8/3/2019 Estimating Deadloads on Timber Canopies

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???? REF.: TN/19

???? Tel : ???? PAGE:

???? Fax :???? DATE: 31-Jan-2012

???? email: ???? DESIGN: SCH

Member sizes for Collar-Tied Roof Trusses NON-CYCLONIC

Estimate of Deadloads for Standardised Designs

DEADLOAD ESTIMATES

The Basic foundation of limit state strength design is a 5% probability of failure. With respect to deadload, failure has two modes:

1) Deadload below estimate and resistance required not achieved

2) Deadload in excess of estimate and overload results

To account for the variation in dimensions and densities away from the nominal values used in design AS1170:2002 uses partial

load factors.

1) 0.9 for reduction of resisting deadload

2) 1.2 for loading or aggrevating dead weight

These values have supposedly been determined by statistical analysis of the variations in a variety of construction materials used

such that

5% percentile => 5% probability that 0.9G not reached

95% percentile => 5% probability that 1.2G exceeded

The timber framing code AS1684:1999 uses standardised roof masses for production of its supplementary framing tables

it is using:

1) 0.8 for reduction of resisting deadload

2) 1.25 for loading or aggrevating dead weight

from the previous version of AS1170. {The 2006 version of AS1684 may well have adjusted these to the 2002 version of AS1170}

Standard Roof Mass Steel sheet roofing 0.5mm thick and battens 10 kg/m

suggests lower limit 8 kg/m suggests lower limit 9

to AS1684 upper limit 12.5 kg/m to AS1170:2002 upper limit 12

for the current situation roof cladding can change between lightweight polycarbonate sheeting or heavier steel sheeting

also batten spacing can change, along with rafter spacing. Also at initial stage of design frame self weight is unknown.

Cladding weight

Steel Profiles kg/m kPa Polycarb Profiles kg/m kPa

Custom orb 4.3 0.04 ! Corrugated 1.2 0.01 !

4.9 0.05 ! Greca Half Sheet 1.2 0.01 !

Custom Blue Orb 6.1 0.06 Greca Wide Cover 1.2 0.01 !

8 0.08 Wide-Rib 1.2 0.01 !

Integrity 4.7 0.05 Hi-Rib 1.5 0.01 !5.3 0.05 Spantuf 1.5 0.01 !

Integrity 890 4.2 0.04

4.8 0.05 All ! Only

Klip-Lok 406 4.9 0.05 mean 4.077 2.62 kg/m

5.6 0.05 std. dev 1.997 1.72

6.9 0.07 variance 3.989 2.96

Longline 305 3 0.03

Spandek Hi-Ten 4.7 0.05 5% percentile 0.79 -0.21

5.3 0.05 95% percentile 7.36 5.45

Trimdek Hi-ten 4.3 0.04 !

4.9 0.05 !

Batten weight density = 550 kg/m

45 x 70 Area = 3150 mm mass = 1.73 kg/m

spacing = 900 mm Mass = 1.93 kg/m 0.02 mean 1.684 5% percentile 1.12

spacing = 1200 mm Mass = 1.44 kg/m 0.01 std. dev 0.340 95% percentile 2.24

spacing of battens varies depending on cladding internal and end spans and the over all span of the canopy

Frame weight (Rafters) density = 550 kg/m spacing = 1200 mm

Area mass

mm kg/m kg/m kPa mean 2.793 kg/m

90 x 35 3150 1.73 1.44 0.01 std. dev 0.925

120x35 4200 2.31 1.93 0.02 5% percentile 1.27

120x45 5400 2.97 2.48 0.02 95% percentile 4.31

140x45 6300 3.47 2.89 0.03

190x35 6650 3.66 3.05 0.03

190x45 8550 4.70 3.92 0.04

240x35 8400 4.62 3.85 0.04

Total Frame Weight Lower Limit 3.19 kg/m Upper Limit 13.92 kg/m 0.14adjusted to allow for partial load factors 0.03 kPa 0.11 kPa

Therefore standardised roof mass mostly over estimates resistance and slightly under estimates loading. (eg.0.11>0.1kPa)

Therefore produce additional design curves for alternative deadloading and assess variation to member sizes.

schGableCanopyTimber.xls DeadLoading