AREA OF ELEVATION - RACKING FORCES - AS 4055-2012 Wind loads for housing.pdf

SECTION 5 RACKING FORCES

5.2 AREA OF ELEVATION

Area of elevation appropriate for calculation of racking forces shall be as shown in Figures 5.1 to 5.3.

The wind direction used shall be that resulting in the greatest load for the length and width of the building, respectively. As wind can blow from any direction, the elevation used shall be that for the worst direction. In the case of a single-storey house with a gable at one end and a hip at the other, the gable end facing the wind will result in a greater amount of load

W i n d d i r e c t i o n 1

W i n d d i r e c t i o n 2 G a b l e e n d

H i p e n d

A r e a o f e l eva t i o n

F l o o r l eve l A r e a o f e l eva t i o n ( g a b l e e n d s) A r e a o f

e l eva t i o n

F l o o r l eve l (a ) Pl a n

( b) W i n d d i r e c t i o n 1

( b) W i n d d i r e c t i o n 2 NOTES:

1 h0 = half the height of the wall (half of the floor to ceiling height).

2 For lower storey of two-storey section ho = half the height of the lower storey (i.e., lower storey floor to lower storey ceiling).

3 The area of elevation of the triangular portion of eaves overhang up to 1000 mm wide may be ignored in the determination of area of elevation.

FIGURE 5.1 DETERMINING AREA OF ELEVATION FOR A SINGLE-STOREY BUILDING

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(a ) Pl a n

( b) W i n d d i r e c t i o n 1

W i n d d i r e c t i o n 1

W i n d d i r e c t i o n 2

G a b l e e n d

H i p e n d

F l o o r l eve l

C e i l i n g l eve l F l o o r l eve l

U p p e r s to r ey o f t wo - s to r ey s e c t i o n

S i n g l e - s to r ey s e c t i o n A r e a o f e l eva t i o n ( g a b l e e n d )

L owe r s to r ey o f t wo - s to r ey s e c t i o n A r e a o f

e l eva t i o n

A r e a o f e l eva t i o n ( g a b l e e n d )

A r e a o f e l eva t i o n A r e a o f e l eva t i o n

L owe r s to r ey o f t wo - s to r ey s e c t i o n U p p e r s to r ey o f t wo - s to r ey s e c t i o n

C e i l i n g l eve l U p p e r f l o o r l eve l F l o o r l eve l

W i n d d i r e c t i o n 2 W i n d d i r e c t i o n 3 G a b l e e n d H i p e n d

W i n d d i r e c t i o n 1

F l o o r A r e a of

e l eva t i o n

H0 h0

A r e a of e l eva t i o n F l o o r

F l o o r A r e a of e l eva t i o n

(a ) Pl a n

( b) W i n d d i r e c t i o n 1

(c) W i n d d i r e c t i o n 2—H i p e n d (d ) W i n d d i r e c t i o n 3—G a b l e e n d I n t h e s u bf l o o r of a t wo - s to r ey c o n s t r u c t i o n , t h e m a x i m u m d i s t a n c e (H0) f r o m t h e g r o u n d to t h e u n d e r s i d e of t h e b e a r e r i n t h e l owe r f l o o r s h a l l b e 18 0 0 m m .

FIGURE 5.3 DETERMINING AREA OF ELEVATION FOR SUBFLOORS NOTES:

1 h0 = half the height from the ground to the lower-storey floor.

2 For wind direction 2, the pressure on the gable end is determined from Table 5.1 and the pressure on the hip section of the elevation is determined from Tables 5.2 to 5.13. The total of racking forces is the sum of the forces calculated for each section.

3 The area of elevation of the triangular portion of eaves overhang up to 1000 mm wide may be ignored in the determination of area of elevation.

