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  • 1. Understanding Residential Timber AS1684 Framed Construction Timber Framing Using AS 1684.2 Span Tables
  • 2. the timber framing standard Currently you should be using the 2006 Edition AS 1684 Residential timber-framed construction
  • 3. the timber framing standard Provides the building industry with procedures that can be used to determine building practice, to • design or check construction details, • determine member sizes, and • bracing and fixing requirements for timber framed construction in non-cyclonic areas (N1 – N4) AS 1684 Residential timber-framed construction
  • 4. AS 1684.2 – CD Span Tables Contains a CD of Span Tables (45 sets in all) for wind zones N1/N2, N3 and N4 for the following timber stress grades: Unseasoned softwood: F5, F7 Seasoned softwood: F5, F7, F8, MGP10, MGP12, MGP15, Unseasoned hardwood: F8, F11, F14, F17 Seasoned hardwood: F14, F17, F27
  • 5. Timber Framed Construction Each set of Span Tables contains 53 separate design tables
  • 6. Timber Framed Construction Using AS 1684 you should be able to design or check virtually every member in a building constructed using timber framing
  • 7. Timber Framed Construction Battens Roofing Rafters Ridge beam Ceiling battens Ceiling Flooring Hanging beams Ceiling battens First floor wall frames Floor joists Ceiling Lintel Wall stud External cladding Wall frame Internal cladding Floor joists Flooring Bearers Stumps or piles
  • 8. AS1684 Scope & Limitations Where can AS1684 be used?
  • 9. AS1684 Limitations - Physical Plan: rectangular, square or “L”-shaped Storeys: single and two storey construction Pitch: 35o max. roof pitch Width: 16m max. (Between the “pitching points” of the roof, ie excluding eaves) 16.0 m max. W W 16.0 m max.
  • 10. Width Pitching Point Pitching Point of main roof. of main roof. Pitching Point Pitching Point of verandah or of garage roof. patio roof. Garage Main house Verandah or Patio 16.0 m max. 16.0 m max. 16.0 m max. The geometric limits of the span tables often will limit these widths.
  • 11. Wall Height The maximum wall height shall be 3000 mm (floor to ceiling) as measured at common external walls, i.e. not gable or skillion ends.
  • 12. Design Forces on Buildings Suction (uplift) Construction loads (people, materials) DEAD LOAD (structure) Internal pressure LIVE LOADS (people, furniture etc.) Wind Suction DEAD LOAD (structure) (a) Gravity loads (b) Wind loads AS1684 can be used to design for Gravity Loads (dead & live) and wind loads.
  • 13. Wind Classification Non-Cyclonic Regions A & B only N1 - W28N 100km/h gust N2 - W33N 120km/h gust N3 - W41N 150km/h gust N4 - W50N 180km/h gust
  • 14. Wind Classification Wind Classification is dependant on : • Building height • Geographic (or wind) region (A for Victoria) • Terrain category (roughness of terrain) • Shielding classification (effect of surrounding objects) • Topographic classification (effect of hills, ridges, etc)
  • 15. Wind Classification - Simple Reference Geographic Region A Site Location Below top 1/3 Top 1/3 of hill of hill or ridge or ridge Suburban site 1. Not within two rows from • The city or town perimeter as estimated 5 years hence N1 N2 • Open areas larger than 250,000m2 2. Less than 250m from • The sea or • open water wider than 250m 3.Within two rows from • The city or town perimeter as estimated 5 years hence N2 N3 • Open areas larger than 250,000m2 Rural areas
  • 16. Using AS1684.2 Span Tables • Design fundamentals & basic terminology • Roof framing • Wall framing Click on • Floor framing arrow to move to section required
  • 17. Design Fundamentals & Basic Terminology
