Footings, Foundations, and Concrete

1. 1 Chapter 11 Footings, Foundations, and Concrete

2. 2 Learning Targets Describe the procedure for staking out a house location. List the major considerations when designing a footing for a residential foundation. Analyze a typical floor plan to determine the appropriate foundation.

3. 3 Learning Targets Discuss the design considerations for wood, concrete, and masonry foundation walls. Calculate the load to be supported by a beam. Explain the purpose of a lintel.

4. 4 Introduction A good foundation is very important. It requires careful planning and design. Types of foundations: Masonry or concrete. All-weather wood. Slab type. Specialized CADD programs are available to aid the process.

5. 5 Types of Foundations Masonry foundation.

6. 6 Types of Foundations All-weather wood foundation.

7. 7 Types of Foundations Slab foundation.

8. 8 Staking Out House Location The plot plan provides the necessary dimensions for staking out the house. The task requires a measuring tape, contractor’s level, and possibly a transit. Locate each corner of the house. Use 9-12-15 unit method for square corners. Check for accuracy by diagonal measurement.

9. 9 Batter Boards Batter boards retain location of the foundation during construction. Locate them 4' outside the footing line. Corner stakes located with a plumb bob. Batter boards are attached to the stakes. Determine a control point (corner). Finished floor should be at least 8" above the grade.

10. 10 Batter Boards Squaring a corner using the 9-12-15 unit method.

11. 11 Checking Accuracy Measuring diagonals.

12. 12 Batter Boards in Place

13. 13 Excavation Top soil should be removed and saved. A backhoe generally used to excavate. Excavation for footings should extend at least 6" into undisturbed earth. The depth of excavation should also be at least 6" below frost penetration. No backfilling under footings. Soil tests determine soil suitability.

14. 14 Excavation Excavation must be large enough to allow space to work on the foundation. Excavation wall should slope away from the bottom of the excavation. Slope angle will depend on soil type. Sandy soil requires a gentle slope. Wall may be nearly vertical in clay.

15. 15 Frost Penetration Chart Average depth of frost penetration in inches.

16. 16 Footing Shapes Footings increase supporting capacity of the foundation wall. Most houses require footings. Soil bearing capacity and weight of house determine the size and type of footing. Footings are generally poured concrete. Footing size is typically based on the foundation wall thickness.

17. 17 Footing Shapes A footing expands load bearing area.

18. 18 Footing Shapes General proportions of a footing.

19. 19 Footing Specifications Footing thickness generally equals the foundation wall thickness. Footing width is twice the wall thickness. Poor soil may require wider footings. Settling occurs during construction. Prevent uneven settling. Check code recommendations. Use steel reinforcing bars.

20. 20 Fireplace and Chimney Footings Fireplace and chimney footings are more massive than regular house footings. Should be reinforced with steel. 12 inches thick. Extend 6 inches beyond the perimeter of the chimney. Cast integrally with house footing.

21. 21 Stepped Footings Stepped footings are necessary when building on hilly terrain. Steps should be placed horizontally. Vertical step height is no more than 3/4 of the distance between the steps. Steps should be multiples of 8 inches in masonry construction. Use 1/2" steel bars in footings.

22. 22 Stepped Footing A stepped footing and foundation wall in masonry construction.

23. 23 Foundation Walls Extend from the first floor to the footing. May also be basement walls. Variety of materials may be used: Cast concrete, concrete block, pressure-treated wood, and stone or brick. Four basic types of foundation walls: T-foundation, slab foundation, pier and post foundation, and wood foundation.

24. 24 Foundation Walls Foundation wall materials.

25. 25 Foundation Walls Foundation types.

26. 26 T-Foundations The T-foundation is the most common type of residential foundation. Name is derived from the shape. Footing and foundation wall are usually separate parts. Footings are usually cast in forms. Variety of applications of T-foundation.

27. 27 T-Foundation Application 8" foundation wall with insulated slab floor.

28. 28 T-Foundation Application 8" basement wall and footing.

29. 29 T-Foundation Application Insulated slab for perimeter heat.

30. 30 T-Foundation Application 12" concrete block foundation for brick veneer on frame.

31. 31 Footing Forms Manufactured forms that stay in place and serve as a drain tile.

32. 32 Slab Foundations A slab foundation is an extension of a slab floor. Cast when the floor is placed. Sometimes called thickened edge slab. Should extend below the frost line. Reinforcement is recommended. Advantages: Requires less time, labor, and expense to construct.

33. 33 Slab Foundation Application Thickened edge slab foundation for frame wall.

34. 34 Slab Foundation Application 8" bearing wall partition on slab floor.

35. 35 Pier and Column Foundations Piers and columns are similar. Pier foundations sometimes replaceT-foundations under the house. Piers often used in a long crawl space. Columns are used in basements where the span is too long. The difference between piers and columns is their height. A column has a footing and post.

36. 36 Pier Foundation

37. 37 Pier Variations

38. 38 Post (Column) Foundation A pipe or adjustable jack post is frequently used to support a beam. This is a column or post foundation.

