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Forging new generations of engineers

Forging new generations of engineers. STRUCTURAL ENGINEERING. Structure of a Building. The primary function of a building structure is to support and transmit the loads and forces to the ground. “Tracing the Loads” or “Chasing the Loads”. Characteristics of a Structure.

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Forging new generations of engineers

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  1. Forging new generations of engineers

  2. STRUCTURAL ENGINEERING

  3. Structure of a Building • The primary function of a building structure is to support and transmit the loads and forces to the ground. “Tracing the Loads” or “Chasing the Loads”

  4. Characteristics of a Structure • Stability – needed to maintain shape. The structure is dependent upon balanced forces and equilibrium • Strength - ability of the structure to withstand the applied forces, usually includes a “factor of safety” • Economic Value – includes choices made about the design, materials, and function of the structure

  5. Structural Elements • Structural elements in the building consist of: • Stringers or Beams • Girders • Columns • Footings • Connections

  6. Steps in Structural Design • Planning – what function will the structure serve • Preliminary structural configuration and layout • Establishing the loads to be carried • Preliminary sizing of members • Analysis of structural members • Evaluate and compare the preliminary design • Redesign or repeat the above steps as this is an iterative process • Designing and detailing the structural components

  7. Forces and Loads

  8. Design Loads • Dead Loads (DL) – fixed loads • building materials or components and the weight of structural components • Given load of building, which is either calculated or is known • Live Loads (LL) – transient and moving loads • Occupancy loads and furnishing loads, building usage varies • Snow loads • Construction loads • Live Load maybe variable during structures lifetime • Building codes specify Live Loads for floor and roof loadings

  9. Design Loads (continued) WIND • Wind Load (WL) – • Depends on Height and location of structure (Exposure categories) • Resulting loads yields: • Lateral load on walls • Downward and upward pressure on roofs • Overturning of the structure Pressure Uplift Suction

  10. Design Loads (continued) • Earthquake Loads (EQ) • Seismic load based on building mass , type and configuration. • Vertical and lateral forces (dynamic) • Building codes can simplify loading Epicenter Seismic Forces at Base of Building Hypocenter

  11. Design Loads and “Factor of Safety” • Structural Design contains a “factor of safety.” In order to accomplish this, Load Factors are applied to the the various calculated loads. • Building Code requirements are conservative in the methods of distribution and the weights of loads, which adds to the “factor of safety.” • However, to maintain simplicity we will not use any factored loads for the CEA Project.

  12. Loads & Load Paths • Snow and/or roof load • Use and occupancy load • such as DL and LL • Self weight of structure DL • Ground reaction

  13. BEAMS AND COLUMNS

  14. LOADS • The building dead load is the only known load. All other forces will vary in magnitude, duration and location. • The building is designed for design load possibilities that may never occur. • The structural efficiency of a building is measured as the ratio of dead to live load.The building designer strives to keep the ratio low.

  15. Beam Design • Beams are used in floors and roofs. • Maybe called floor joists, stringers, floor beams or girders. • Loads on beams are either concentrated or uniform loads • Beams are designed for Shear, Moment (bending), and Deflection

  16. Beams • Beams are sized appropriately to safely support the loads a structure will carry. • Beams are primarily subjected to bending and shear. • Deflection and deformation can be calculated. • Beams are sized to provide the maximum result with the minimum materials. A factor of safety is included in the design.

  17. Beam Deflection • Limit Deflection to • L/240 of total load (whereas L=length in inches) • L/300 of total load • L/360 of total load (building use throughout life is unknown) Preferred Limit • WHY?? • Ceiling cracks in plaster • Roof ponding (flat roofs) • Visual or psychological reasons, such as too much deflection and people think it could be unsafe • Designer’s judgment

  18. Beam Types • Simple • Continuous • Cantilever Moment (fixed at one end)

  19. Beam Types • Fixed Moments at each end • Propped- Fixed at one end supported at other • Overhang

  20. Columns • Columns carry primary Axial Loads and therefore are designed for compression. • Additional loads from snow, wind or other horizontal forces can cause bending in the columns. • Columns then need to be designed for Axial Load and Bending.

  21. F (External) Column Forces Horizontal loads caused by wind, snow, seismic or internal building load WCOL (External) R1 (Internal) R2 (Internal) WFTG (External) RSoil (External)

  22. LOADS

  23. Weight of the structure (steel, concrete, timber) Partitions/ Walls Ductwork Piping Electrical fixtures Floor coverings Roof coverings Ceiling Building Dead Loads

  24. Typical Building Dead Loads • Concrete (density 150 lb/ft3) per 1 inch thickness 12.5 lb/ft2 • Steel and Timber based on structural element weights • Partitions/ Walls —Wood stud 2x4 12” to 16” on center with ½” gypsum board both sides 6 lb/ft2 — Brick (4” thick) 40lb/ft2 — Concrete Block (8” Wall) 38 lb/ft2

  25. Typical Building Dead Loads • Floor Covering • Tile 12 lb/ft2 • Hardwood 4 lb/ft2 • Linoleum 1 lb/ft2 • Sub floor ¾” plywood 3 lb/ft2 • Ceiling • Suspended 2 lb/ft2 • Drywall5 lb/ft2

  26. Typical Building Dead Loads • Roofing • Sheathing (3/4”) 3 lb/ft2 • Asphalt Shingles 3 lb/ft2 • Insulation Loose ½ lb/ft2 • 3 ply ready roofing 1 lb/ft2 • 5ply felt and gravel 6 lb/ft2 • Mechanical Electrical, Ductwork and Plumbing these loads can vary - Estimated 10 lb/ft2 Estimate depends on the type of building Some may use a percentage of Dead Load

