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TIMBER FRAMING USING AS 1684.2 SPAN TABLES

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Title: TIMBER FRAMING USING AS 1684.2 SPAN TABLES


1
TIMBER FRAMINGUSING AS 1684.2 SPAN TABLES
AS 1684 Teaching Guide
2
AS 1684-2010 Residential timber-framed
construction
AS 1684-2010 Residential timber-framed
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.

3
the timber framing standard
AS 1684 RESIDENTIAL TIMBER-FRAMED CONSTRUCTION
Currently you should be using the 2010 Edition.
4
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).
5
AS 1684.2 CD Span Tables
AS 1684 TIMBER-FRAMING STANDARD
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
6
AS 1684 TIMBER-FRAMING STANDARD
Each set of Span Tables contains 53 separate
design tables
7
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.
8
AS 1684 TIMBER-FRAMED CONSTRUCTION
Ridge beam
Battens
Rafters
Hanging beams
Ceiling battens
Ceiling
First floor wall frames
Roofing
External cladding
Floor joists
Ceiling battens
Flooring
Lintel
Wall frame
Wall stud
Internal cladding
Floor joists
Flooring
Bearers
Stumps or piles
9
AS 1684 Scope and Limitations
  • WHERE CAN AS1684 BE USED?

10
AS 1684 Physical Limitations -
  • 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)

11
AS 1684 Physical Limitations - Width
Width
The geometric limits of the span tables often
will limit these widths.
12
Wall Height
AS 1684 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).
13
Design Forces on Buildings
AS 1684 Physical Limitations Design Forces on
Buildings
AS1684 can be used to design for Gravity Loads
(dead live) and wind loads.
(a)  Gravity loads
(b)  Wind loads
14
Wind Classification
AS 1684 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
15
Wind Classification
AS 1684 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.)

16
AS 1684 Wind Classification Simple References
Geographic Region A
Site Location Top ? of hill or ridge Below top ? of hill or ridge
Suburban site Not within two rows of City or Town perimeter (as estimated 5 years hence) Open areas larger than 250,000 m2 N2 N1
Less than 250m from the sea open water wider than 250m N3 N2
Within two rows of City or Town perimeter (as estimated 5 years hence) Open areas larger than 250,000 m2 N3 N2
Rural areas N3 N2
17
AS 1684 Using Span Tables
Design fundamentals basic terminology Roof
framing Wall framing Floor framing (Click on
arrow to move to section required)
18
AS 1684 Using Span Tables
DESIGN FUNDAMENTALS BASIC TERMINOLOGY
19
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.
20
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.
21
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.

22
AS 1684 SPAN TABLES Design Fundamentals Load
Distribution
Loads distributed
Loads are distributed equally between Points of
Support. 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.
23
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.
A
C
A
B
B
C
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
24
AS 1684 SPAN TABLES Terminology Span
Terminology - Span and Spacing
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
25
AS 1684 SPAN TABLES Terminology Single Span
The span of a member supported at or near both
ends with no immediate supports. This includes
the case where members are partially cut through
over intermediate supports to remove spring.
26
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.
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.
27
AS 1684 SPAN TABLES Continuous Span Example
Example Continuous Span
Span 2 is not to be greater than twice Span
1. This span is used to determine the size using
the Continuous Span tables.
28
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.
Rafter
29
AS 1684 SPAN TABLES Design Fundamentals Spacing
Terminology - Span and 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).
30
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.).
31
AS 1684 SPAN TABLES Terminology Roof
Construction
Terminology Roof Construction
Coupled Roof - rafters are tied together by
ceiling joists so that they cannot spread.
32
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.
33
AS 1684 SPAN TABLES Using Span Tables
ROOF FRAMING
34
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)
35
AS 1684 SPAN TABLES Roof Framing Typical Members
36
AS 1684 SPAN TABLES Roof Framing - Transferring
loads to Pitched Roof
Support wall
37
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.

38
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.
39
AS 1684 SPAN TABLES Roof Framing Batten Size
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
AS 1684 SPAN TABLES Roof Framing Batten Size
Example
Simplify table
Wind Classification N2
Roof Type - Steel Sheet (20 kg/m2)
Timber Stress Grade F8
A 38 x 75 mm F8 Batten Is adequate
Batten Spacing 900 mm
Batten Span 900 mm
41
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 .

