Ch 02 Concepts of Construction


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  • Ch 02 Concepts of Construction

    1. 1. 2 Concepts of Construction
    2. 2. Objectives (1 of 2) <ul><li>Identify the variety of forces that buildings are subjected to </li></ul><ul><li>Identify the different types of loads and how they are applied to buildings </li></ul>
    3. 3. Objectives (2 of 2) <ul><li>Identify and define key different types of structural members such as columns, beams, and walls </li></ul><ul><li>Identify the variety of different types of structural connections and how they behave in a fire </li></ul>
    4. 4. Introduction <ul><li>How will the buildings in your community react to fire? </li></ul><ul><ul><li>Prefire inspection </li></ul></ul><ul><ul><li>The laws of physics </li></ul></ul><ul><ul><li>Knowledge gained from the field </li></ul></ul>
    5. 5. Gravity <ul><li>Exerts a continued force on a building </li></ul><ul><li>The gravity resistance system </li></ul><ul><li>Unintended loads imposed by fire </li></ul>
    6. 6. Definition of Loads <ul><li>Forces or other actions that result from the weight of all building materials, occupants and their possessions, environmental effects, differential movement, and restrained dimensional changes </li></ul>
    7. 7. Stress and Strain <ul><li>Stress </li></ul><ul><ul><li>Measured in pounds per square inch (psi) </li></ul></ul><ul><ul><li>KIP = 1000 pounds </li></ul></ul><ul><li>Strain </li></ul><ul><ul><li>Actual percent of elongation (deformation) </li></ul></ul>
    8. 8. Three Types of Forces <ul><li>Compression </li></ul><ul><li>Tension </li></ul><ul><li>Torsion </li></ul>
    9. 9. Dead Loads <ul><li>The weight of the building itself and any equipment permanently attached </li></ul><ul><li>Added dead load </li></ul>
    10. 10. Live Loads (1 of 2) <ul><li>Any load other than a dead load </li></ul><ul><ul><li>Assumes even distribution </li></ul></ul><ul><li>Concentrated load </li></ul><ul><ul><li>Accounts for large heavy objects in a building </li></ul></ul><ul><ul><li>Larger than live load requirements </li></ul></ul>
    11. 11. Live Loads (2 of 2) <ul><ul><li>Water trapped on a roof </li></ul></ul><ul><ul><li>Firefighting equipment </li></ul></ul>
    12. 12. Impact Loads <ul><li>Loads delivered quickly </li></ul><ul><ul><li>Lateral impact loads </li></ul></ul>
    13. 13. Static and Repeated Loads <ul><li>Static loads </li></ul><ul><ul><li>Applied slowly and remain constant </li></ul></ul><ul><ul><li>A heavy safe </li></ul></ul><ul><li>Repeated loads </li></ul><ul><ul><li>Applied intermittently </li></ul></ul><ul><ul><li>A rolling bridge crane </li></ul></ul>
    14. 14. Wind Loads (1 of 3) <ul><li>A force applied by the wind </li></ul><ul><ul><li>Small wood buildings are susceptible </li></ul></ul><ul><ul><li>Masonry buildings are less susceptible </li></ul></ul>
    15. 15. Wind Loads (2 of 3) <ul><li>Diaphragm Floors and Bracing </li></ul><ul><ul><li>Designed to stiffen the building against wind </li></ul></ul><ul><ul><li>Diagonal braces </li></ul></ul><ul><ul><li>K-bracing </li></ul></ul>
    16. 16. Wind Loads (3 of 3) <ul><li>Types of Bracing </li></ul><ul><ul><li>Portal bracing </li></ul></ul><ul><ul><li>Masonry walls </li></ul></ul><ul><ul><li>Tube construction  </li></ul></ul><ul><ul><li>Core construction </li></ul></ul>
    17. 17. Concentrated Loads <ul><li>Heavy loads located at one point in a building </li></ul><ul><ul><li>A steel beam resting on a masonry wall </li></ul></ul><ul><li>Piers </li></ul><ul><ul><li>Short columns used to level floors </li></ul></ul><ul><ul><li>Create a gap between the floor and related arch </li></ul></ul>
    18. 18. Axial Load <ul><li>A force that passes through the centroid of the section </li></ul><ul><ul><li>Centroid </li></ul></ul><ul><ul><li>Eccentric load </li></ul></ul>
    19. 19. Fire Loads <ul><li>Represents the potential fuel available to a fire and the total amount of potential energy (heat) in the fuel </li></ul><ul><ul><li>Heat release rate (HRR) </li></ul></ul><ul><ul><li>Q  </li></ul></ul><ul><ul><li>Caloric value </li></ul></ul>
