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WoodSolutions Teaching Resource

AS 1684 – 2010 Annotated Standard

Section 2 Terms & Definitions 2010


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Teaching Guide AS 1684.2&3 2-1


SECTION 2: TERMINOLOGY AND DEFINITIONS

2.1 GENERAL The terminology and definitions given in this Section shall be used in conjunction with the requirements of this Standard. The terminology used by the building industry varies greatly between states, regions within states and even between those working in the same region. Where possible, the more commonly used terms have been adopted by this standard. 2.2 TERMINOLOGY OF FRAMING MEMBERS Figure 2.1 details floor, wall and ceiling framing members in general. An alternative wall frame detail is given in Figure 6.1(b). Figures 2.2 to 2.7 apply to roof framing.

Rafter

Fascia

Lintel

Ledger

Jack stud

Sill trimmer

Jamb stud

Jack stud

Soffit bearer

Termite shield(ant cap)

Cleat (hanger)

Hanging beam

Ceiling joist

Jack ceiling joist(trimmer)

Top wall plate

Brace

Nogging

Common stud

Bottom wall plate

Floor joist

Bearer

Stump (post, pier)

NOTE: The ceiling and floor joists are shown parallel to the external loadbearing wall for clarity. The more

usual case in practice is for the joists to be located perpendicular to the external wall. Lintel location may also vary (see Figure 6.8).

FIGURE 2.1 FRAMING MEMBERS—FLOOR, WALL AND CEILING



Fascia

Raking plate

Solid blocking

Bargeboard(verge, verge rafter)

Outrigger

Top plate

Ceiling joist

Underpurl in

Collar t ie

Common rafter

Ridgeboard

NOTE: Some members have been omitted for clarity.

FIGURE 2.2 FRAMING MEMBERS—GABLE ROOF CONSTRUCTION

Top plate

Creeper rafter

Val ley rafter

Jack rafter (crown end)

Cripple creeper rafter

Broken hipRidgeboard

Hip rafter

Creeper rafter

Hip rafter

Jack cei ling joist

Rafter

Cei ling joist

Roof strut

Underpurlin

Hanging beam

Valley creeper rafter

Col lar t ie

Jack rafter (crown end)

Fascia 190 x 19 min.


FIGURE 2.3 FRAMING MEMBERS—HIP AND VALLEY ROOF CONSTRUCTION



Top plate

Rafter

Val ley creeper rafter

Scotch valley(pitching plate)

Fascia

Rafter

Cei ling joist

Ridgeboard


FIGURE 2.4 FRAMING MEMBERS—SCOTCH VALLEY CONSTRUCTION

Ridge beam

Studs support ingconcentrationsof loads

Intermediate beam

Rafter support ingroof and ceiling loads ( ) roof beam

Eaves beam

Raking top plate

Verge rafter


FIGURE 2.5 FRAMING MEMBERS—CATHEDRAL ROOF CONSTRUCTION



Fascia

Raking plate

Sol idblocking

Bargeboard(verge, verge rafter)

Outrigger

Bargeboard

Top plate

FIGURE 2.6 SKILLION ROOF

Standard truss

Structural fascia

Raking truss(gable t russ)

Verge overhang

End wall

Outr iggers

Gable end stud

Barge(verge rafter)

NOTE: This diagram applies to verge overhangs greater than 300 mm from the raking or gable truss

(see AS 4440).

FIGURE 2.7 GABLE END—TRUSSED ROOF

2.3 VERTICAL LAMINATION 2.3.1 Vertical nail lamination Vertical nail lamination shall be permitted to achieve the required breadth for the larger section sizes given in the Span Tables of the Supplements using thinner and more readily obtainable sections. This is only permissible using seasoned timber laminations of the same timber type (e.g. hardwood + hardwood, softwood + softwood) and stress grade. Laminations shall be unjoined in their length. Nails shall be a minimum of 2.8 mm in diameter and shall be staggered as shown in Figure 2.8(a), and shall be through-nailed and clinched, or nailed from both sides.



