AS 1684 Teaching Guide

TIMBER FRAMING USING AS 1684.2 SPAN TABLES

• • • • 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

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

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 Rafters Ceiling Roofing Floor joists Flooring Wall frame Floor joists Stumps or piles Battens Hanging beams Ceiling battens First floor wall frames External cladding Ceiling battens Lintel Wall stud Internal cladding Flooring Bearers

AS 1684 Scope and Limitations WHERE CAN AS1684 BE USED?

AS 1684 Physical Limitations -

Plan: Rectangular, square or “L”-shaped Storeys: Single and two storey construction Pitch: 35 o 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 garage roof.

Pitching Point of verandah or patio roof.

Garage Main house Verandah or Patio

16.0 m max.

16.0 m max.

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) Internal pressure LIVE LOADS (people, furniture etc.) Wind 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 N3 - W41N N4 - W50N 120km/h gust 150km/h gust 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 m 2 • • 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 m 2 Rural areas Top ⅓ of hill or ridge Below top ⅓ of hill or ridge N2 N1 N3 N2

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

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.

Indirect Load path due to cantilever Roof Load Ground level

AS 1684 SPAN TABLES 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

A A B B

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

C C

Terminology - 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 l ap Si ngle span Si ngle 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.

Cont inuous span Cont inuous 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

1/3 (2000 mm) 6000 mm 1/3 (2000 mm) The center support must be wholly within the middle third.

1/3 (2000 mm) 75 mm  Span 1 (2000 mm) 75 mm Span 2 (3925 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.

Ra fte r s pa n Ov erh an g Rafter

Terminology - 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 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

otherwise there is nothing to stop the walls from spreading and the roof from collapsing 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

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 Intermediate Beam Rafter

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

Top plate Rafter Strut Ridgeboard Collar tie Top plate Underpurlin 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.

3. Rafters – take batten loads and transfers them to the support structure below e.g. walls.

2. Battens - takes roofing loads and transfers them to the Rafters/Trusses.

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. non cyclonic 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  = N2 Timber Stress Grade = F8  Roof Type = Steel Sheet (20 kg/m 2 )  Batten Spacing = 900 mm  Batten Span = 900 mm

AS 1684 SPAN TABLES Roof Framing – Batten Size Example

2006 Simplify table Wind Classification N2 Roof Type - Steel Sheet (20 kg/m 2 ) 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/m 2 ) 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/m 2 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/m 2 )

Determine Rafter Size 2006 Maximum Rafter or Purlin Span & Overhang (mm) Simplify table A 100 x 50mm F8 rafter is adequate At least 2200 mm • • • • • •

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 At least 3600 mm A 120 x 45mm F17 ceiling joist is adequate Simplify table • • • • • •

Inputs required

Wind Classification Stress Grade Overbatten = N2 Single or Continuous Span Joist Spacing Ceiling Joist Span = F17 = No = Single = 450 mm = 3600mm

AS 1684 Span Tables

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 Valley rafters Valley boards Roof struts (sheet roof)

Application

Unstrutted ridge in coupled roof Strutted ridge in coupled roof with strut spacing not greater than 1800 mm Strutted ridge in coupled roof with strut spacing greater than 1800 to 2300 mm Stress grade F11/MGP15 minimum and no less than rafter stress grade Stress grades less than F11/MGP15 Minimum stress grade, as for rafters See Note

Minimum size (mm)

Depth not less than length of the rafter plumb cut  19 thick Depth not less than length of the rafter plumb cut  19 thick Depth not less than length of the rafter plumb cut  35 thick 50 greater in depth than rafters  19 thick (seasoned) or 25 thick (unseasoned) 50 greater in depth than rafters  min. thickness as for rafters 50 greater in depth than rafters with thickness as for rafter (min. 35) 19 min. thick  width to support valley gutter Struts to 1500 mm long for all stress grades Struts 1500 to 2400 mm long for all stress grades 90  45 or 70 70  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.

 Wall studs.

 Lintels.

 Ridge or intermediate beams.

 Verandah beams.

300 0 150 0 150 0 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

RLW wall A =

x

 2

y



a

RL W

x

a RLW wall B =

x

 2

y



b

y

RLW 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.