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TABLE 5.1

VERTICAL SURFACES (FLAT WALLS, GABLE ENDS AND SKILLION ENDS)—

PRESSURE ON AREA OF ELEVATION

W i n d d i r e c t i o n W i n d d i r e c t i o n

W i n d d i r e c t i o n

Wind class Pressure kPa

N1 0.66 N2 0.92 N3 1.44 N4 2.14 N5 3.16 N6 4.26 C1 1.44 C2 2.14 C3 3.16 C4 4.26

TABLE 5.2

HIP ROOFS AND SIDE WIND ON GABLE ROOFS—PRESSURE (kPa) ON AREA OF ELEVATION—SINGLE STOREY OR UPPER FLOOR OF TWO STOREYS

Single storey or upper floor of two storeys, 2.4 m storey, 0.3 m floor Width (m) Roof pitch (degrees)

0 5 10 15 20 25 30 35

W i n d d i r e c t i o n W i n d d i r e c t i o n

W W

N1: Wind on side

4 0.61 0.53 0.48 0.45 0.49 0.56 0.56 0.57 5 0.61 0.52 0.46 0.44 0.49 0.56 0.55 0.57 6 0.61 0.50 0.43 0.44 0.50 0.56 0.55 0.57 7 0.61 0.49 0.41 0.44 0.50 0.56 0.55 0.58 8 0.61 0.47 0.39 0.44 0.51 0.56 0.55 0.58 9 0.61 0.46 0.37 0.44 0.51 0.56 0.55 0.58 10 0.61 0.45 0.35 0.43 0.51 0.56 0.55 0.58 11 0.61 0.44 0.34 0.43 0.51 0.55 0.55 0.58 12 0.61 0.42 0.32 0.42 0.50 0.55 0.54 0.58 13 0.61 0.41 0.31 0.41 0.50 0.55 0.54 0.58 14 0.61 0.40 0.30 0.41 0.50 0.54 0.54 0.58 15 0.61 0.39 0.29 0.40 0.49 0.54 0.54 0.58 16 0.61 0.39 0.28 0.40 0.49 0.54 0.53 0.57

W i n d d i r e c t i o n W i n d d i r e c t i on

W W

N1: Wind on end

4 0.67 0.62 0.59 0.56 0.60 0.57 0.59 0.60 5 0.67 0.61 0.57 0.55 0.59 0.56 0.58 0.60 6 0.67 0.60 0.55 0.54 0.59 0.56 0.58 0.60 7 0.67 0.59 0.53 0.54 0.59 0.56 0.58 0.60 8 0.67 0.58 0.52 0.54 0.59 0.56 0.58 0.60 9 0.67 0.57 0.50 0.53 0.59 0.56 0.58 0.60 10 0.67 0.56 0.49 0.53 0.58 0.56 0.57 0.60 11 0.67 0.55 0.47 0.52 0.58 0.56 0.57 0.60 12 0.67 0.55 0.46 0.51 0.58 0.56 0.57 0.60 13 0.67 0.54 0.45 0.50 0.57 0.56 0.56 0.59 14 0.67 0.53 0.44 0.50 0.57 0.56 0.56 0.59 15 0.67 0.52 0.43 0.49 0.57 0.56 0.56 0.59 16 0.67 0.52 0.42 0.48 0.56 0.56 0.56 0.59

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TABLE 5.3

HIP ROOFS AND SIDE WIND ON GABLE ROOFS—PRESSURE (kPa) ON AREA OF ELEVATION—LOWER STOREY OF TWO STOREYS

Lower storey of two storeys, 2.4 m storey, 0.3 m floor Width (m) Roof pitch (degrees)

0 5 10 15 20 25 30 35

Wind direction Wind direction

W W

N1: Wind on side

4 0.61 0.58 0.56 0.54 0.54 0.60 0.62 0.61 5 0.61 0.58 0.55 0.53 0.53 0.59 0.61 0.60 6 0.61 0.57 0.54 0.52 0.52 0.59 0.60 0.59 7 0.61 0.57 0.53 0.51 0.52 0.59 0.59 0.59 8 0.61 0.56 0.53 0.50 0.52 0.58 0.58 0.59 9 0.61 0.55 0.52 0.49 0.52 0.58 0.58 0.59 10 0.61 0.55 0.51 0.48 0.52 0.58 0.57 0.59 11 0.61 0.54 0.50 0.48 0.52 0.58 0.57 0.59 12 0.61 0.54 0.49 0.48 0.52 0.58 0.57 0.59 13 0.61 0.53 0.48 0.48 0.52 0.58 0.57 0.59 14 0.61 0.53 0.47 0.48 0.52 0.58 0.57 0.59 15 0.61 0.52 0.46 0.48 0.53 0.58 0.57 0.59 16 0.61 0.52 0.45 0.48 0.53 0.58 0.57 0.59

