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AS 1684 Teaching Guide TIMBER FRAMING USING AS 1684.2 SPAN TABLES AS AS1684-2010 1684-2010 Residential Residentialtimber-framed timber-framedconstruction construction • Go to www.education.WoodSolutions.com.au for up to date teaching resources including an annotated copy of the standard. • This powerpoint presentation is part of a series that has been revised to reflect the requirements of AS 1684 Parts 2 & 3 – 2010 Edition. • Some major changes to this edition include amendments to wall nogging requirements, inclusion of ring beam systems and an Appendix of building practices for engineered wood products (EWPs). • The MGP span tables provided with the Standard have also been amended. AS 1684 theTIMBER-FRAMED timber framing standard RESIDENTIAL CONSTRUCTION Currently you should be using the 2010 Edition. AS 1684 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 AS 1684.2 – CD TIMBER-FRAMING STANDARD Span Tables Contains a CD of Span Tables (45 sets in all) for wind zones N1 - 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 AS 1684 TIMBER-FRAMING STANDARD Each set of Span Tables contains 53 separate design tables AS 1684 TIMBER-FRAMING STANDARD Using AS 1684 you should be able to design or check virtually every member in a building constructed using timber framing. AS 1684 TIMBER-FRAMED CONSTRUCTION Ridge beam Battens Rafters Hanging beams Ceiling Ceiling battens First floor wall frames Roofing External cladding Floor joists Flooring Ceiling battens Wall frame Wall stud Floor joists Stumps or piles Lintel Internal cladding Flooring Bearers AS 1684 Scope and Limitations WHERE CAN AS1684 BE USED? AS 1684 Physical Limitations - W 16.0 m max. 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, i.e. excluding eaves) W 16.0 m max. AS 1684 Width Physical Limitations - Width The geometric limits of the span tables often will limit these widths. Pitching Point of main roof. Pitching Point of main roof. Pitching Point of verandah or patio roof. Pitching Point of garage roof. Garage 16.0 m max. Main house 16.0 m max. Verandah or Patio 16.0 m max. AS 1684 Wall Height Physical Limitations – 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). AS 1684 Design Forces on Buildings Physical Limitations – Design Forces on Buildings AS1684 can be used to design for Gravity Loads (dead & live) and wind loads. Suction (uplift) Construction loads (people, materials) DEAD LOAD (structure) LIVE LOADS (people, furniture etc.) Wind Internal pressure Suction DEAD LOAD (structure) (a) Gravity loads (b) Wind loads AS 1684 Wind Classification 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 AS 1684 Wind Classification Wind Classification Wind Classification is dependent 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.) AS 1684 Wind Classification – Simple References Geographic Region A Site Location Suburban site Not within two rows of: • City or Town perimeter (as estimated 5 years hence) • Open areas larger than 250,000 m2 Top ⅓ of hill or ridge Below top ⅓ of hill or ridge N2 N1 N3 N2 Less than 250m from: • the sea • open water wider than 250m Within two rows of: • City or Town perimeter (as estimated 5 years hence) • Open areas larger than 250,000 m2 Rural areas AS 1684 Using Span Tables Design fundamentals & basic terminology Roof framing Wall framing Floor framing (Click on arrow to move to section required) AS 1684 Using Span Tables DESIGN FUNDAMENTALS & BASIC TERMINOLOGY AS 1684 SPAN TABLES Design Fundamentals – Load Path Design Fundamentals You build from the Bottom up. But you design from the Roof down because loads from above can impact on members below. So start with the roof and work down to the ground level. AS 1684 SPAN TABLES Design Fundamentals – Load Path Understanding the concept of a ‘load path’ is critical. Loads need to be supported down the building to the ground. Roof Load Indirect Load path due to cantilever Ground level AS 1684 SPAN TABLES Design Fundamentals – Load Path As a general rule it is necessary to increase the timber member size when: Load increases (a function of dead, live, wind loads). 