  • 18. Design Fundamentals Battens Roofing NOTE Rafters Ridge beam While you might build from the Ceiling battens Ceiling Bottom – Up Flooring Hanging beams Ceiling battens First floor wall frames You design from the Floor joists Ceiling Lintel Roof – Down Wall stud As loads from aboveExternal cladding can Wall frame Internal cladding impact on members below – so Floor joists start with the roof andFlooring work Bearers down to the ground level or piles Stumps
  • 19. Design Fundamentals Roof • Understanding the concept of a „load path‟ Load is critical. Loads need to be supported down the building to the ground Indirect Load path due to cantilever • As a general rule it is necessary to increase the timber member size when: – Load increases (a function of dead, live, wind loads) Ground level – Span increases (a function of load paths across openings) – Indirect load paths occur (e.g. cantilevers and offsets) • It is possible to decrease timber member size when: – Sharing loads across many members – Using members with higher stress grades
  • 20. Load distribution
  • 21. Loads distributed Loads distributed equally between Points of support. Of the total load on MEMBER X, half (2000mm) will be supported by the beam or wall at A and half (2000mm) will be supported by the beam or wall at B. MEMBER X A B
  • 22. If MEMBER X is supported at 3 or more points, it is assumed that half the load carried by the spans either side of supports will be equally distributed. MEMBER X A B C Beam B will carry 3000mm Beam AC will carry 2000 mm load Beam will carry 1000 mm of (1000 mm plus the 2000 mm on the other side)
  • 23. Span & Spacing
  • 24. Terminology - Span and Spacing Spacing The centre-to-centre distance between structural members, unless otherwise indicated. Joists spacing Joists span (between (centre-line to faces of support mem centre-line) Bearer spacing (centre-line to centre-line) Bearers and Floor joists
  • 25. Terminology - Span and Spacing Span The face-to-face distance between points capable of giving full support to structural members or assemblies. Joists spacing Joists span (between internal (centre-line to faces of support members) centre-line) Bearers and Bearer spacing Floor joists (centre-line to centre-line)
  • 26. Terminology - Single Span The span of a member supported at or near both ends with no immediate supports. Single span This includes the case where members are partially cut through over intermediate supports to remove spring. Saw cut Joint or lap Single span Single span Joint or saw cut over supports
  • 27. Terminology - Continuous Span The term applied to members supported at or near both ends and at one or more intermediate points such that no span is greater than twice another. Continuous Continuous span span NOTE: The design span is the average span unless one span is more than 10% longer than another, in which case the design span is the longest span.
  • 28. Example: Continuous Span 6000mm 1/3 (2000mm) 1/3 (2000mm) 1/3 (2000mm) The centre support must be wholly within the middle third. •Span 1 (2000mm) Span 2 (3925mm) 75mm 75mm 75mm Span 2 is not to be greater than twice Span 1. This span is used to determine the size using the continuous span tables.
  • 29. Terminology – Rafter Span and Overhang n r spa ft e Ra n g e r ha Ov Rafter Rafter spans are measured as the distance between points of support along the length of the rafter and not as the horizontal projection of this distance.
  • 30. Terminology – Wall Construction Loadbearing wall A wall that supports roof or floor loads, or both roof and floor loads. Non-loadbearing walls A non-loadbearing internal wall does not support roof or floor loads but may support ceiling loads and act as a bracing wall. The main consideration for a non-loadbearing internal wall is its stiffness. i.e. resistance to movement from someone leaning on the wall, doors slamming shut etc.