Wind direction W

N1: Wind on end

4 0.67 0.65 0.64 0.63 0.62 0.63 0.64 0.63 5 0.67 0.65 0.63 0.62 0.61 0.62 0.63 0.63 6 0.67 0.64 0.63 0.61 0.61 0.62 0.63 0.62 7 0.67 0.64 0.62 0.60 0.61 0.62 0.62 0.62 8 0.67 0.64 0.62 0.60 0.61 0.62 0.62 0.62

TABLE 5.4

HIP ROOFS AND SIDE WIND ON GABLE ROOFS—PRESSURE (kPa) ON AREA OF ELEVATION—SINGLE STOREY OR UPPER FLOOR OF TWO STOREYS

Single storey or upper floor of two storeys, 2.4 m storey, 0.3 m floor Width (m) Roof pitch (degrees)

0 5 10 15 20 25 30 35

W i n d d i r e c t i o n W i n d d i r e c t i o n

W W

N2: Wind on side

4 0.84 0.74 0.67 0.61 0.61 0.72 0.77 0.76 5 0.84 0.71 0.64 0.57 0.58 0.69 0.75 0.74 6 0.84 0.69 0.61 0.55 0.59 0.70 0.74 0.74 7 0.84 0.67 0.58 0.53 0.59 0.70 0.73 0.74 8 0.84 0.65 0.56 0.51 0.60 0.71 0.72 0.75 9 0.84 0.64 0.54 0.49 0.61 0.71 0.71 0.75 10 0.84 0.62 0.52 0.48 0.61 0.72 0.70 0.75 11 0.84 0.60 0.50 0.48 0.62 0.72 0.71 0.75 12 0.84 0.59 0.47 0.49 0.63 0.72 0.71 0.76 13 0.84 0.57 0.45 0.49 0.63 0.73 0.71 0.77 14 0.84 0.56 0.43 0.50 0.64 0.73 0.72 0.77 15 0.84 0.55 0.42 0.50 0.65 0.73 0.72 0.77 16 0.84 0.53 0.40 0.51 0.65 0.73 0.72 0.78

W i n d d i r e c t i o n W i n d d i r e c t i on

W W

N2: Wind on end

4 0.92 0.86 0.81 0.77 0.76 0.79 0.82 0.81 5 0.92 0.84 0.79 0.74 0.73 0.77 0.81 0.79 6 0.92 0.83 0.77 0.72 0.73 0.77 0.79 0.79 7 0.92 0.82 0.75 0.70 0.73 0.77 0.78 0.79 8 0.92 0.80 0.73 0.68 0.72 0.77 0.77 0.79 9 0.92 0.79 0.71 0.66 0.72 0.77 0.76 0.79 10 0.92 0.78 0.69 0.65 0.72 0.77 0.75 0.78 11 0.92 0.77 0.68 0.64 0.72 0.77 0.75 0.79 12 0.92 0.76 0.66 0.64 0.72 0.77 0.75 0.79 13 0.92 0.75 0.64 0.64 0.73 0.77 0.75 0.79 14 0.92 0.73 0.62 0.64 0.73 0.77 0.76 0.79 15 0.92 0.72 0.60 0.64 0.73 0.77 0.76 0.80 16 0.92 0.71 0.59 0.64 0.73 0.77 0.76 0.80

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TABLE 5.5

HIP ROOFS AND SIDE WIND ON GABLE ROOFS—PRESSURE (kPa) ON AREA OF ELEVATION—LOWER STOREY OF TWO STOREYS

Lower storey of two storeys, 2.4 m storey, 0.3 m floor Width

(m)

Roof pitch (degrees)