Where screws are used in lieu of nails, they shall be minimum No. 10 screws at the same spacing and pattern, provided that they penetrate a minimum of 75% into the thickness of the final receiving member. 2.3.2 Lamination of spaced ring beams

Ring beams that are made up of two spaced members shall be laminated in accordance

with Figure 2.8(b)

(a) Vertical nail lamination (strutting beam shown)

(b) Lamination of spaced ring beams

FIGURE 2.8 VERTICAL LAMINATION



FIGURE 2.8 VERTICAL NAIL LAMINATION (EXAMPLE—STRUTTING BEAMS)

NOTE: Top plate are an exception to the rule and can be ‘horizontally nail laminated’

i.e. with the load in line with the nails. Refer Clause 2.5. The multiple member sizes given in the Span tables take into consideration the reduced effectiveness of this type of nail laminated.

2.4 STUD LAMINATION The required size may be built up by using two or more laminations of the same timber type, (e.g. hardwood + hardwood, softwood + softwood) stress grade and moisture content condition, (an unseasoned stud can NOT be laminated to a seasoned stud) provided the achieved width is at least that of the nominated size. Studs up to 38 mm thick shall be nailed together with one 75 mm nail at maximum 600 mm centres. Studs over 38 mm but not exceeding 50 mm thick shall be nailed with one 90 mm nail at maximum 600 mm centres (see Figure 2.9).

The term 'vertical nail lamination' is used because the loads applied to a house frame are predominantly vertical.

The load applied to nail laminated timber must always be in the direction

of the depth of the timber and at 90 to the nails.

O

Direction of load

Direction of load

If the load on a nail laminated member is in the opposite direction to the depth and in line with the nails, the nails will be insufficient to prevent movement between the two pieces. Due to this movement or 'slippage' between the pieces they will act individually rather than as a single member. .

Load

Load

Movement occurs between the pieces

There are few situations in a house frame where the main direction of load on a member is horizontal. Generally horizontal loads are the result of wind or earthquake loads. Sill trimmers are perhaps the only structural member where the only real load is due to wind. Horizontal wind loads in high wind areas on studs may govern studs sizes.

Studs are nail laminated as per Clause 2.4 and window sill/lintel trimmers are nail laminated as per wall plates Clause 2.5.

Direction Of load

Direction of load

The nail size and spacing that applies to 'vertical nail lamination' is also applicable to members used horizontally where the direction of the applied load is horizontal.



Where screws are used in lieu of nails, they shall be minimum No. 10 screws at the same spacing and pattern, provided that they penetrate a minimum of 75% into the thickness of the final receiving member. Posts shall not be nail-laminated.

Multiple studs nailed together at 600 mm max. centres

600 max.

Plates nai led togetherover each stud

Joints min. 1200 mm apart and staggered

Where joints occur in either top plate between studs, and where rafter or truss bears onto top plates, addit ional blocking shall be provided

NOTE: Refer to Section 9 for other nominal fixing requirements including plates to studs.

FIGURE 2.9 STUD/PLATE LAMINATION

2.5 HORIZONTAL NAIL LAMINATION — WALL PLATES ONLY

Wall plates that are made up of more than one section (e.g. 2/35 70) shall be horizontally nail-laminated in accordance with Figure 2.9 and using – (a) two 75 mm long nails for plates up to 38 mm deep, or (b) two 90 mm long nails for plates up to 50 mm deep (see also Clause 9.2.10). A minimum of two nails shall be installed at not greater than 600 mm centres along the plate. Where more than two plates are used, the nailing requirement applies to each lamination

Posts are not to be nail laminated because they do not have the lateral restraint in the opposite direction to the lamination that studs receive from nogging.

Lateral restraint from noggingNo lateral restraint

POST STUD



All joins in multiple bottom plates shall occur over solid supports such as floor joists, solid blocking between bottom plate and bearer or concrete slab.