42
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
43
AS 1684 SPAN TABLES Rafter Design - Cathedral
Roof Scenario
  • 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
Determine Rafter Size
Simplify table
Maximum Rafter or Purlin Span Overhang (mm)
  • Inputs required
  • Wind Classification N2
  • Stress Grade F8
  • Single or Continuous Span Single
  • Rafter Spacing 900 mm
  • Rafter Span 2200 mm
  • Roof Mass (Sheet or Tile) Steel Sheet
  • (20 kg/m2)

A 100 x 50mm F8 rafter is adequate
45
Ceiling Joist Design
AS 1684 SPAN TABLES Ceiling Joist Design
  • Design variables
  • Timber Stress Grade
  • Ceiling Joist Spacing
  • Ceiling Joist Span
  • Single or Continuous Span

46
Ceiling Joist Design
AS 1684 SPAN TABLES 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
Simplify table
  • Inputs required
  • Wind Classification N2
  • Stress Grade F17
  • Overbatten No
  • Single or Continuous Span Single
  • Joist Spacing 450 mm
  • Ceiling Joist Span 3600mm

A 120 x 45mm F17 ceiling joist is adequate
48
AS 1684 Span Tables Other Members And Components
- Ridge board
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.
49
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.

50
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.
  • Roof Load Widths are measured on
  • the rake of the roof.

51
AS 1684 Span Tables Roof Member Load Impacts
Roof Load Width
52
AS 1684 Span Tables Roof Member Load Impacts
With Trusses
RLW wall A
53
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 wall A
RLW wall B
54
AS 1684 Span Tables Roof Member Load Impacts
With Ridge Struts
x
2
55
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).
56
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
Hanging Beam
Strutting/Hanging Beam
57
AS 1684 Span Tables Roof Member Load Impacts
Ceiling Load Width
FIGURE  2.12   CEILING LOAD WIDTH (CLW)
58
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 supported by
the strut.
59
AS 1684 Span Tables 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)
60
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
61
AS 1684 Span Tables Wall Framing
Return to menu
WALL FRAMING
62
AS 1684 Span Tables Wall Framing
Return to menu
63
AS 1684 Span Tables Wall Studs Design Example
Return to menu
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)
64
Wall Framing Wall Stud Size
Simplify table
  • Inputs required
  • Wind Classification N2
  • Stress Grade MGP10
  • Notched 20 mm Yes
  • Stud Spacing 450 mm
  • Roof Type Steel Sheet (20 kg/m2)
  • Rafter/Truss Spacing 900 mm
  • Roof Load Width (RLW) 5000 mm
  • Stud Height 2400 mm

70 x 35mm MGP10 wall studs are adequate
65
AS 1684 Span Tables Top Plate Design Example
Return to menu
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)
66
Wall Framing Top Plate Size
  • Inputs required
  • Wind Classification N2
  • Stress Grade MGP10
  • Roof Type Steel Sheet (20 kg/m2)
  • Rafter/Truss Spacing 900 mm
  • Tie-Down Spacing 900 mm
  • Roof Load Width (RLW) 5000 mm
  • Stud Spacing 450 mm

2 x 35x 70mm MGP10 top plates are adequate
67
AS 1684 Span Tables Wall Framing 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)
68
Wall Framing Lintel Size
  • Inputs required
  • Wind Classification N2
  • Stress Grade F17
  • Roof Type Steel Sheet (20 kg/m2)
  • Roof Load Width (RLW) 2500 mm
  • Rafter/Truss Spacing 900 mm
  • Opening size 2400 mm

A 140 x 35mm F17 Lintel is adequate
69
AS 1684 Span Tables Floor Framing
Return to menu
FLOOR FRAMING
70
AS 1684 Span Tables Floor Framing Floor Members
Floor joists
Floor bearers
Platform Floor Sheets
Perimeter Brickwork
71
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
Bearer Span
Bearer Spacing
72
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
73
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
  • Wall Height 2400 mm

Elevation
74
AS 1684 Span Tables Floor Framing Bearer Design
Example
25o
Floor Load Width (FLW) Bearers at 1800 mm
centres FLWA 1800/2 900 mm
Bearer A
Supports both a Roof Load
Floor Joists at 450 mm crs
And a floor load
75
AS 1684 Span Tables Floor Framing Bearer Design
Example
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
76
AS 1684 Span Tables Floor Framing 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 1800 mm

77
Floor Framing Bearer Size
Simplify table
2 x 90 x 35mm F17 members joined together are
adequate
  • Inputs required
  • Wind Classification N2
  • Stress Grade F17
  • Floor Load Width (FLW) at A 900 mm
  • Roof Mass (Sheet or Tile) Steel Sheet
    (20 kg/m2) Single or Continuous
    Span Continuous
  • Roof Load Width (RLW) 2500 mm
  • Bearer Span 1800mm

78
AS 1684 Span Tables 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
79
Floor Framing Floor Joist Design Example
90 x 35mm F17 floor joists at 450mm crs are
adequate
  • 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

80
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