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. Roof Load Indirect Load path due to cantilever Ground level AS 1684 SPAN TABLES Loads distributed Design Fundamentals – Load Distribution Loads are distributed equally between Points of Support. MEMBER X A B Of the total load on Member X one half (2000 mm) will be supported by the beam or wall at “A” and the other half (2000 mm) will be supported by the beam or wall at “B”. AS 1684 SPAN TABLES Design Fundamentals – Load Distribution If Member X is supported at three or more points it is assumed that half the load carried by the spans either side of supports will be distributed equally. MEMBER X AA BB Beam A will carry 1000 mm of load Beam B will carry 3000 mm (1000 mm plus 2000 mm on other side) Beam C will carry 2000 mm CC AS 1684 SPANTerminology TABLES - Span and Spacing Terminology – Span Span is the “face-to-face” distance between points capable of giving full support to structural members or assemblies. Joist Span (between internal faces of these support members). Bearers and Floor Joists AS 1684 SPAN TABLES Terminology – Single Span The span of a member supported at or near both ends with no immediate supports. Si ngl e 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 AS 1684 SPAN TABLES 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 span Continuous 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. AS 1684 SPAN TABLES Example: Continuous Span Continuous Span Example 6000 mm 1/3 (2000 mm) 1/3 (2000 mm) 1/3 (2000 mm) The center support must be wholly within the middle third. Span 1 (2000 mm) 75 mm Span 2 (3925 mm) 75 mm 75 mm Span 2 is not to be greater than twice Span 1. This span is used to determine the size using the Continuous Span tables. AS 1684 SPAN TABLES Terminology – Rafter Span and Overhang Terminology - Rafter Span and Overhang 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. pa s er t f Ra Ov e n r ha n g Rafter AS 1684 SPANTerminology TABLES - Span and Spacing Design Fundamentals – Spacing Spacing is the centre-to-centre distance between structural members unless indicated otherwise. Joist Spacing (Centreline-to-Centreline) Bearers and Floor joists Bearer Spacing (Centreline-to-Centreline). AS 1684 SPAN TABLES Terminology – Wall Construction Terminology – Wall Construction Loadbearing wall A wall that supports roof loads, floor loads or both. Non-Loadbearing internal wall A wall that 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.). AS 1684 SPAN TABLES Terminology – Roof Construction Terminology – Roof Construction Coupled Roof - rafters are tied together by ceiling joists so that they cannot spread. Ridge board Rafter Ceiling joist Rafters & Ceiling Joist must be fixed together at the pitching points Ridge board Rafter Ceiling joist (Collar Tie) This method of roof construction is not covered by AS1684 otherwise there is nothing to stop the walls from spreading and the roof from collapsing AS 1684 SPAN TABLES Terminology – Roof Construction Non-coupled roof - a pitched roof that is not a coupled roof. It includes cathedral roofs and roofs constructed using ridge and intermediate beams Such roofs rely 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 AS 1684 SPAN TABLES Using Span Tables ROOF FRAMING AS 1684 SPAN TABLES Roof Framing – 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 cover the footprint while also providing sloping planes able to shed water. Hip Gable (Cathedral or flat ceiling) Skillion Hip and valley Dutch Hip (or Dutch Gable) AS 1684 SPAN TABLES Roof Framing – Typical Members Rafter Ridgeboard Collar tie Top plate Top plate Underpurlin Strut Ceiling joist Strutting beam Strut AS 1684 SPAN TABLES Roof Framing - Transferring loads to Pitched Roof 1. Roofing material takes live/dead/wind loads and transfers them to the Battens. 2. Battens - takes roofing loads and transfers them to the Rafters/Trusses. 