Lesson 3 Floor screeds _suspended floors.pptx

construction

1. Construction Technology III Lesson 3 By Esther Njoki

2. Timber Suspended Upper Floors

3. Timber Suspended Upper Floors A timber suspended upper floor consists of a series of beams or joists supported by load bearing walls sized and spaced to carry all the dead and imposed loads. Joists are normally spaced at 400mm c/c

4. Timber Suspended Upper Floors support and restraint

5. Joists built into load bearing wall

6. Joists supported on galvanized steel joist hangers

7. Joists strapped to external wall with galvanized steel L straps Restraint strap

8. Joists strapped to external wall with galvanized steel L straps – cont’d L straps to tie in at least 3 joists with bridging between joists under straps

9. Strutting As the span of the joists increases above 3m, there is a tendency for the joists to twist which could cause damage to the ceiling below To prevent this twisting, strutting is usually included if the span of the floor exceeds 2.5m There are two forms of strutting: Herringbone strutting Solid strutting

10. Herringbone Strutting

11. Herringbone Strutting – cont’d

12. Herringbone Strutting – cont’d

13. Herringbone Strutting – cont’d

14. Solid Strutting – cont’d

15. Solid Strutting – cont’d

16. Solid Strutting – cont’d

17. Solid Strutting – cont’d

18. Openings in upper floors

19. Openings in upper floors – cont’d Trimming members are incorporated in upper floors to allow for openings such as stairwells and chimneys. Trimming members are edge members of an opening in a floor and are the same depth as common joists but are usually 25 mm wider since they bare more load.

20. Openings in upper floors – cont’d

21. Trimming Members – cont’d

22. Joints used for trimming members

23. Joints used for trimming members

24. Joints used for trimming members Tusk tenon joint

25. Joints used for trimming members

26. In-situ RC suspended floor A simple reinforced concrete flat slab cast to act as a suspended floor is not usually economical for spans over 5 m. To overcome this problem beams can be incorporated into the design to span in one or two directions. Beams usually span between columns which transfers their loads to the foundations .

27. In-situ RC suspended floor – cont’d Simple reinforced concrete flat slab

28. In-situ RC suspended floor One way slab

29. In-situ RC suspended floor cont’d Two-way slab

30. In-situ RC suspended floor – cont’d

31. In-situ RC suspended floor – cont’d The disadvantages of introducing beams are: The greater overall depth of the floor construction Increased complexity of the formwork and reinforcement To reduce the overall depth flat slabs can be used where the beam is incorporated with the depth of the slab. This method usually results in a deeper slab with complex reinforcement especially at the column positions.

32. In-situ RC suspended floor – cont’d Hidden beams

33. In-situ RC suspended floor – cont’d

34. In-situ RC suspended floor RIBBED FLOORS Used to reduce the overall depth of a traditional cast in-situ reinforced concrete beam and slab suspended floor The wide spaced deep beams are replaced with narrow spaced shallow beams or ribs which will carry only a small amount of slab loading. Can be designed as one or two way spanning floors

35. In-situ RC suspended floor RIBBED FLOORS – cont’d One way spanning ribbed floors are also called troughed floors.

36. In-situ RC suspended floor RIBBED FLOORS – cont’d Formwork for ribbed floor

37. In-situ RC suspended floor RIBBED FLOORS – cont’d Two way spanning ribbed floors are also called coffered or waffle floors.

38. In-situ RC suspended floor RIBBED FLOORS – cont’d Coffered or waffle floors

39. In-situ RC suspended floor RIBBED FLOORS – cont’d Advantages of ribbed floors include: Greater span and load potential per unit weight than flat slab construction. Reduction in dead load The regular pattern of voids created with waffle moulds produces a honeycombed effect, which may be left exposed in utility buildings such as car parks. Creating a continuous void for accommodation of service cables and pipes .

40. In-situ RC suspended floor RIBBED FLOORS – cont’d Ribbed floors are usually cast against metal, glassfibre or polypropylene preformed moulds which are temporarily supported on plywood decking, joists and props

41. In-situ RC suspended floor RIBBED FLOORS – cont’d Preformed moulds for waffle floors

42. In-situ RC suspended floor RIBBED FLOORS – cont’d

43. In-situ RC suspended floor HOLLOW POT FLOORS These are ribbed floors with permanent formwork in the form of hollow clay or concrete pots. Their main advantage is that it has a flat soffit which is suitable for the direct application of a plaster finish or an attached dry lining . The voids in the pots can be utilized to house small diameter services within the overall depth of the slab. These floors can be designed as one or two way spanning slabs , the common format being the one way spanning floor.