39. 39 Post (Column) Foundation

40. 40 Wood Foundations Wood foundations are a below-grade, pressure-treated, plywood-sheathed stud wall. Popular where winter weather stops construction. Accepted by HUD, FHA, and FmHA. May be used in basement or crawl space construction.Wood Foundation Typical wood foundation for basement.

41. 41 Concrete and Masonry Basement Walls Factors influencing strength and stability of a basement wall include: Height and thickness. Bond of the mortar in a masonry wall. Vertical loading. Support from cross walls or pilasters. Support from first floor framing. Wall thickness depends on lateral earth pressure and vertical load.

42. 42 Minimum Thickness of Basement Walls

43. 43 Pilasters Pilasters may be used to strengthen basement walls. Built at the same time as the wall. Masonry wall pilasters are usually 8" x 16" in an 8" thick wall. Distance between pilasters should not exceed 15' in an 8" wall and 18' in a 10" wall. Pilasters are also used to support beams.

44. 44 Pilasters

45. 45 Wall Stiffeners Wall stiffeners provide an alternative to pilasters. Accomplished by placing a Number 4 bar in one core of the block from footing to top plate. Another method is horizontal steel joint reinforcement at 16" intervals vertically.

46. 46 Basement Wall Construction Top of wall should be at least 8" above the grade in frame construction. Wood sills should be anchored to basement wall with anchors or clips. Provide at least 7'-5" headroom. Load bearing cross walls in basement are not masonry bonded to entire wall. Use tie bars 1/4" by 1-1/4" by 28" long.

47. 47 Basement Wall Construction A solid cap is recommended to spread the load over the wall. Dampproofing required on the outside of the basement wall: Parge coat and sealer. Excess ground water removal system may be needed.

48. 48 Basement Wall Section

49. 49 Water Removal Method Drain tile placement.

50. 50 Beams and Girders Beams or girders support floor joists over long spans. May be wood or metal. Wood beams may be built-up or solid. Steel beams may be S-beams orW-beams. Size based on weight of the structure and the span.

51. 51 Typical Steel Beams

52. 52 Structure Loads Dead load is the weight of the structure itself: Roofing, siding, joist, etc. Live load is the fixed or moving weights: Furniture, appliances, occupants, snow on the roof, etc.

53. 53 Weight Supported by Beam

54. 54 Load Assumptions First Floor and Second Floor Live + dead load = 50 pounds per square foot. Ceiling Live + dead load = 30 pounds per square foot. Walls Dead load = 10 pounds per square foot. Roof No load on beam.

55. 55 Weight Calculations Example Foundation of the house.

56. 56 Weight Calculations Example Weight of first floor = 56,000 lbs. Weight of second floor = 56,000 lbs. Weight of ceiling = 33,600 lbs. Total weight = 145,600 lbs. Half bears on the beam = 72,800 lbs. First and second floor wall weight total = 6,400 lbs. Weight bearing on the beam = 79,200 lbs.

57. 57 Weight Calculations Example W-beam span and load table.

58. 58 Weight Calculations Example Length of beam = 40 feet. Three columns reduce span to 10'-0" and 19.8 kips(1 kip = 1000 pounds). An 8" x 6 1/2" WF beam will support 23 kips.

59. 59 Weight Calculations Example Three supporting posts are added.

60. 60 Weight Calculations Example Post Selection Size is determined by weight to be supported and length of post. Post must support 26 kips. Post length is 8 feet. Chart (Figure 11-32 in text) shows that a 3" post will support 34 kips.

61. 61 Weight Calculations Example Weight supported by each post.

62. 62 Weight Calculations Example Steep pipe columns load table.

63. 63 Lintels A lintel is a horizontal structural member that supports the load over an opening. Materials Precast concrete, cast-in-place concrete, lintel blocks, steel angle. Bearing surface of steel angle lintel extends into the masonry at least 4".

64. 64 Types of Lintels

65. 65 Precast Lintel In a masonry wall.

66. 66 Steel Angle Lintel In a brick wall.

67. 67 Concrete Concrete is ordered by the cubic yard. One cubic yard is 27 cubic feet. A “six-bag mix” recommended. Concrete is composed of cement, sand, large aggregate, and water. It requires 28 days to fully cure at 70°F.

68. 68 Concrete Finishing A screed used to smooth the surface. A float used to embed large aggregate, remove imperfections, and consolidate mortar. A trowel used to develop a hard, smooth surface.

69. 69 Contraction Joints Contraction joints are used to minimize and control cracking. Place in line with interior columns. Place at changes in width of slab. Maximum spacing of joints is 20 feet.

70. 70 Floor Slabs A concrete floor slab should be placed on 4" to 6" of compacted sand. Slab thickness is 4" minimum. Slabs should not be bonded to footings or columns. A 1" thick sand cushion may be used to separate the slab from the footing.

71. 71 Floor Slab Section

72. 72 Concrete Blocks Used to form exterior and interior walls. Variety of sizes and shapes available. Hollow concrete masonry units. Basic size is 8" x 8" x 16". Actual size is 7-5/8" x 7-5/8" x 15-5/8". Designed for a 3/8" mortar joint. Decorative blocks are available.

73. 73 Common Concrete Blocks

74. 74 Decorative Concrete Blocks