0 5 10 15 20 25 30 35

Wind direction Wind direction

W W

N2: Wind on side

4 0.84 0.81 0.78 0.75 0.75 0.83 0.85 0.84 5 0.84 0.80 0.77 0.73 0.73 0.82 0.84 0.83 6 0.84 0.79 0.75 0.72 0.73 0.81 0.83 0.82 7 0.84 0.78 0.74 0.70 0.72 0.81 0.82 0.82 8 0.84 0.78 0.73 0.69 0.72 0.81 0.81 0.82 9 0.84 0.77 0.71 0.68 0.72 0.81 0.80 0.81 10 0.84 0.76 0.70 0.67 0.72 0.81 0.79 0.81 11 0.84 0.75 0.69 0.66 0.72 0.80 0.79 0.81 12 0.84 0.74 0.68 0.66 0.72 0.80 0.79 0.81 13 0.84 0.74 0.66 0.66 0.72 0.80 0.79 0.82 14 0.84 0.73 0.65 0.66 0.73 0.80 0.79 0.82 15 0.84 0.72 0.64 0.66 0.73 0.80 0.79 0.82 16 0.84 0.72 0.63 0.66 0.73 0.80 0.79 0.82

Wind direction W

N2: Wind on end

4 0.92 0.90 0.89 0.87 0.86 0.87 0.88 0.87 5 0.92 0.90 0.88 0.85 0.85 0.86 0.87 0.87 6 0.92 0.89 0.87 0.84 0.85 0.86 0.87 0.86 7 0.92 0.89 0.86 0.84 0.84 0.86 0.86 0.86 8 0.92 0.88 0.85 0.83 0.84 0.85 0.85 0.86

TABLE 5.6

HIP ROOFS AND SIDE WIND ON GABLE ROOFS—

PRESSURE (kPa) ON AREA OF ELEVATION—

SINGLE STOREY OR UPPER FLOOR OF TWO STOREYS

Single storey or upper floor of two storeys, 2.4 m storey, 0.3 m floor Width (m) Roof pitch (degrees)

0 5 10 15 20 25 30 35

W i n d d i r e c t i o n W i n d d i r e c t i o n

W W

N3, C1: Wind on side

4 1.30 1.20 1.00 0.95 0.96 1.10 1.20 1.20 5 1.30 1.10 1.00 0.89 0.91 1.10 1.20 1.20 6 1.30 1.10 0.95 0.85 0.91 1.10 1.20 1.20 7 1.30 1.10 0.91 0.82 0.93 1.10 1.10 1.20 8 1.30 1.00 0.88 0.79 0.94 1.10 1.10 1.20 9 1.30 0.99 0.84 0.77 0.95 1.10 1.10 1.20 10 1.30 0.97 0.81 0.75 0.95 1.10 1.10 1.20 11 1.30 0.94 0.78 0.75 0.97 1.10 1.10 1.20 12 1.30 0.92 0.74 0.76 0.98 1.10 1.10 1.20 13 1.30 0.90 0.71 0.77 0.99 1.10 1.10 1.20 14 1.30 0.87 0.68 0.78 1.00 1.10 1.10 1.20 15 1.30 0.85 0.65 0.79 1.00 1.10 1.10 1.20 16 1.30 0.83 0.62 0.79 1.00 1.10 1.10 1.20

W i n d d i r e c t i o n W i n d d i r e c t i on

W W

N3, C1: Wind on end

4 1.40 1.30 1.30 1.20 1.20 1.20 1.30 1.30 5 1.40 1.30 1.20 1.20 1.10 1.20 1.30 1.20 6 1.40 1.30 1.20 1.10 1.10 1.20 1.20 1.20 7 1.40 1.30 1.20 1.10 1.10 1.20 1.20 1.20 8 1.40 1.30 1.10 1.10 1.10 1.20 1.20 1.20 9 1.40 1.20 1.10 1.00 1.10 1.20 1.20 1.20 10 1.40 1.20 1.10 1.00 1.10 1.20 1.20 1.20 11 1.40 1.20 1.10 1.00 1.10 1.20 1.20 1.20 12 1.40 1.20 1.00 1.00 1.10 1.20 1.20 1.20 13 1.40 1.20 1.00 1.00 1.10 1.20 1.20 1.20 14 1.40 1.10 0.97 1.00 1.10 1.20 1.20 1.20 15 1.40 1.10 0.94 1.00 1.10 1.20 1.20 1.20 16 1.40 1.10 0.92 1.00 1.10 1.20 1.20 1.20