  • 31. Terminology – Roof Construction Coupled roof Ridge board Rafter Ceiling joist otherwise there is nothing to stop the walls from spreading Rafters & Ceiling Joist must be and the roof from collapsing fixed together at the pitching points Ridge board When the rafters are tied Rafter together by ceiling joists so that they cannot spread the Ceiling joist roof is said to be coupled (Collar Tie) This method of roof construction is not covered by AS1684
  • 32. Terminology – Roof Construction Non-coupled roof A pitched roof that is not a coupled roof and includes cathedral roofs and roofs constructed using ridge and intermediate beams. A non-coupled roof relies on ridge and intermediate beams to support the centre of the roof. These ridge and intermediate beams are supported by walls and/or posts at either end. Ridge Beam Rafter Intermediate Beam
  • 33. Return to menu Roof Framing
  • 34. Typical Basic Roof Shapes • The footprint of a building generally consists of a rectangular block or multiple blocks joined together • Roof shapes are made to Skillion cover the footprint while also providing sloping planes able to shed water Gable (Cathedral or flat ceiling) Hip • Common roof shapes Dutch Hip (or Dutch Gable) used to cover the required area are shown above Hip and valley
  • 35. Typical Roof Framing Members Rafter Ridgeboard Collar tie Top plate Top plate Underpurlin Strut Strut Ceiling joist Strutting beam
  • 36. Transferring Loads to Pitched Roofs 3. Rafters – take batten loads and transfers them to the support 2. Battens - take structure below e.g. roofing loads and walls transfers them to the rafters/trusses Support wall 1. Roofing materials - take live/dead/wind loads and transfers them to the battens
  • 37. Batten Design Batten Batten Typical Process Span Spacing Step 1: Determine the wind classification to factor in wind loads – for the example assume noncyclonic winds (N1 or N2) Step 2: Determine type of roof - tiled roof or sheet Step 3: Determine the batten spacing – typically 330mm for tiles, or 450, 600, 900, 1200mm sheet Step 4: Determine the batten span – this will be the supporting rafter spacing
  • 38. Batten Design Batten Span Batten Step 5: Look up Volume 2 of AS1684 (i.e. Spacing non-cyclonic winds N1 & N2) and go to the batten span tables Step 6: Choose a table reflecting your preferred stress grade Step 7: Determine which column in the table to select using the previous “batten spacing” and “batten span” assumptions
  • 39. Roof Batten Design Example Inputs required • Wind Classification = N2 • Timber Stress Grade = F8 • Roof Type = Steel Sheet (20 kg/m2) • Batten Spacing = 900 mm • Batten Span = 900 mm
  • 40. Roof Batten Size 2006 Simplify table Inputs required A 38 x 75mm F8 • Wind Classification = N2 Batten Is adequate • Timber Stress Grade = F8 • Roof Type = Steel Sheet (20 kg/m2) • Batten Spacing = 900 mm • Batten Span = 900 mm
  • 41. Rafter Design Scenario - Rafters for a Ridge beam Cathedral Roof Step 1: Determine the wind classification to factor in wind loads – for the example assume noncyclonic winds (N1 or N2) Step 2: Determine dead/live loads on rafters – for the example assume loads are as for a tiled roof with battens e.g. 60kgs/m2 Step 3: Determine the rafter span – for Rafter the example assume a 2100mm Spacing single rafter span Step 4: Determine the rafter overhang which creates a cantilever span adding extra load – for the example assume a 500mm overhang Step 5: Determine the rafter spacing as this determines how much roof loads are shared between rafters – for the example assume a 600mm spacing