2.6 LOAD WIDTH AND AREA SUPPORTED 2.6.1 General The load width and area supported are used to define the amount of dead, live and wind load that is imparted onto a member. Load width, coupled with another geometric descriptor such as spacing or span will define an area of load that a member is required to support. To determine a timber size for a particular member, the amount of dead & live load that is to be applied to that member must be determined prior to entering the span tables. The amount of load is directly proportional to the AREA of roof and/or floor that this member supports.

For most members, this AREA is not actually calculated but “Load width, .. plus.. another geometric descriptor such as spacing (or span) will define an area of load that a member is required to support”. Note: Uplift loads in high wind areas may dictate the size of a member. The magnitude of the uplift load will (generally) be in proportion to the area that is supported. Floor load width (FLW), ceiling load width (CLW) and roof load width (RLW) shall be determined from Clauses 2.6.2 to 2.6.4.

Joins in adjacent plates are to be a minimum of 1200 mm apart. Joins in either plate may be made between studs. (see Clause 9.2.10 & Figure 9.2 (c)

If a loadbearing member falls between studs where either plate is joined, the plates must be reinforced with an additional piece of timber of the same size as the individual plate being reinforced. (also refer Clause 6.2.2.3)

Ribbonplate

construction

1200 mm min between joins

2/75 x 3.05 mm nailseither side off joins.

2/75 x 3.05 mm nailsat each stud.

To avoid splitting, nails can be offset to the sides of studs by 50 mm.

Blocking piece required if a rafter, truss, floor joist or other point load falls between the studs where a join occurs. Blocking will also be required if any uplift loads fall between tie-down points where a join occurs.

50 mm



For uplift due to wind loads, the definition ‘uplift load width’ (ULW) is used as ULWs may differ significantly from RLWs depending upon where the structure is tied down. Refer to Section 9 for definition of ULW. For most houses, the ‘uplift load width’ and ‘roof load width’ is measured between the same points. The actual measurements will vary however because RLW is measured on the rake of the roof between the two points and ULW is measured horizontally between the same points.

There are occasionally situations where the points of measurement of ULW ‘may differ significantly’ from the points for RLW. Such cases are discussed in Section 9. 2.6.2 Floor load width (FLW) Floor load width (FLW) is the contributory width of floor, measured horizontally, that imparts floor load to a supporting member. FLW shall be used as an input to Span Tables in the Supplements for all bearers and lower storey wall framing members. The FLW input is illustrated in Figures 2.10 and 2.11. Of the total load on a floor joist, half will go to the bearer on one end and half to the bearer on the other end. So floor load width (FLW) is simply half the floor joist span on either side of the bearer, added together. The only exception is where there is a cantilever. In this situation, the total cantilever distance plus half of the floor joist span is used.

Type of construction Location Floor load width

(FLW)

(a)

Ca

nti

leve

red

ba

lco

ny

A B C

yxa

FLW FLW FLW

Bearer A FLW = ax

2

Bearer B FLW =2

yx

Bearer C FLW =2

y

(b)

Su

pp

ort

ed

ba

lco

ny

A B C D

zyx

FLW FLW FLW FLW

Bearer A FLW =2

x

Bearer B FLW =2

yx

Bearer C FLW =2

zy

Bearer D FLW =2

z

FIGURE 2.10 FLOOR LOAD WIDTH (FLW)—

SINGLE OR UPPER-STOREY CONSTRUCTION



A B C D

a x y z

FLW FLW FLW

FLW FLW FLW FLW

Type of construction Location Floor load width (FLW)

(a) Lower storey loadbearing walls

Wall A Upper FLW = ax

2

Wall B Upper FLW =2

yx

Wall C Upper FLW =2

y

Wall D N/A*

(b) Bearers supporting lower storey loadbearing walls

Bearer A

Upper FLW = ax

2

Lower FLW =2

x

Bearer B

Upper FLW =2

yx

Lower FLW =2

yx

Bearer C

Upper FLW =2

y

Lower FLW =2

zy

Bearer D

Upper FLW = N/A*

Lower FLW =2

z

* See single or upper-storey construction.

