible to earthquake damage
Building codes require stronger seismic bracing for buildings with larger occupancies
(Continued)
Building Construction

6. Building Construction
Earthquakes
(Continued)
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7. Building Construction
Earthquakes
Design methods to protect against forces
Increase stiffness using symmetrical shear walls and cross bracing
Continuous structures with high degree of redundancy in structural frames
Damping mechanisms
Base isolation
Building Construction

8. Building Construction
Soil Pressure
Exerts horizontal pressure against foundation
Can only be estimated
Magnitude depends on several factors
Active or passive
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9. Building Construction
Other Forces
Temperature
Vibration
Shrinkage
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10. Building Construction
Learning Objective 2
Distinguish between the classifications of loads based on origin and movement.
Building Construction

11. Live Loads and Dead Loads
Classification of types of forces resulting from gravity
Dead – Weight of any permanent part of a building
Live – Any load that is not fixed or permanent
(Continued)
Building Construction

12. Live Loads and Dead Loads
Distribution of loads
Uniformly distributed loads
Concentrated load
Snow loads
Water loads
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13. Static and Dynamic Loads
Static – Steady or applied gradually
Dead loads
Many live loads
Dynamic – Involves motion
Wind, earthquakes, vibration, falling objects
Capable of delivering energy in addition to weight
Building Construction

14. Structural Equilibrium and Reactions
Equilibrium – When support provided by structural system is equal to the applied loads
Reactions – Forces that resist the applied loads
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15. Building Construction
Learning Objective 3
Recognize and discuss the internal forces resulting from the loads and forces applied to a structural member.
Building Construction

16. Interior Forces Created by Exterior Loads
Tension – Pull material apart
Compression – Squeeze material
Shear – Slide one plane past an adjacent plane
Strength of materials varies with direction of interior forces
(Continued)
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17. Interior Forces Created by Exterior Loads
(Continued)
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18. Interior Forces Created by Exterior Loads
Stress – Quantity used to evaluate magnitude of interior forces
Factors of safety
Stresses typically occur in combination within a member
Keeping stresses within allowable values determines shape and size of structural members
Building Construction

19. Exterior Loads Classified by Manner Applied
Axial – Applied to center of cross section of structural member and perpendicular to that cross section
Eccentric – Perpendicular to the cross section of the structural member but does not pass through the center of the cross section
(Continued)
Building Construction

20. Exterior Loads Classified by Manner Applied
Torsional – Offset from center of cross section of the structural member and at an angle to or in the same plane as the cross section
Loads change under fire conditions due to thermal energy released
(Continued)
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21. Exterior Loads Classified by Manner Applied
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22. Building Construction
Learning Objective 4
Describe the basic structural components.
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23. Building Construction
Beams
Simply supported
Cantilever
Continuous
Restrained
Primary design consideration – Ability to resist bending from applied loads
Courtesy of Ed Prendergast
(Continued)
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24. Building Construction
Beams
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25. Building Construction
Columns
Designed to support an axial compressive load
Thin columns fail by buckling
Short, squatty columns fail by crushing
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26. Building Construction
Arches
Interior stresses primarily compressive
Produce inclined forces at end supports
Carry loads across a distance
Courtesy of Donny Howard
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27. Building Construction
Cables
Flexible members used to support roofs and brace tents and restrain pneumatic structures
When used to support loads over distance, will assume shape of parabola
Stresses are tension
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28. Building Construction
Trusses
Framed units made up of group of triangles in one plane
If loads applied at only point of intersection of truss members, only compressive or tensile stresses
If has curved top chord, subjected to bending forces
(Continued)
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29. Building Construction
Trusses
Provide inherently rigid frame
Potential for early failure under adverse conditions; failure of any portion of top or bottom chords results in failure of truss
(Continued)
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30. Building Construction
Trusses
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31. Building Construction
Truss Connectors
Wood truss – Pins, bolts, gusset plates, adhesives, brackets, metal straps
Steel trusses – Steel gusset plates, rivets, welds
If connector fails, truss will fail
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32. Building Construction
Truss Connectors
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33. Building Construction
Learning Objective 5
Describe the basic structural systems.
Building Construction

34. Structural Bearing Walls
Span elements such as beams, trusses, and precast concrete slabs
Usually exterior walls with interior support system of columns and beams
Provide lateral support along direction of the wall
Subjected to compressive loads
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35. Frame Structural Systems
Walls enclose frame but provide no structural support
Steel stud wall framing
Post and beam construction
Rigid frames
Truss frames
Slab and column frames
Courtesy of Ed Prendergast
Building Construction

36. Shell and Membrane Systems
Consist primarily of enclosing surface with stresses resulting from applied loads occur within the surface
Courtesy of Ed Prendergast
Building Construction

37. Building Construction
Membrane Structure
Thin stretched flexible material
Addressed in building codes if life of 180 days or more
Addressed in fire codes if life of 180 days or less
Cannot resist compressive forces
Advantages
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38. Building Construction
Shell Structure
Rigid three-dimensional structures having a thickness that is small compared to other structural materials
Regular geometric shapes
Most commonly constructed of concrete
Building Construction