3. Rafters – take batten loads and transfers them to the support structure below e.g. walls. Support wall AS 1684 SPAN TABLES Roof Framing – Batten Design Typical Process Step 1: Determine the wind classification to factor in wind loads (e.g. assume non-cyclonic winds N1 or N2) Step 2: Determine type of roof (e.g. tiled or sheet.) Step 3: Determine batten spacing – typically 330 mm for tiles, or 450, 600, 900, 1200 mm sheet Step 4: Determine batten span – this will be the supporting rafter spacing. Batten Batten Span Spacing AS 1684 SPAN TABLES Roof Framing – Batten Design Step 5: Look up relevant Batten Span Table (i.e. noncyclonic winds N1 and N2) in AS1684 Vol. 2. Step 6: Choose a table reflecting preferred stress grade. Step 7: Select column in the table for the previous batten “spacing and span” assumptions. AS 1684 SPAN TABLES Roof Framing – Batten Size Example Inputs required Wind Classification Timber Stress Grade Roof Type Batten Spacing Batten Span = N2 = F8 = Steel Sheet (20 kg/m2) = 900 mm = 900 mm AS 1684 SPAN TABLES Roof Framing – Batten Size Example 2006 Simplify table Wind Classification N2 Roof Type - Steel Sheet (20 kg/m2) Timber Stress Grade F8 Batten Spacing = 900 mm Batten Span = 900 mm A 38 x 75 mm F8 Batten Is adequate AS 1684 SPAN TABLES Rafter Design - Cathedral Roof Scenario Step 1: Determine the wind classification to factor in wind loads. For this example assume non-cyclonic winds N1 or N2. Step 2: Determine dead/live loads on rafters . For this example assume loads are as for a tiled roof with battens (e.g. 60kgs/m2) Step 3: Determine the rafter span. For the example assume a 2100 mm single rafter span. Step 4: Determine the rafter overhang which creates a cantilever span adding extra load. For the example assume a 500 mm overhang. Step 5: Determine the rafter spacing as this determines how much roof loads are shared between rafters. For the example assume a 600 mm spacing . Ridge beam Rafter Spacing AS 1684 SPAN TABLES Rafter Design - Cathedral Roof Scenario Step 6 Look up AS1684 Vol 2 Step 7 Choose table reflecting preferred stress grade Step 8 Determine which column in table to select using the previous “rafter spacing” and “single span” assumptions. Step 9 Go down the column until reaching assumed 2100 mm rafter span and 500 mm overhang Step 10 Check the spans work with assumed roof load of 60kgs/m2 Step 11 Read off rafter size – 90x45mm AS 1684 SPAN TABLES Rafter Design - Cathedral Roof Scenario Inputs required Wind Classification Stress Grade Rafter Spacing Rafter Span Single or Continuous Span Roof Mass (Sheet or Tile) = N2 = F8 = 900 mm = 2200 mm = Single = Steel Sheet (20 kg/m2) Determine Rafter Size 2006 Maximum Rafter or Purlin Span & Overhang (mm) Simplify table A 100 x 50mm F8 rafter is adequate At least 2200mm Inputs required • Wind Classification • Stress Grade • Single or Continuous Span • Rafter Spacing • Rafter Span • Roof Mass (Sheet or Tile) = N2 = F8 = Single = 900 mm = 2200 mm = Steel Sheet (20 kg/m2) AS 1684 SPAN TABLES Ceiling Joist Design Ceiling Joist Design Ridge board Rafter Ceiling Joist Design variables • Timber Stress Grade • Ceiling Joist Spacing • Ceiling Joist Span • Single or Continuous Span AS 1684 SPAN TABLES Ceiling Joist Design Ceiling Joist Design Example Inputs required Wind Classification Stress Grade Overbatten Single or Continuous Span Joist Spacing Ceiling Joist Span = N2 = F17 = No = Single = 450 mm = 3600 mm Ceiling Joist Size 2006 Simplify table Inputs required At least 3600mm A 120 x 45mm F17 ceiling joist is adequate • • • • • • Wind Classification = N2 Stress Grade Overbatten Single or Continuous Span Joist Spacing Ceiling Joist Span = F17 = No = Single = 450 mm = 3600mm AS 1684 Span Tables Ridge board Other Members And Components - Ridge board Some members do not have to be designed using span tables. They are simply called up or calculated based on members framing into them. Member Ridgeboards Hip rafters Application Minimum size (mm) Unstrutted ridge in coupled roof Depth not less than length of the rafter plumb cut 19 thick Strutted ridge in coupled roof with strut spacing not greater than 1800 mm Depth not less than length of