Stringybark, Silvertop

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Silvertop stringybark - named for the grey, fibrous bark extending to the species' upper limbs, which by contrast are whitish and smooth - can attain heights of up to 40 metres. It occurs natively on the coastal fall of tablelands, mainly in northern New South Wales.

The heartwood of this species is a pale brown colour, sometimes with pinkish hues. Its sapwood, up to 50 millimetres in width, is visually indistinct from the true wood. The grain of silvertop stringybark is typically close and straight, with a medium and even texture, relatively free of gum veins.

Silvertop stringybark is a hard timber (rated 2 on a 6-class scale) in relation to both indentation and working with hand tools. It is readily worked by machine, and amenable to the use of standard fittings and fastenings.

In terms of durability, silvertop stringybark is rated as a class 3 hardwood, with an above ground life expectancy of between seven and 15 years, and an in ground life expectancy of between five and 15 years. Silvertop stringybark is not termite-resistant. Sapwood of the species is not susceptible to lyctid borer (powder post beetle) attack, and is readily impregnated with commercially available preservatives.

Applications of silvertop stringybark range from preservative-treated posts, poles, and sleepers to building framework, decking and flooring. It readily accepts paint, stains and polish. Because it glues well with phenolics, Silvertop Stringybark has potential for application in structural plywood and glue-laminated members.

 

Appearance

The heartwood of this species is a pale brown colour, sometimes with pinkish hues. Its sapwood grows to a width of up to 50 millimetres, and is visually indistinct from the species' true wood. Timber grain is typically close and straight, with a medium and even texture relatively free of gum veins.

Common Applications

Common applications range from preservative-treated posts, poles, and sleepers to building framework, decking and flooring. Silvertop stringybark readily accepts paint, stains and polish. Because it glues well with phenolics, timber from this species has a potential for application in structural plywood and glue-laminated members.

Common Form

Sawn

Workability

Silvertop stringybark is not hard to work. It glues well with phenolics so has potential for use in structural plywood and glued-laminated members. It is very similar to blackbutt in general behaviour.

Origin of Timber

NSW

Readily Available

NSW

Availability - Further Information

Silvertop stringybark is relatively common in northern New South Wales.

Availability - Further Information

Native Forest

Shrinkage

Very Low Low Medium High Very High

Tangential :

10.00%

Radial:

6.00%

Unit Movement Tangential:

Unit Movement Radial:

Strength Group

Very High

High

Reasonably High

Medium High

Medium

Reasonably Low

Low

Very Low

Unseasoned:

S1

S2

S3

S4

S5

S6

S7

Seasoned:

SD1

SD2

SD3

SD4

SD5

SD6

SD7

SD8

Stress Grade

Structural
No. 1
Structural
No. 2
Structural
No. 3
Structural
No. 4
Structural
No. 5

Unseasoned:

F27

F17

F14

F11

F8

Seasoned:

F34

F27

F22

F17

F14

Density per Standard

Seasoned:

850kg/m3

Unseasoned:

1050kg/m3

Joint Group

Very High

High

Reasonably High

Medium

Low

Very Low

Unseasoned:

J1

J2

J3

J4

J5

J6

Seasoned:

JD1

JD2

JD3

JD4

JD5

JD6

Colour

  White, yellow, pale straw to light brown Pink to pink brown Light to dark red Brown, chocolate, mottled or streaky
   

Mechanical Properties

Modulus of Rupture - Unseasoned:

87

Modulus of Rupture - Seasoned:

143

Modulus of Elasticity - Unseasoned:

15

Modulus of Elasticity - Seasoned:

18

Maximum Crushing Strength - Unseasoned:

38

Maximum Crushing Strength - Seasoned:

73

Impact - Unseasoned:

17

Impact - Seasoned:

18

Toughness - Unseasoned:

Toughness - Seasoned:

Hardness - Unseasoned:

5.5

Hardness - Seasoned:

8.8

Durability

Low Moderate Reasonably High High
(0 - 5 yrs) (5 - 15 yrs) (15 - 25 yrs) (more than 25 yrs)

In-Ground:

(0 - 7 yrs) (7 - 15 yrs) (15 - 40 yrs) (More than 40 yrs)

Above ground:

(0 - 20 yrs, usually < 5) (21 - 40 yrs) (41 - 64 yrs) (More than 60 yrs)

Marine Borer Resistance:

Lyctid Borer Susceptibility:

Not Susceptible

Lyctid Borer Susceptibility - Other:

Termite Resistance:

Not Resistant

Fire Properties

0 1 2 3 4 5 6 7 8 9 10

EFH Spread-of-Flame Index:

EFH Smoke-Developed Index:

1 - non-combustible 2 - reasonably non-combustible 3 - slightly combustible 4 - combustible

Fire Properties Group
Number:

Group Number - Other:

3 if used on MDF or particleboard ≥12mm; veneer thickness 0.6-0.85mm

Average Specific Extinction Area:

<250

Bushfire Resistance:

BAL 12.5 and 19 – All AS3959 required applications

Portal Frames

Timber portal frames are one of the most favoured structural applications for commercial and industrial buildings whose functions necessitate long spans and open interiors. As a material choice, timber offers designers simplicity, speed and economy in fabrication and erection.

Timber portal frames offer a strong, sound and superior structure. Structural action is achieved through rigid connections between column and rafter at the knees, and between the individual rafter members at the ridge. These rigid joints are generally constructed using nailed plywood gussets and on occasion, with steel gussets.

From material selection to finishing, this application guide provides a comprehensive overview of the process of using timber in the specification, fabrication and erection of portal frame structures.

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