FIGURE 2.11 FLOOR LOAD WIDTH (FLW)—TWO-STOREY CONSTRUCTION

Examples of calculating and applying FLW to the span tables are given in Section 4 – Floor Framing.



2.6.3 Ceiling load width (CLW) Ceiling load width (CLW) is the contributory width of ceiling, usually measured horizontally, that imparts ceiling load to a supporting member. CLW shall be used as an input to Span Tables for hanging beams, counter beams and strutting/hanging beams. The CLW input is illustrated in Figure 2.12. Ceiling load width (CLW) is simply the sum of half the ceiling joist spans on each side of the Hanging beam or Strutting/ hanging beam.

A B C

D E

x y

CLW CLW

Location Ceiling load width

(CLW)

Walls A, B & C N/A*

Beam D

(Hanging beam) CLW =

2

x

Beam E

(Strutting/hanging

beam)

CLW =2

y

* CLW is not required as an input to the

Tables for wall framing or bearers

supporting loadbearing walls.

FIGURE 2.12 CEILING LOAD WIDTH (CLW) * CLW is not required as an input to the Tables for wall framing or bearers supporting loadbearing walls – because these loads are already included in the ‘Sheet’ or ‘Tile’ roof loads required as input to the tables for these members. 2.6.4 Roof load width (RLW) The roof load width (RLW) is used as a convenient indicator of the roof loads that are carried by some roof members and loadbearing wall members and their supporting substructure. The RLW value shall be used as an input to the relevant wall framing and substructure Span Tables. Figures 2.13 to 2.16 define RLW in relation to various types of

roof construction. Of the roof load on members such as rafters and trusses, half will go to the supporting wall or beam on one end and half to the supporting wall or beam on the other end. So roof load width (RLW) is simply half the particular member’s span, plus any overhang, measured on the rake of the roof.



NOTE: Amendment 1, deleted reference to RLW’s in the diagrams in Figures 2.13 and 2.14 but they have been retained below for clarity.

Type of construction Wall Roof load width (RLW)

for member sizing

(a)

Tru

ss

A

RLW = ayx

2

B

RLW = byx

2

A

RLW = ayx

2

B

RLW = byx

2

(b)

Ca

the

dra

l

A

RLW = ax

2

B

RLW = by

2

C RLW =2

yx

(c)

Skillio

n

A

RLW = ax

2

B RLW = bx

2

FIGURE 2.13 ROOF LOAD WIDTH (RLW)—NON-COUPLED ROOFS

x y

a b

A B

RLW RLW

The roof loads on trusses are distributed equally between walls 'A' and 'B'.

x y

a b

A B

RLW RLW

The roof loads on trusses with unequal pitches are also distributed equally between walls 'A' and 'B'.

A C B

x y

a b

RLW

RLW + RLW

RLW

x

a

b

A B

RLW

RLW

The roof loads on rafters in a cathedral or skillion roof are distributed equally between the wall or beam on either end of the rafter.




for member sizing

(a) No ridge struts

A RLW = x + a

B RLW = y + b

(b) Ridge struts

Although it states that a RLW is not applicable (N/A) for wall ‘C’, a measurement equal to the ‘RLW’ shown above and calculated on the right, will be required to calculated the area supported by the ‘studs supporting concentrated loads’ in wall ‘C’

A

RLW = ax

2

B

RLW = by

2

C N/A*

* RLW may not be applicable where strut loads are supported by studs supporting concentrations

of load and the remainder of wall C is deemed non-loadbearing. In this case, the roof area

supported shall be determined for the studs supporting concentrated loads.