the rafter plumb cut 19 thick Strutted ridge in coupled roof with strut spacing greater than 1800 to 2300 mm Depth not less than length of the rafter plumb cut 35 thick Stress grade F11/MGP15 minimum and no less than rafter stress grade 50 greater in depth than rafters 19 thick (seasoned) or 25 thick (unseasoned) Stress grades less than F11/MGP15 50 greater in depth than rafters min. thickness as for rafters Valley rafters Minimum stress grade, as for rafters 50 greater in depth than rafters with thickness as for rafter (min. 35) Valley boards See Note Roof struts (sheet roof) 19 min. thick width to support valley gutter Struts to 1500 mm long for all stress grades 90 45 or 70 70 Struts 1500 to 2400 mm long for all stress grades 70 70 AS 1684 Span Tables 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. AS 1684 Span Tables Roof Member Load Impacts – 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. 0 0 0 0 0 3 5 Wall studs. 1 0 0 Lintels. 5 1 Ridge or intermediate beams. Verandah beams. B Roof Load Widths are measured on the rake of the roof. A AS 1684 Span Tables Roof Member Load Impacts – Roof Load Width AS 1684 Span Tables Roof Member Load Impacts – With Trusses x y x y b a RLW wall B = RLW wall A = 2 2 W L R x RL W y a b A The roof loads on trusses are distributed equally between walls 'A' and 'B'. B AS 1684 Span Tables Roof Member Load Impacts – Without Ridge Struts For a pitched roof without ridge struts it is assumed that some of the load from the un-supported ridge will travel down the rafter to walls 'A' and 'B'. The RLWs for walls A & B are increased accordingly. * * W RL RL W W RL 1 A RL W y x a RL W b 2 3 B x y RLW wall A = a RLW wall B = b 2 2 AS 1684 Span Tables Roof Member Load Impacts – With Ridge Struts RL WR LW RLW y x a 1 A C x Underpurlin 1 = 2 y Underpurlin 2 = 3 y Underpurlin 3 = 3 2 b 3 B AS 1684 Span Tables Roof Member Load Impacts – Ceiling Load Width Ceiling load width (CLW) is the width of ceiling that contributes ceiling load to a supporting member (usually measured horizontally). CLW x A B AS 1684 Span Tables Roof Member Load Impacts – 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 beam span 'x' Hanging Beam Strutting beam Strutting beam span Underpurlin Strutting/Hanging Beam AS 1684 Span Tables Roof Member Load Impacts – Ceiling Load Width FIGURE 2.12 CEILING LOAD WIDTH (CLW) x CLW Hanging beam D = 2 y CLW Strutting/Hanging beam E = 2 EE D D A CLW CLW CLW CLW xx yy B C AS 1684 Span Tables Roof Member Load Impacts – Roof Area Supported Example: The Strutting Beam Span Table requires a ‘Roof Area Supported (m2)’ input. The strutting beam shown supports a single strut that supports an underpurlin. The ‘area required’ is the roof area A/2 supported by the strut. A B/2 B This is calculated as follows:Underpurlin Roof Area Supported = A B 2 2 Sum of half the underpurlin spans either side of the strut (A/2) multiplied by the sum of half the rafter spans either side of the underpurlin (B/2). Strut Strutting Beam Span Strutting Beam AS 1684 Span Tables Strutting Beam Design Example Inputs required Wind Classification Stress Grade Roof Area Supported Strutting Beam Span Single or Continuous Span Roof Mass (Sheet or Tile) = N2 = F8 = 6m2 = 2900 mm = Single = Steel Sheet (20 kg/m2) AS 1684 Span Tables Strutting Beam Design Example Roof Area Supported = 6m2 Roof = Sheet Strutting Beam Span = 2900 mm 2 x 140 x 45 mm F17 members are adequate AS 1684 Span Tables Wall Framing WALL FRAMING Return to menu Return to menu AS 1684 Span Tables Wall Framing Timber or metal bracing Top plate Sheet bracing Common stud Lintel Nogging Wall intersection Bottom plate Jack stud Jamb stud AS 1684 Span Tables Wall Studs Design Example Inputs required Wind Classification Stress Grade Notched 20 mm Stud Height Rafter/Truss Spacing Roof Load Width (RLW) Stud Spacing Roof Type = N2 = MGP10 = Yes = 2400 mm = 900 mm = 5000 mm = 450 mm = Steel Sheet (20 kg/m2) Return to menu Wall Framing – Wall Stud Size 2006 At least 5000mm 70 x 35mm MGP10 wall studs are adequate Simplify table Inputs required • Wind Classification = N2 • Stress Grade • Notched 20 mm • Stud Spacing • Roof Type • Rafter/Truss Spacing= 900 mm • Roof Load Width (RLW) • Stud Height = MGP10 = Yes = 450 mm = Steel Sheet (20 kg/m2) = 5000 mm = 2400 mm AS 1684 Span Tables Top Plate Design Example Inputs required Wind Classification Stress Grade Rafter/Truss Spacing Roof Load Width (RLW) Stud Spacing Roof Type = N2 = MGP10 = 900 mm = 5000 mm = 450 mm = Steel Sheet (20 kg/m2) Return to menu Wall Framing – Top Plate Size 2006 Simplify table 2 x 35x 70mm MGP10 top plates are adequate At least 5000mm Inputs required • Wind Classification = N2 • Stress Grade • Roof Type • Rafter/Truss Spacing= 900 mm • Tie-Down Spacing • Roof Load Width (RLW) • Stud Spacing = MGP10 = Steel Sheet (20 kg/m2) = 900 mm = 5000 mm = 450 mm AS 1684 Span Tables Wall Framing – Wall Lintel Design Example Inputs required Wind Classification Stress Grade Opening size Rafter/Truss Spacing Roof Load Width (RLW) Roof Type = N2 = F17 = 2400 mm = 900 mm = 2500 mm = Steel Sheet (20 kg/m2) Wall Framing – Lintel Size 2006 Simplify table A 140 x 35mm F17 Lintel is adequate Use 1200mm Inputs required • Wind Classification = N2 • Stress Grade • Roof Type • Roof Load Width (RLW) • Rafter/Truss Spacing= 900 mm • Opening size = F17 = Steel Sheet (20 kg/m2) = 2500 mm Use 3000mm = 2400 mm AS 1684 Span Tables Floor Framing FLOOR FRAMING Return to menu AS 1684 Span Tables Floor Framing – Floor Members Floor joists Floor bearers Platform Floor Sheets Perimeter Brickwork AS 1684 Span Tables Floor Framing – 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 3.6m) grid Be are rs pa ci n g Bearer Spacing r are Be n spa Bearer Span AS 1684 Span Tables Floor Framing – Floor Load Width Example If a = 900 mm x = 2000 mm y = 4000 mm FLW A = 1900 mm FLW B = 3000 mm FLW C = 2000 mm AS 1684 Span Tables Floor Framing – Bearer and Floor Joist Example Simple rectangular shaped light-weight home Gable Roof =25o pitch Steel Sheet = 20 kg/m2 Wind Speed = N2 Floor joists Wall Height = 2400 mm Bearers 3600 Section 4500 Elevation AS 1684 Span Tables Floor Framing – Bearer Design Example Floor Load Width (FLW) Bearers at 1800 mm centres FLWA = 1800/2 = 900 mm Bearer A Supports both a Roof Load And a floor load Floor Joists at 450 mm crs 1800 3600 Section AS 1684 Span Tables Floor Framing – Bearer Design Example x y a 2 Roof Load Width (FLW) for Wall A = a = 496 mm x = 1986 mm Total RLW On Wall A = 1986 mm (say 2000 mm) + 496 mm (say 500 mm) = 2500 mm W RL x RL W y a b A B AS 1684 Span Tables Floor Framing – Bearer Design Example Inputs required • Wind Classification • Stress Grade • Floor Load Width (FLW) at A • Roof Load Width (RLW) • Single or Continuous Span • Roof Mass (Sheet or Tile) • Bearer Span = N2 = F17 = 900 mm = 2500 mm = Continuous = Steel Sheet (20 kg/m2) = 1800 mm Floor Framing – Bearer Size 2006 Simplify table Inputs required • Wind Classification = N2 • Stress Grade • Floor Load Width (FLW) at A • Roof Mass (Sheet or Tile) • • Single or Continuous Span Roof Load Width (RLW) Bearer Span 2 x 90 x 35mm F17 members joined together are adequate = F17 = 900 mm = Steel Sheet (20 kg/m2) = Continuous = 2500 mm = 1800mm Use 1200mm table Use 4500mm AS 1684 Span Tables Floor Joist Design Example Inputs required Wind Classification Stress Grade Roof Load Width (RLW) (just supporting floor loads) Single or Continuous Span Roof Type Joist Spacing = N2 = F17 = 0 mm = Continuous (max 1800) = Steel Sheet (20 kg/m2) = 450 mm Floor Framing – Floor Joist Design Example 2006 Simplify table 90 x 35mm F17 floor joists at 450mm crs are adequate At least 1800mm Inputs required Wind Classification = N2 Stress Grade = F17 Joist Spacing = 450 mm Roof Type = Steel Sheet (20 kg/m2) Single or Continuous Span = Continuous (max 1800) Roof Load Width (RLW) = 0 mm Joist span = 1800mm Further Information Visit www.WoodSolutions.com.au For more than three thousand pages of information, inspiration and technical publications on everything about timber in the built environment. 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