44. In-situ RC suspended floor HOLLOW POT FLOORS – cont’d

45. In-situ RC suspended floor HOLLOW POT FLOORS – cont’d

46. In-situ RC suspended floor HOLLOW POT FLOORS – cont’d

47. Provide an alternative form of floor construction to suspended timber floors and in-situ reinforced concrete suspended floors. Precast concrete floor

48. Advantages of precast concrete floors include: Elimination of the need for formwork Curing time of concrete is eliminated, therefore the floor is available for use as a working platform at an earlier stage. Superior quality control of product is possible with factory produced components. Precast concrete floor – cont’d

49. Disadvantages of precast concrete floors include: Less flexible in design terms Formation of large openings in the floor for ducts, shafts and stairwells usually have to be formed by casting an in-situ reinforced concrete floor strip around the opening position. Higher degree of site accuracy is required to ensure that the precast concrete floor units can be accommodated without any alterations or making good . Precast concrete floor – cont’d

50. Precast concrete floor – cont’d Solid Aerated Concrete Floor

51. Precast concrete floor – cont’d Solid Aerated Concrete Floor

52. Precast concrete floor – cont’d Hollow block sections floor

53. Precast concrete floor – cont’d PCC beam and pot composite floor

54. Precast concrete floor – cont’d PCC beam and pot composite floor

55. Precast concrete floor – cont’d PCC plank and pot composite floor

56. Precast concrete floor – cont’d PCC plank and pot composite floor

57. Precast concrete floor – cont’d PCC plank and pot composite floor

58. Precast concrete floor – cont’d PCC cored units

59. Precast concrete floor – cont’d PCC cored units

60. Precast concrete floor – cont’d . PCC channel units

61. Precast concrete floor – cont’d . PCC channel units

62. Precast concrete floor – cont’d . Bearing considerations

63. Precast concrete floor – cont’d . Bearing considerations

64. Precast concrete floor – cont’d . Bearing considerations Steel supports

65. Precast concrete floor – cont’d . Bearing considerations

66. Steel fabricated beams can be used as an integral means of support for precast concrete floors. These are an overall depth and space-saving alternative compared to down-stand reinforced concrete beams or masonry walls. Only the lower steel flange of the steel beam is exposed . To attain sufficient strength, a supplementary steel plate is welded to the bottom flange of standard UC sections Precast concrete floor – cont’d . Fabricated beam

67. Precast concrete floor – cont’d . Fabricated beam

68. Precast concrete floor – cont’d . Fabricated beam

69. Precast concrete floor – cont’d . Asymmetric beam A standard manufactured steel beam with similar applications to the plated UC Used with lightweight flooring units , such as precast concrete hollow core slabs

70. Precast concrete floor – cont’d . Asymmetric beam

71. Precast concrete floor – cont’d . Asymmetric beam

72. Precast concrete floor – cont’d . Opening considerations

73. Floor screeds

74. A floor screed is usually a cementitious material made from a 1:3 or 1:4 ratio of cement to sand . It may be applied onto either a solid in-situ concrete ground floor slab or onto a precast concrete floor unit. Screeds are required when a colourful or functional floor is needed rather than a bare concrete surface. Floor screeds

75. To give a smooth and level floor surface. Screeding fills in gaps and removes high spots on the concrete floor slab. Enables floors to be laid to falls , in other words a slight slope, to assist with drainage. Used to give a concrete floor a finish suitable to receive the floor finish such as coverings carpet, tiles, natural stone, linoleum, wood flooring, resin coatings etc. A screed is preferred when laying underfloor heating . Functions of floor screeds

76. Floor screeds should not be laid in bays since this can cause curling at the edges. Curling is the distortion of a slab into a curved shape by upward or downward bending of the edges. Levelling of screeds is achieved by working to levelled timber screeding batten or square steel bar or alternatively a 75 mm wide band of levelled screed with square edges can be laid to the perimeter of the floor prior to the general screed-laying operation. Laying floor screeds

77. Laying floor screeds – cont’d

78. Evaluate the surface of the base Estimate materials used for screeding Prepare the base Prepare the floor screed mixture Apply bonding agents such as water or bonding slurry Place the floor screed mixture, compact and level Float your screed to remove some imperfections from the new screed floor layer Finally, properly cure the placed materials Procedure of Floor Screeding

79. Procedure of Floor Screeding

80. Bonded screed Monolithic screed Separate screed Unbonded screed Floating screed Types of floor screeds

81. The screed is connected directly to the substrate so that it is effectively bonded to the substrate. Screed is laid onto a mechanically prepared substrate with the intention of maximizing potential bond. Screed is usually laid directly onto the concrete floor If screed is laid directly onto a cured concrete substrate, without any method of bonding, it is classified as semi bonded screed . If a bonding agent is applied prior to screeding, the screed is considered as bonded. Alternatively, screed can be laid directly on concrete floor slab within three hours of placing concrete Bonded Screed

82. Bonded Screed – cont’d

83. This refers to screed intentionally separated from the substrate by the use of a membrane Unbonded screeds are not bonded directly to the base , but laid directly over a polythene/ Damp Proof Membrane (DPM) laid on top of the concrete base or a DPM and insulation. The screed thickness should not be less than 50mm to reduce risk of cracking and curling. The separating layer is introduced beneath the screed to enable independent movement of the flooring system in relation to the base. Unbonded Screed

84. Unbonded Screed – cont’d

85. Unbonded Screed– cont’d

86. Floating screeds are unbonded screeds but generally laid on a layer of rigid insulation material. This application is suitable for use with cast-in water pipes to provide underfloor heating. In this case the screed is known as heated floor screed. They are mainly used for situations where acoustic or thermal insulation is needed. It requires a thickness of 50 – 65mm , even up to 75mm for heavily-loaded floors. Floating Screed

87. Floating Screed – cont’d

88. A resilient quilt of 25 mm thickness may also be laid with butt joints and turned up at the edges against the abutment walls, the screed being laid directly over the resilient quilt. The main objective of this form of floor screed is to improve the sound insulation properties of the floor. Floating Screed – cont’d Resilient quilt

89. Floating Screed – cont’d