  • 42. Step 6 Look up Volume 2 of AS1684 (N1 & N2) Step 7 Choose a table reflecting your preferred stress grade Step 8 Determine which column in the table to select using the previous “rafter spacing” and “single span” assumptions Step 9 Go down the column until reaching the assumed rafter span and overhang – 2100 and 500mm Step 10 Check the spans work with the assumed roof load of 60kgs/m2 Step 11 Read off the rafter size – 90x45mm
  • 43. Rafter Design Example Inputs required • Wind Classification = N2 • Stress Grade = F8 • Rafter Spacing = 900 mm • Rafter Span = 2200 mm • Single or Continuous Span = Single • Roof Mass (Sheet or Tile) = Steel Sheet (20 kg/m2)
  • 44. Rafter Size 2006 Maximum Rafter or Purlin Span & Overhang (mm) Simplify table Inputs required A 100 x 50mm F8 • Wind Classification = N2 • Stress Grade = F8 rafter • Single or Continuous Span = Single is adequate • Rafter Spacing = 900 mm At least • Rafter Span = 2200 mm 2200mm • Roof Mass (Sheet or Tile) = Steel Sheet (20 kg/m2)
  • 45. Ceiling Joist Design Ridgeboard Rafter Ceiling Joist Design variables • Timber Stress Grade • Ceiling Joist Spacing • Ceiling Joist Span • Single or Continuous Span
  • 46. Ceiling Joist Design Example Inputs required • Wind Classification = N2 • Stress Grade = F17 • Overbatten = No • Single or Continuous Span = Single • Joist Spacing = 450 mm • Ceiling Joist Span = 3600 mm
  • 47. Ceiling Joist Size 2006 Simplify table Inputs required At least • Wind Classification = N2 3600mm • Stress Grade = F17 • Overbatten = No A 120 x 45mm F17 • Single or Continuous Span = Single • Joist Spacing = 450 mm ceiling joist • Ceiling Joist Span = 3600 mm is adequate
  • 48. Ridgeboard OTHER MEMBERS AND COMPONENTS Member Application Minimum size (mm) Depth not less than length of the rafter Unstrutted ridge in coupled roof plumb cut 19 thick Strutted ridge in coupled roof with strut Depth not less than length of the rafter Ridgeboards spacing not greater than 1800 mm plumb cut 19 thick Some members do not have to rafter Depth not less than length of the Strutted ridge in coupled roof with strut spacing greater than 1800 to 2300 mm plumb cut 35 thick be designed using 50 greater in tables Stress grade F11/MGP15 minimum and span depth than rafters 19 thick (seasoned) or 25 thick no lessthey aregrade than rafter stress simply called up or Hip rafters (unseasoned) calculated based onmin. thickness asthan rafters Stress grades less than F11/MGP15 members 50 greater in depth for rafters Minimum stress grade, as for rafters into them framing 50 greater in depth than rafters Valley rafters with thickness as for rafter (min. 35) 19 min. thick width to support valley Valley boards See Note gutter Struts to 1500 mm long for all stress 90 45 or 70 70 Roof struts grades (sheet roof) Struts 1500 to 2400 mm long for all 70 70 stress grades
  • 49. Roof Member - Load Impacts The loads from roof members often impact on the design of members lower down in the structure. This impact can be determined from the following load sharing calculations Roof Load Width (RLW) Ceiling Load Width (CLW) Roof area supported
  • 50. Roof Load Width (RLW)
  • 51. RLW - Roof Load Width RLW is the width of roof that contributes roof load to a supporting member – it is used as an input to Span Tables for • Floor bearers • Wall studs • Lintels • Ridge or intermediate beams • Verandah beams
  • 52. RLW - Roof Load Width 00 00 30 15 1 500 B Roof Load Widths A are measured on the rake of the roof.