FIGURE 2.14 ROOF LOAD WIDTH (RLW)—COUPLED ROOFS

WITH NO UNDERPURLINS

xy

a b

A B

RLWRLW

x y

a b

A C B

RLW

RLW + RLW

RLW

RLW = x y

2 2+




for member sizing

(a) No ridge struts

A

RLW = a

x

2

B RLW = by

3

RWL =

RLW =

RLW =

(b) Ridge struts

A

RLW = ax

4

B

RLW = by

6

C

N/A*

RLW =

RLW =

RLW =

* RLW may not be applicable where strut loads are supported by studs supporting concentrations of load and the remainder of wall C is deemed non-loadbearing. In this case the roof area supported shall be determined for the studs supporting concentrated loads.

NOTES: Collar ties have been omitted for clarity.

FIGURE 2.15 ROOF LOAD WIDTH (RLW)—COUPLED ROOFS WITH UNDERPURLINS

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 RLW's for these walls are increased accordingly.

xy

a b

A B

RLW RLWRLW RLW

RLW

21

3

x

2

y

3

y

3

1

2

3

Although RLW's are not shown for the underpurlins these RLW's are required by the underpurlin span table and also to calculate the area supported by the ‘studs supporting concentrated loads’ at the end of struts and/or strutting beams that support the underpurlins.

x y

a b

A C B

RLWRLW

RLW + RLWRLW

RLWRLW

31 2

RLW = x y

4 6+

Although it states that a RLW is not applicable (N/A) for wall 'C' or the underpurlins, these RLW's will be required to calculate the area supported by the 'studs supporting concentrated loads' in wall 'C' and at the end of struts and/or strutting beams that support the underpurlins.

x

2

y

3

y

3

1

2

3




for member sizing

a) Cathedral — Framed

A RLW = ax

4

B RLW = by

6

C RLW =64

yx

Cathedral — Truss

A RLW = ax

2

B RLW = by

2

C RLW =2

yx

(c) Verandah

A RLW = av

2

B RLW =RLW for main roof +2

v

NOTE: Collar ties have been omitted for clarity.

FIGURE 2.16 ROOF LOAD WIDTH (RLW) COMBINATIONS AND ADDITIONS

x y

a b

RLWRLW

RLW + RLWRLW

RLWRLW

2

1 3

A BC

RLW’s for underpurlins are as per Figure 2.15 (b)

A BC

x y

a b

RLW

RLW + RLW

RLW

RLW

V

A B

a

RLW

RLW

+



2.6.5 Area supported The area supported by a member is the contributory area, measured in either the roof or floor plane, that imparts load onto supporting members. The roof area shall be used as an input to Span Tables in the Supplements for strutting beams, combined strutting/hanging beams, combined strutting/counter beams and studs supporting concentrated loads and posts. The floor area shall be used as an input to Span Tables in the Supplements for studs supporting concentrated loads and posts. Typical ‘area supported’ inputs for roofs and floors is illustrated in Figure 2.17.

(a) Typical roof area supported by strutting beam

FIGURE 2.17 AREA SUPPORTED

In the example above, some of the roof load carried by the rafters is supported by an underpurlin that is supported by struts and a strutting beam. The Strutting Beam span table (Table 27) requires a ‘Roof Area Supported (m2)’ input. The strutting beam only supports a single strut so the roof area required to be calculated is the roof area supported by this strut. This is calculated as follows:- Strutted Ridge - The sum of, half the underpurlin spans either side of the strut (half A) (which is the ‘RLW’ of the underpurlin as shown in Figures 2.15), multiplied by the sum of half the rafter spans either side of the underpurlin (half B). Ridge Not Strutted - The sum of, half the underpurlin spans either side of the strut (half A) (which is the ‘RLW’ of the underpurlin as shown in Figure 2.15), multiplied by the sum of half the rafter span from the underpurlin to the top plate and the full span of the rafter from the underpurlin to the ridge (three quarters B).