  27. Retail First Floor 100 lb/ft2 Upper Floors 80 lb/ft2 Stadiums and Arenas Bleachers 100 lb/ft2 Fixed Seats 60 lb/ft2 Library Stacks 150 lb/ft2 Reading rooms 60 lb/ft2 Offices50 lb/ft2 Typical Building Uniform Live Loads

  28. Schools Classrooms 40 lb/ft2 First floor corridors 100 lb/ft2 Corridors above first floor 80 lb/ft2 Stadiums and Arenas Bleachers 100 lb/ft2 Fixed Seats 60 lb/ft2 Residential (one and two family) 40 lb/ft2 Hotels and Multifamily Private rooms and corridors 40 lb/ft2 Private rooms and corridors 100 lb/ft2 Typical Building Uniform Live Loads

  29. Snow Load • Snow Load depends on your location. Almost all building codes have Snow Load requirements. • Ground Snow Load ( in New York State) • Rochester, NY 50 lb/ft2 • Albany, NY 55 lb/ft2 • Watertown, NY 65 lb/ft2 • White Plains, NY 45 lb/ft2

  30. Design for Wind Loads • Dead Loads figure in the evaluation of a building when designing for Wind Load. • The building Dead Load can help resist the Overturning and Uplift conditions caused by wind. • Typically, a building framed with steel beams and columns will have some type of bracing, such as steel cross bracing or masonry block walls on exterior or in elevator shaft to handle the wind load conditions. • The floor slab also helps resist wind loads and shear loads

  31. Building Design Steel Frame with Concrete Floors and Flat Roof RETAIL BUILDING

  32. Design notes: • Revit File is for illustrative purposes only. It is a preliminary framing plan and therefore not all steel framing members are accurately noted and resized for final design. • Visibility of Wall, Roof, and Slab can be changed to see total framing plan • Not all walls, slabs, or the roof are shown • Building left in “Under Construction” stage • Steel framed building designed for retail space

  33. Girder Beam Column Footing Partial View of 2nd floor Framing For Clarity the Ground Floor Slab, 2nd Floor Slab and Roof Framing and Roof Deck are not shown

  34. 3D View of Retail Building Steel Framing and 1st Floor Slab Shown

  35. Steps in Calculation • Analysis of structural members, designing for Moment and checking for Deflection • Evaluate and compare to preliminary design • Redesign or Recalculate as necessary, such as repeat the above steps as this is an iterative process • Calculate Beams loading, transfer loads to Girder, and carry the load to the column and then down to the footing

  36. “Load Chasing” for Structural Design The structural design is done by “chasing the loads” of the Dead and Live Load though the slabs, to beams, to girders then onto the columns or walls. The loads are then carried down to the footing or foundation walls and then to the earth below.

  37. Chasing Loads for this project • Calculate Beam loading and obtain reactions • Transfer reaction loads to Girder • Carry the girder reactions to the column and then down to the footing

  38. FOUNDATION PLAN

  39. Design Area Partial 2nd FLOOR FRAMING PLAN

  40. Column B-3 Beam B.3 6’-8” Width Girder 3BC Partial 2nd FLOOR FRAMING PLAN Tributary or Contributing Area for Beam B.3 is shown

  41. Column B-3 Partial Roof FLOOR FRAMING PLAN

  42. Steps for Calculating Beam Loading • Find weights of building elements • Compute weight carried per linear foot of beam and multiple by Tributary Width • Assume weight of beam per lineal foot • Add beam weight to superimposed dead load to get Total Dead Load (DL) • Select Design Live Load (LL) use applicable building codes • Combine DL + LL, this will be the Uniform Load on Beam, w • Calculate any Concentrated Loads on Beam

  43. Steps for Calculating Beam Loading continued • Use MD Solids to set up Beam Loading and generate the Moment, Shear and End Reactions for the beam • Select Member Shape using the Standard Steel Shapes • Define Stress Limits (set Steel Yield Stress Fy=36ksi or 50 ksi) • Compare Beam Design to Allowable Deflection Limits ( L/360) • Select most economical beam ( typically the lightest beam weight) • Deflection may control beam size

  44. Beam and Girder Calculations Second Floor

  45. 2nd Floor Loading for Beam B.3 - Dead Load Span Length 18’-0” Dead Load • 4” thick concrete slab 50 lb/ft2 • Flooring- Ceramic Tile 10 lb/ft2 • Partitions (Drywall with metal stud) 8 lb/ft2 • Suspended Ceiling 2 lb/ft2 • Mechanical/ Electrical Items 10 lb/ft2 Total DL 80lb/ft2 Assumed Dead Load Weight of Beam 20 lb/ft

  46. 2nd Floor Loading for Beam B.3 - Live Load Live Load Retail Space 80 lb/ft2 Total Load DL + LL (per lineal foot of beam) [80lb/ft2 + 80 lb/ft2 ]x6.67 ft = 1067.2 lb/ft Add the Beam Weight of 20 lb/ft Total DL + LL + Beam Weight = 1087.2 lb/ft Use 1090 lb/ft

  47. 2nd Floor Loading for Beam B.3 Uniform Load w= 1090 lb/ft Assume: Simple Beam Loading Condition Span Length is 18 feet. Uniform Load w = 1090 lb/ft

  48. 2nd Floor Beam B.3 - Shear and Moment Shear Moment Max. Moment = 44,145lb-ft Max. Shear = 9,810 lb

  49. Design Results for Beam B.3 Note: Beams were sized using MD Solids By Limiting the Deflection to L /360 Where L = 18ft x 12 in/ft = 216 inches Limit Deflection = L/360 = 216/360 = 0.60 inches

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