* * RLW RL W RL W RLW RLW

x y

a

1 2

b

3

RLW wall A =

A

x

2 

a

B

RLW wall B =

y

2 

b

AS 1684 Span Tables Roof Member Load Impacts – With Ridge Struts

a RL W

x 1 2

RLW RLW

y

b

3

A

Underpurlin 1 Underpurlin 2 Underpurlin 3 =

x

C 2

y

=

3

y

=

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 'x' Hanging Beam Hanging beam span Roof strut Strutting beam span Strutting beam 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 D

D

x

x y

y

AS 1684 Span Tables Roof Member Load Impacts – Roof Area Supported

Example: The Strutting Beam Span Table requires a ‘Roof Area Supported (m 2 )’ input. The strutting beam shown supports a single strut that supports an underpurlin. The ‘area required’ is the roof area

A/2 Underpurlin

supported by the strut.

A B/2

This is calculated as follows:-

Roof Area Supported = A 2



B 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).

Strutting Beam Span

B Strut 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 = 6m 2 = 2900 mm = Single = Steel Sheet (20 kg/m 2 )

AS 1684 Span Tables Strutting Beam Design Example

Roof Area Supported = 6m 2 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

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AS 1684 Span Tables Wall Framing

Timber or metal bracing Common stud Nog ging Wall intersection Jack stud Jamb stud Top plate Lintel She et bracin g Bottom pla te

AS 1684 Span Tables Wall Studs Design Example Inputs required

Wind Classification Stress Grade Notched 20 mm = N2 = MGP10 = Yes Stud Height Rafter/Truss Spacing = 2400 mm = 900 mm Roof Load Width (RLW) = 5000 mm Stud Spacing Roof Type = 450 mm = Steel Sheet (20 kg/m 2 ) Return to menu

Wall Framing – Wall Stud Size 2006 70 x 35mm MGP10 wall studs are adequate At least 5000 mm 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 = N2 = MGP10 Rafter/Truss Spacing = 900 mm Roof Load Width (RLW) = 5000 mm Stud Spacing Roof Type = 450 mm = Steel Sheet (20 kg/m 2 ) Return to menu

Wall Framing – Top Plate Size 2006

Simplify table 2 x 35x 70mm MGP10 top plates are adequate At least 5000 mm • • • • • • •

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 = N2 = F17 = 2400 mm Rafter/Truss Spacing = 900 mm Roof Load Width (RLW) = 2500 mm Roof Type = Steel Sheet (20 kg/m 2 )

Wall Framing – Lintel Size

2006 Simplify table A 140 x 35mm F17 Lintel is adequate Use 1200 mm • • • • • •

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 3000 mm = 2400 mm

AS 1684 Span Tables Floor Framing FLOOR FRAMING

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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 Bea rer spa cin Bearer Spacing Be are r s pa n 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 =25 o pitch  Steel Sheet = 20 kg/m 2  Wind Speed = N2  Wall Height = 2400 mm

Bearers Floor joists 3600 Section 4500 Elevation

AS 1684 Span Tables Floor Framing – Bearer Design Example

Floor Load Width (FLW) Bearers at 1800 mm centres FLW A = 1800/2 = 900 mm Bearer A Supports both a Roof Load And a floor load

1800 3600 Section

Floor Joists at 450 mm crs

AS 1684 Span Tables Floor Framing – Bearer Design Example

Roof Load Width (FLW) for Wall A =

x

 2

y



a

a = 496 mm x = 1986 mm Total RLW On Wall A = 1986 mm (say 2000 mm) + 496 mm (say 500 mm) = 2500 mm RL W

x y

RLW a b

A B

AS 1684 Span Tables Floor Framing – Bearer Design Example

• • • • • • •

Inputs required

Wind Classification Stress Grade = N2 = 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/m 2 ) Bearer Span = 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 = F17 = 900 mm = Steel Sheet (20 kg/m2) = Continuous = 2500 mm = 1800mm 2 x 90 x 35mm F17 members joined together are adequate Use 1200 mm table Use 4500 mm

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/m 2 ) = 450 mm

Floor Framing – Floor Joist Design Example

2006 Simplify table 90 x 35mm F17 floor joists at 450mm crs are adequate At least 1800 mm     Inputs required  Wind Classification = N2  Stress Grade  Joist Spacing Roof Type Single or Continuous Span Roof Load Width (RLW) Joist span = F17 = 450 mm = Steel Sheet (20 kg/m2) = Continuous (max 1800) = 0 mm = 1800mm

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