Strutting Beam Span

Strutting Beam

Underpurlin

Strutting Beam Span

Strutting Beam

Underpurlin

Roof area supported = (1/2)A x (1/2)B(ridge strutted)

Roof area supported = (1/2)A x (3/4)B(ridge not strutted)

B

A

Rafter S

pan

B

A

Rafter S

pan

Stru

t

Stru

t

Stru

t

Stru

t

Stru

t

Stru

t



NOTE: If the post was the central support for a continuous span verandah beam and bearer, the areas supported would be as follows:

(a) Roof area supported = A/2 B

(b) Floor area supported = C/2 D

(b) Typical roof and floor area or supported by post

FIGURE 2.17 AREA SUPPORTED

Joist span C

Bearer Span D

(Post Spacing)

Post

Beam Span

(Post spacing)B

1/2 Beam spanRafte

r span A

1/2 rafte

r span

A2

B2

1/2 Bearer span

1/2 joist spanC2

D2

Roof Area Supported =

2

Bx

2

A

Floor Area Supported =

2

Dx

2

C



2.7 DEFINITIONS — GENERAL 2.7.1 Loadbearing wall A wall that supports roof or floor loads, or both roof and floor loads. 2.7.2 Non-loadbearing walls A non-loadbearing internal wall supports neither roof nor 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. Internal wall frames that do not carry roof loads are considered non-loadbearing. They may still be considered non-loadbearing even though they may incorporate studs that carry ceiling loads and/or studs that support concentrated loads from hanging beams, strutting beams etc. and/or structural bracing. The studs that support concentrated loads in these walls are required to be designed accordingly. See Clause 6.3.2.2.

Note:The non-loadbearing internal wall frame table (Table 6.2) is based on notched studs with an F4 stress grade. For internal non-loadbearing studs over 2700 mm high, 70 x 35 (or say a 90 x 35 instead of 2/90 x 35) studs may be suitable if the studs were not notched and/or a higher stress grade was used. To determine alternate stud sizes to Table 6.2, use the Internal Load-bearing stud tables (Tables 12 & 13). Enter the table for a sheet roof with a 450 rafter/truss spacing. Providing there is a RLW (any RWL > 0 is OK) corresponding to the required stud height and section size it can be used in this non-loadbearing application. EXAMPLE:



A non-loadbearing external wall supports neither roof nor floor loads but may support ceiling loads and act as a bracing wall. A non-loadbearing external wall may support lateral wind loads (e.g. gable or skillion end wall). Non-loadbearing external walls will be required to resist lateral wind loads and therefore must be designed accordingly. This is achieved by choosing a stud size from the external wall stud table (Tables 7 or 8) using the appropriate stud height and stud spacing, and the smallest possible roof load i.e. Sheet roof and the smallest Roof Load Width. 2.7.3 Regulatory authority The authority that is authorized by legal statute as having justification to approve the design and construction of a building, or any part of the building design and construction process. NOTE: In the context of this Standard, the regulatory authority may include local council building surveyors, private building surveyors or other persons nominated by the appropriate State or Territory building legislation as having the legal responsibility for approving the use of structural timber products. 2.7.4 Roofs 2.7.4.1 Coupled roof Pitched roof construction with a roof slope not less than 10º, with ceiling joists and collar ties fixed to opposing common rafter pairs and a ridgeboard at the apex of the roof (see Figure 7.1). A coupled roof system may include some area where it is not possible to fix ceiling joists or collar ties to all rafters; for example, hip ends or parts of a T- or L-shaped house. A coupled roof relies on the triangulation formed by the rafters and ceiling joist to support the roof load. The rafters and ceiling joist MUST be securely fixed (coupled) together at the pitching points to form this triangulation.

If this triangulation cannot be formed or the roof pitch is less than 10º, the roof must be designed as a non-coupled roof i.e. using ridge beams etc..

A coupled roof may incorporate underpurlins, struts, strutting beams etc.

The method of roof construction where the ceiling joists are fixed to the rafters part way up the rafters is NOT covered by AS 1684 and must be individually designed by an engineer.



2.7.4.2 Non-coupled roof A pitched roof that is not a coupled roof and includes cathedral roofs and roofs constructed using ridge and intermediate beams.

