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Class 4 Applying Loads to Buildings

Class 4 Applying Loads to Buildings. Loads to study. Dead loads Live loads Wind loads Flood loads Seismic loads Snow loads Rain loads Extraordinary loads Tributary area concept. Tributary area concept. Area to which the load is applied

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Class 4 Applying Loads to Buildings

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  1. Class 4Applying Loads to Buildings

  2. Loads to study • Dead loads • Live loads • Wind loads • Flood loads • Seismic loads • Snow loads • Rain loads • Extraordinary loads • Tributary area concept Building Design – Fall 2007

  3. Tributary area concept • Area to which the load is applied • Done progressively through building from top to bottom • Required to size specific members • Loads collected until soil support is determined Building Design – Fall 2007

  4. Examples Building Design – Fall 2007

  5. Building Design – Fall 2007

  6. Building Design – Fall 2007

  7. Our First Analysis – Overall Building Stability • Uplift • Sliding • Overturning • We do this to make sure the overall building will be stable before we concern ourselves with the details Building Design – Fall 2007

  8. Uplift • Vertical load path • Does weight of building and elements exceed uplift force (primarily wind)? • Not exceeding does not suggest failure – it suggests that specific connections must be made to hold the element and/or building in place Building Design – Fall 2007

  9. Uplift design process • Dead load(0.6) ≥ Σ uplift forces (vertical) (ASD load combination for wind) • Calculate vertical component of wind since wind is applied normal to the surface Building Design – Fall 2007

  10. Example building Building Design – Fall 2007

  11. Example Building Design – Fall 2007

  12. Building Design – Fall 2007

  13. Need to look at • building/foundation connection • building with foundation attached • Can not take full value of weight per ASCE 7 (see Chap 2) Building Design – Fall 2007

  14. Sliding • Weight of building and friction create the resistance to sliding • Again, can only use 0.6 x dead load (for wind) • Friction occurs between the building and the foundation or the entire building and the soil • Must determine the frictional resistance factor Φ • Frictional resistance = ((tan Φ x N) + passive soil resistance)) Building Design – Fall 2007

  15. Example Building Design – Fall 2007

  16. Again, must take a look at: • Building to foundation connection • Building with foundation attached at the foundation/soil interface Building Design – Fall 2007

  17. Building Design – Fall 2007

  18. Overturning • Apply overturning moments about a pivot point • Resisting moment can only use 0.6 x dead load (for wind) • Overturning forces must be split into horizontal and vertical components and multiplied by appropriate moment arm Building Design – Fall 2007

  19. Example Building Design – Fall 2007

  20. Most likely failure mode is connection of building to foundation • Not likely the entire foundation will overturn Building Design – Fall 2007

  21. Building Design – Fall 2007

  22. Worked example • Work the CCM problem with crawlspace foundation Building Design – Fall 2007

  23. Dead loads • ASCE 7 – Chapter 3 • Commentary Table C3-1 • Must determine building weight 1 of 2 ways • Individual components unit weight x total number of units in building summed or • System unit weight x area of systems summed Building Design – Fall 2007

  24. Dead weight • Review the methods by using the weights from Chap 3 ASCE 7 Building Design – Fall 2007

  25. Examples of material weights Building Design – Fall 2007

  26. Building Design – Fall 2007

  27. Live loads • ASCE Chapter 4 and Table 4-1 • Concentrated loads • Loads on handrails, etc • Live load reduction • Common live loads • MINIMUMS! • Read Chapter C4 in ASCE 7 Building Design – Fall 2007

  28. Table from IBC & Chap 4 ASCE 7 Building Design – Fall 2007

  29. Building code min. loads • Residential – • 1st floor – 40 psf • Bedrooms – 30 psf • Balconies/decks – 60 psf Building Design – Fall 2007

  30. Building Design – Fall 2007

  31. Snow loads – Chap 7 ASCE 7 • Flat roof snow load • Sloped roof snow load Building Design – Fall 2007

  32. Definitions • pg – ground snow load from map • ce – exposure factor • ct – thermal factor • cs – slope factor • γ – snow density pcf Building Design – Fall 2007

  33. ASCE 7 pg map Building Design – Fall 2007

  34. Snow design considerations • Cold roof • Curved roof • Warm roof • Unbalanced snow loads • Snow drifts • Sliding snow • Rain on snow • Ponding on flat roofs • Roof deflections Building Design – Fall 2007

  35. Review ASCE 7 cases • Figure 7-2 • Figure 7-3 • Figure 7-9 • Tables 7-1,2,3,4 Building Design – Fall 2007

  36. Rain loads – Chap 8 ASCE 7 • Only applied when rain can be ‘collected’ • Flat roof – most difficult design situation • Very shallow sloped roof when gutters or drains can back up • γ = 62.4 lb/ft3 Building Design – Fall 2007

  37. Homework 3 • Read Chapters 4, 7, 8 ASCE and associated commentary • Homework 3 on web site – due in one week • Due 9/19/07 Building Design – Fall 2007

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