  • 53. RLW - Roof Load Width
  • 54. RLW - Roof Load Width x y x y RLW wall A = a RLW wall B = b 2 2 LW RL R W x y a b The roof loads on trusses are distributed equally between walls 'A' and 'B'. A B Trusses
  • 55. RLW - Roof Load Width Without ridge struts x y RLW wall A = a RLW wall B = b 2 2 * For a pitched roof without * * RL ridge struts, it is assumed W RL that some of the load from RLW RL W RL W W the un-supported ridge will travel down the rafter to x y walls 'A' and 'B'. The RLW's a 1 2 b for walls A & B are 3 increased accordingly. A B
  • 56. „RLW‟ - Roof Load Width RL With ridge struts W WR RL LW x y a 1 2 b 3 A C B x Underpurlin 1 = 2 y Underpurlin 2 = 3 y Underpurlin 3 = 3
  • 57. Ceiling Load Width (CLW)
  • 58. CLW - Ceiling Load Width Ceiling load width (CLW) is the width of ceiling that contributes ceiling load to a supporting member (it is usually measured horizontally). CLW x A B
  • 59. CLW - Ceiling Load Width CLW is used as an input to Span Tables for • hanging beams, and • strutting/hanging beams Ridgeboard Hanging beam Ceiling joist Roof strut Hanging Strutting beam beam span 'x' Strutting beam span Underpurlin Hanging Beam Strutting/Hanging Beam
  • 60. CLW - Ceiling Load Width x CLW Hanging beam D = 2 D E CLW CLW x y A B C FIGURE 2.12 CEILING LOAD WIDTH (CLW)
  • 61. CLW - Ceiling Load Width y CLW Strutting/Hanging beam E = 2 D E CLW CLW x y A B C FIGURE 2.12 CEILING LOAD WIDTH (CLW)
  • 62. Roof Area Supported
  • 63. Roof Area Supported EXAMPLE: The STRUTTING BEAM span table requires a ‘Roof Area Supported (m2)’ input. Underpurlin The strutting beam shown A supports a single strut that A/2 B supports an underpurlin. B/2 The „area required‟, is the roof area supported by the strut. This is calculated as follows:- Strut The sum of, half the underpurlin spans either Strutting Beam Strutting Beam Span side of the strut (A/2), multiplied by the sum of half the A B rafter spans either side Roof Area Supported = of the underpurlin (B/2) 2 2
  • 64. Strutting Beam Design Example Inputs required • Wind Classification = N2 • Stress Grade = F8 • Roof Area Supported = 6m2 • Strutting Beam Span = 2900 mm • Single or Continuous Span = Single • Roof Mass (Sheet or Tile) = Steel Sheet (20 kg/m2)
  • 65. F17 Simplify table At least 2900mm Inputs required • Wind Classification = N2 • Stress Grade = F17 • Single or Continuous Span = Single 2 x 140 x 45mm F17 • Roof Mass (Sheet or Tile) = Steel Sheet (20 kg/m2) members are • Roof Area Supported = 6m2 adequate • Strutting Beam Span = 2900 mm
  • 66. Return to menu Top plate Wall Framing
  • 67. Wall Framing Timber or metal bracing Top plate Sheet bracing Common stud Nogging Lintel Wall intersection Bottom plate Jack stud Jamb stud
  • 68. Wall Studs Design Example Inputs required • Wind Classification = N2 • Stress Grade = MGP10 • Notched 20 mm = Yes • Stud Height = 2400 mm • Rafter/Truss Spacing = 900 mm • Roof Load Width (RLW) = 5000 mm • Stud Spacing = 450 mm • Roof Type = Steel Sheet (20 kg/m2)
  • 69. Wall Stud Size 2006 At least 5000mm Simplify table Inputs required • Wind Classification = N2 70 x 35mm • Stress Grade = MGP10 • Notched 20 mm = Yes MGP10 wall studs • Stud Spacing = 450 mm are adequate • Roof Type = Steel Sheet (20 kg/m2) • Rafter/Truss Spacing = 900 mm • Roof Load Width (RLW) = 5000 mm • Stud Height = 2400 mm
  • 70. Top Plate Design Example Inputs required • Wind Classification = N2 • Stress Grade = MGP10 • Rafter/Truss Spacing = 900 mm • Roof Load Width (RLW) = 5000 mm • Stud Spacing = 450 mm • Roof Type = Steel Sheet (20 kg/m2)