    20. 20. Suspended Loads <ul><li>Suspended from a ceiling or other structure </li></ul><ul><li>Tie rod  </li></ul><ul><li>Suspended high-rise buildings use suspended beams </li></ul>
    21. 21. Safety Factor <ul><li>Represents the ratio of the strength of the material to the safe working stress </li></ul><ul><li>Ultimate strength </li></ul><ul><li>Design load is a fraction of the ultimate strength </li></ul>
    22. 22. Composite Materials <ul><li>Steel and concrete combined </li></ul><ul><ul><li>Can be constructed with bar-joist trusses </li></ul></ul><ul><li>Brick and block-composite wall </li></ul>
    23. 23. Structural Elements <ul><li>Beams, columns, arches, and walls </li></ul><ul><li>Differ on how they support and transfer weight </li></ul><ul><li>Structural frames </li></ul>
    24. 24. Beams <ul><li>Transmits forces perpendicular to the reaction points </li></ul><ul><ul><li>Deflection </li></ul></ul><ul><ul><li>Neutral axis </li></ul></ul><ul><ul><li>Stiffness </li></ul></ul>
    25. 25. Carrying Capacity and Depth of Beams <ul><li>Increases as the square of the depth </li></ul><ul><ul><li>Increases only in direct proportion to increases in width </li></ul></ul>
    26. 26. Types of Beams (1 of 2) <ul><li>Simple </li></ul><ul><li>Continuous </li></ul><ul><li>Fixed </li></ul><ul><li>Overhanging </li></ul><ul><li>Bracket </li></ul><ul><li>Joist, steel joist, and bar joist </li></ul><ul><li>Girder </li></ul>
    27. 27. Types of Beams (2 of 2) <ul><li>Built-up girder </li></ul><ul><li>Spandrel girder </li></ul><ul><li>Lintel </li></ul><ul><li>Grillage </li></ul><ul><li>Cantilever beam </li></ul><ul><li>Suspended beam </li></ul><ul><li>Transfer beam </li></ul>
    28. 28. Beam Loading <ul><li>Distribution of loads along a beam </li></ul><ul><ul><li>May be concentrated in one area </li></ul></ul><ul><ul><li>Create excessive beam loading </li></ul></ul>
    29. 29. Reaction and Bending <ul><li>Reaction </li></ul><ul><ul><li>Result of force exerted by a beam on a support </li></ul></ul><ul><li>Bending moment </li></ul><ul><ul><li>Load that will bend or break the beam </li></ul></ul>
    30. 30. Columns <ul><li>Transmit a compressive force along a straight path </li></ul><ul><ul><li>Struts or rakers </li></ul></ul><ul><ul><li>Bent </li></ul></ul><ul><ul><li>Bay </li></ul></ul><ul><ul><li>Pillar </li></ul></ul>
    31. 31. Decrease in Load-Carrying Capacity <ul><li>Decrease in load-carrying capacity proportionately </li></ul><ul><ul><li>12-foot column vs. 6-foot column </li></ul></ul>
    32. 32. Shapes of Columns <ul><li>Most efficient </li></ul><ul><ul><li>Distributes the material equally around the axis </li></ul></ul><ul><ul><li>As far as possible from the center of the cylinder </li></ul></ul><ul><li>Difficult to attach beams to round columns </li></ul>
    33. 33. Wooden Columns <ul><li>Smoothed off tree trunks </li></ul><ul><li>Almost always hollow </li></ul>
    34. 34. I-Beams vs. H-Beams <ul><li>Steel beams </li></ul><ul><ul><li>I-shaped </li></ul></ul><ul><li>Steel columns </li></ul><ul><ul><li>H-shaped </li></ul></ul><ul><ul><li>Box shaped </li></ul></ul><ul><ul><li>Cylindrical </li></ul></ul>
    35. 35. Types of Columns <ul><li>Piers </li></ul><ul><ul><li>Short, squat columns </li></ul></ul><ul><ul><li>Fail by crushing </li></ul></ul><ul><li>Long, slender columns </li></ul><ul><ul><li>Buckle </li></ul></ul><ul><li>Intermediate columns </li></ul><ul><ul><li>Fail in either manner </li></ul></ul>
    36. 36. Euler’s Law Columns <ul><li>Very long thin columns </li></ul><ul><li>Critical load </li></ul><ul><li>Formula: P c = ( π 2 EI)/L 2 </li></ul>
    37. 37. Temporary Bracing <ul><li>Used in incomplete structures </li></ul><ul><li>Also known as guy bracing </li></ul>
    38. 38. Walls (1 of 3) <ul><li>Transmit the compressive forces applied along the top or received at any point </li></ul><ul><li>Main divisions of walls: </li></ul><ul><ul><li>Load-bearing </li></ul></ul><ul><ul><li>Non-load-bearing </li></ul></ul><ul><ul><li>Cross </li></ul></ul>