2.7.4.3 Pitched roof A roof where members are cut to suit, and which is erected on-site. 2.7.4.4 Trussed roof An engineered roof frame system designed to carry the roof or roof and ceiling, usually without the support of internal walls. AS 1684 does not contain design or installation information for trussed roofs because they are individually engineer designed by truss manufacturers. AS 4440-1997 Installation of nail-plated timber trusses, provides the basic performance requirements and specifications for the bracing, connection and installation of nail -plated timber trusses.

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

Ridge board

Rafters & Ceiling Joist must befixed together at the pitching points

Ceiling joist

Rafter

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

Ceiling joist(Collar Tie)

Rafter

Ridge board

This method of roof construction is not covered by AS1684



2.7.5 Span and spacing 2.7.5.1 General Figure 2.18 illustrates the terms for spacing, span, and single and continuous span. 2.7.5.2 Spacing The centre-to-centre distance between structural members, unless otherwise indicated. 2.7.5.3 Span The face-to-face distance between points capable of giving full support to structural members or assemblies. In particular, 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. 2.7.5.4 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 (see Figures 2.18(c) and 2.18(d)). 2.7.5.5 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 (see Figure 2.18(e)).

Span 1 (2000mm) Span 2 (3930mm)

1/3 (2000mm)

The centre support must be wholly within

the middle third.

Span 2 is not to be greater than twice Span 1.This span is used to determine the size using the continuous span tables.

6000mm

1/3 (2000mm) 1/3 (2000mm)

75mm 75mm 75mm



Joists spacing(centre-l ine to centre-line)

Bearer spacing(centre-l ine to centre-l ine)

Joists span (between internalfaces of support members)

(a) Bearers and joists

Rafter s

pan

Overhang

(b) Rafter

Single span

(c) Two supports

Single span Single span

Saw cut Joint or lap

(d) Joint or sawcut over supports

Continuous span

Continuous span

(e) 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.

FIGURE 2.18 SPACING AND SPAN

Saw cut Joint or lap

Single span Single span



2.7.6 Stress grade The classification of timber to indicate, for the purposes of design, a set of structural design properties in accordance with AS 1720.1. 2.7.7 Stud height The distance from top of bottom plate to underside of top plate or the distance between points of lateral restraint provided to both the breadth and depth of the stud.

2.7.8 Two-storey In any section through the house, construction that includes not more than two levels of timber-framed trafficable floor. Trafficable floors in attics and lofts are included in the number of storeys. In the subfloor of a two-storey construction, the maximum distance from the ground to the underside of the lower floor bearer shall be 1800 mm. NOTE: This requirement does not preclude the application of this Standard to up to a two-storey timber-framed construction supported — (a) by a bearer and joist substructure designed in accordance with this Standard; or (b) by lower levels of timber wall framing or other support systems designed in

accordance with engineering principles and approved by the regulatory authority.

Where full height studs are NOT restrained laterally by a floor or ceiling the stud height is measured between plates.

Where full height studs arelaterally by a floor or

ceiling the stud height is measured between the lateral restraint and the plate.

restrained

Even though this stud is full height, the stud size wil l be c a l c u l a t e d u s i n g t h e greater of A or B

Floor or ceiling framing providing lateral restraint in both directions.

Stu

d h

eig

ht

NOTE: Nogging has been omitted for clarity.

A

B



2.7.9 Rim board A member, at right angles to and fixed to the end of deep joists (including I-joists), that provides restraint to the joists. (see Clause 4.2.2.3.)

Rim board

Although all of the buildings below comply with ‘not more than two levels of timber framed trafficable floor’, if the sub-floor or ground floor was more than 1800 mm off the ground, engineering advice should be sought for the whole structure.

Also see Section 8 - Figure 8.2 (c) Note 1.

1800 mmmax.

1800 mmmax.

>1800 m

m

Engineering

Advice

Required

woodsolutions teaching resource as 1684 section 2...

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