  • 71. Top Plate Size 2006 Simplify table At least 5000mm Inputs required • Wind Classification = N2 2 x 35x 70mm • Stress Grade = MGP10 MGP10 top plates • Roof Type = Steel Sheet (20 kg/m2) are adequate • Rafter/Truss Spacing = 900 mm • Tie-Down Spacing = 900 mm • Roof Load Width (RLW) = 5000 mm • Stud Spacing = 450 mm
  • 72. Wall Lintel Design Example Inputs required • Wind Classification = N2 • Stress Grade = F17 • Opening size = 2400 mm • Rafter/Truss Spacing = 900 mm • Roof Load Width (RLW) = 2500 mm • Roof Type = Steel Sheet (20 kg/m2)
  • 73. Lintel Size 2006 Simplify table Inputs required A 140 x 35mm • Wind Classification = N2 F17 Lintel is • Stress Grade = F17 • Roof Type = Steel Sheet (20 kg/m2) adequate • Roof Load Width (RLW) = 2500 mm • Rafter/Truss Spacing = 900 mm Use Use • Opening size = 2400 mm 3000 mm 1200mm
  • 74. Return to menu Floor Framing
  • 75. Floor Members Floor bearers Floor joists
  • 76. Floor Bearers • Bearers are commonly made from hardwood or engineered timber products and are laid over sub-floor supports • Bearers are sized according to span and spacings – typically a 1.8m (up to to 3.6m) grid Be are an rs pa r sp ci are Bearer ng Be Bearer Spacing Span
  • 77. Floor Load Width (FLW)
  • 78. Example „FLW‟ Floor If x = 2000mm Load Width y = 4000mm a = 900mm FLW A = (x/2) +a FLW A = 1900mm FLW B =(x+y)/2 FLW B = 3000mm FLW C =y/2 FLW C = 2000mm
  • 79. Bearer & Floor Joist Design Example Simple rectangular shaped light-weight home Floor joists Bearers 3600 Section • Gable Roof (25o pitch) • Steel Sheet (20 kg/m2) • Wind Speed = N2 4500 • Wall Height = 2400 mm Elevation
  • 80. Bearer Design Example 25o roof load and Floor Joists Bearer A supports both floor load at 450mm crs 1800 3600 Section Floor Load Width (FLW) Bearers at 1800mm crs FLWA = 1800/2 = 900mm
  • 81. Bearer Design Example Roof Load Width (FLW) x y RLW wall A = a 2 W RL RL W x y a b A B RLW = 1986 mm (say 2000 mm) + 496 mm (say 500 mm) Total RLW On Wall A = 2500 mm
  • 82. Bearer Design Example Inputs required • Wind Classification = N2 • Stress Grade = F17 • Floor Load Width (FLW) at A = 900 mm Roof Load Width (RLW) = 2500 mm • Single or Continuous Span = Continuous • Roof Mass (Sheet or Tile) = Steel Sheet (20 kg/m2) • Bearer Span = 1800mm
  • 83. Bearer Size 2006 Simplify table 2 x 90 x 35mm F17 members joined Inputs required together are • Wind Classification = N2 adequate • Stress Grade = F17 • Floor Load Width (FLW) at A = 900 mm Use • Roof Mass (Sheet or Tile) = Steel Sheet 1200mm (20 kg/m2) table Single or Continuous Span = Continuous • Roof Load Width (RLW) = 2500 mm Use • Bearer Span = 1800mm 4500mm
  • 84. Floor Joist Design Example Inputs required • Wind Classification = N2 • Stress Grade = F17 • Roof Load Width (RLW) = 0 mm (just supporting floor loads) • Single or Continuous Span = Continuous (max 1800) • Roof Type = Steel Sheet (20 kg/m2) • Joist Spacing = 450 mm
  • 85. Joist Size 2006 Simplify table 90 x 35mm F17 floor Inputs required joists at 450mm crs • Wind Classification = N2 • Stress Grade = F17 are adequate • Joist Spacing = 450 mm • Roof Type = Steel Sheet (20 kg/m2) • Single or Continuous Span = Continuous (max 1800) At least • Roof Load Width (RLW) = 0 mm 1800mm • Joist span = 1800mm
  • 86. Understanding Residential Timber AS1684 Framed Construction Timber Framing Using AS 1684.2 Span Tables Return to menu