    39. 39. Walls (2 of 3) <ul><li>Veneer </li></ul><ul><li>Composite </li></ul><ul><li>Header </li></ul><ul><li>Stretcher </li></ul><ul><li>Panel </li></ul><ul><li>Curtain </li></ul><ul><li>Party </li></ul>
    40. 40. Walls (3 of 3) <ul><li>Fire </li></ul><ul><li>Partition </li></ul><ul><li>Demising </li></ul><ul><li>Rubble masonry </li></ul><ul><li>Wythe  </li></ul>
    41. 41. Cantilever Walls <ul><li>Severe winds </li></ul><ul><ul><li>May topple a free-standing wall </li></ul></ul><ul><ul><li>Eccentric loading </li></ul></ul><ul><ul><li>Precast concrete tilt slab walls </li></ul></ul>
    42. 42. Wall Bracing <ul><li>Serpentine </li></ul><ul><li>Buttresses </li></ul><ul><li>Pilasters </li></ul><ul><li>Wall columns </li></ul><ul><li>Cavity or hollow </li></ul>
    43. 43. Wall Breaching <ul><li>Homogenous walls </li></ul><ul><ul><li>Act as one unit </li></ul></ul><ul><li>Obstructed load </li></ul><ul><ul><li>Window or door </li></ul></ul><ul><ul><li>Does not follow a vertical path </li></ul></ul>
    44. 44. Roofs <ul><li>Vital to the stability of the structure </li></ul><ul><li>Roof damage </li></ul><ul><ul><li>Can cause wall collapse </li></ul></ul>
    45. 45. Arches <ul><li>Combine the function of the beam and column </li></ul><ul><li>Tend to push outward at the base </li></ul><ul><li>Voussoir </li></ul>
    46. 46. Rigid Frames <ul><li>Derived from the arch </li></ul><ul><li>Steel rigid frames </li></ul><ul><ul><li>Industrial and commercial buildings </li></ul></ul><ul><li>Wooden rigid frames </li></ul><ul><ul><li>Churches </li></ul></ul>
    47. 47. Shells and Domes <ul><li>Shell </li></ul><ul><ul><li>Thin, curved plate </li></ul></ul><ul><ul><li>Concrete </li></ul></ul><ul><li>Dome </li></ul><ul><ul><li>A shell and three dimensional arch </li></ul></ul><ul><ul><li>Geodesic domes </li></ul></ul>
    48. 48. Transmission of Loads <ul><li>Transmission </li></ul><ul><ul><li>Spread from the point of application to the ground </li></ul></ul><ul><ul><li>Must be continuous </li></ul></ul><ul><ul><li>Any failure will lead to collapse </li></ul></ul><ul><ul><li>Accurate knowledge of the ground </li></ul></ul>
    49. 49. Foundations <ul><li>Delivers loads to the ground </li></ul><ul><li>Foundation materials differ </li></ul><ul><ul><li>Almost all are concrete </li></ul></ul>
    50. 50. Connections (1 of 3) <ul><li>Transfer the load from one structural element to another </li></ul><ul><li>Only as strong as its weakest link </li></ul>
    51. 51. Connections (2 of 3) <ul><li>Pinned </li></ul><ul><ul><li>Elements are connected by simple connectors such as bolts, rivets, or welded joints </li></ul></ul><ul><li>Rigid-framed building </li></ul><ul><ul><li>Connections are strong enough to reroute forces if a member is removed </li></ul></ul>
    52. 52. Connections (3 of 3) <ul><li>Monolithic concrete  </li></ul><ul><li>Wet joint  </li></ul><ul><li>Plastic design  </li></ul>
    53. 53. Failure of Connections (1 of 2) <ul><li>Masonry walls shift outward </li></ul><ul><li>Temporary field bolting of steel </li></ul><ul><li>Ledger board  </li></ul><ul><li>Steel connectors rust </li></ul><ul><li>Concrete disintegrates </li></ul><ul><li>Sand-lime mortar is water soluble. </li></ul>
    54. 54. Failure of Connections (2 of 2) <ul><li>Gravity connections </li></ul><ul><li>Gusset plates </li></ul><ul><li>Gang nails </li></ul>
    55. 55. Overhanging and Drop-in Beams <ul><li>Economical </li></ul><ul><li>No support from below </li></ul>
    56. 56. Spliced Beams <ul><li>If beam not long enough </li></ul><ul><ul><li>Spliced with connectors </li></ul></ul><ul><ul><li>Connectors fail in heat </li></ul></ul>
    57. 57. Summary <ul><li>Gravity </li></ul><ul><li>Gravity resistance system </li></ul><ul><li>Specific terms </li></ul><ul><li>Structural elements </li></ul><ul><li>Composite material </li></ul><ul><li>Connections </li></ul>