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TABLE 5.7

HIP ROOFS AND SIDE WIND ON GABLE ROOFS—

PRESSURE (kPa) ON AREA OF ELEVATION—

LOWER STOREY OF TWO STOREYS

Lower storey of two storeys, 2.4 m storey, 0.3 m floor Width (m) Roof pitch (degrees)

0 5 10 15 20 25 30 35

Wind direction Wind direction

W W

N3, C1: Wind on side

4 1.30 1.30 1.20 1.20 1.20 1.30 1.30 1.30 5 1.30 1.20 1.20 1.10 1.10 1.30 1.30 1.30 6 1.30 1.20 1.20 1.10 1.10 1.30 1.30 1.30 7 1.30 1.20 1.20 1.10 1.10 1.30 1.30 1.30 8 1.30 1.20 1.10 1.10 1.10 1.30 1.30 1.30 9 1.30 1.20 1.10 1.10 1.10 1.30 1.20 1.30 10 1.30 1.20 1.10 1.00 1.10 1.30 1.20 1.30 11 1.30 1.20 1.10 1.00 1.10 1.30 1.20 1.30 12 1.30 1.20 1.10 1.00 1.10 1.30 1.20 1.30 13 1.30 1.20 1.00 1.00 1.10 1.30 1.20 1.30 14 1.30 1.10 1.00 1.00 1.10 1.30 1.20 1.30 15 1.30 1.10 1.00 1.00 1.10 1.20 1.20 1.30 16 1.30 1.10 0.98 1.00 1.10 1.20 1.20 1.30

Wind direction W

N3, C1: Wind on end

4 1.40 1.40 1.40 1.40 1.30 1.40 1.40 1.40 5 1.40 1.40 1.40 1.30 1.30 1.30 1.40 1.40 6 1.40 1.40 1.40 1.30 1.30 1.30 1.40 1.30 7 1.40 1.40 1.30 1.30 1.30 1.30 1.30 1.30

TABLE 5.8

HIP ROOFS AND SIDE WIND ON GABLE ROOFS—PRESSURE (kPa) ON AREA OF ELEVATION—SINGLE STOREY OR UPPER FLOOR OF TWO STOREYS

Single storey or upper floor of two storeys, 2.4 m storey, 0.3 m floor Width (m) Roof pitch (degrees)

0 5 10 15 20 25 30 35

W i n d d i r e c t i o n W i n d d i r e c t i o n

W W

N4, C2: Wind on side

4 2.00 1.70 1.60 1.40 1.40 1.70 1.80 1.80 5 2.00 1.70 1.50 1.30 1.30 1.60 1.80 1.70 6 2.00 1.60 1.40 1.30 1.40 1.60 1.70 1.70 7 2.00 1.60 1.40 1.20 1.40 1.60 1.70 1.70 8 2.00 1.50 1.30 1.20 1.40 1.60 1.70 1.70 9 2.00 1.50 1.30 1.10 1.40 1.70 1.70 1.70 10 2.00 1.40 1.20 1.10 1.40 1.70 1.60 1.70 11 2.00 1.40 1.20 1.10 1.40 1.70 1.60 1.80 12 2.00 1.40 1.10 1.10 1.50 1.70 1.70 1.80 13 2.00 1.30 1.10 1.10 1.50 1.70 1.70 1.80 14 2.00 1.30 1.00 1.20 1.50 1.70 1.70 1.80 15 2.00 1.30 0.97 1.20 1.50 1.70 1.70 1.80 16 2.00 1.20 0.93 1.20 1.50 1.70 1.70 1.80

W i n d d i r e c t i o n W i n d d i r e c t i on

W W

N4, C2: Wind on end

4 2.10 2.00 1.90 1.80 1.80 1.80 1.90 1.90 5 2.10 2.00 1.80 1.70 1.70 1.80 1.90 1.80 6 2.10 1.90 1.80 1.70 1.70 1.80 1.80 1.80 7 2.10 1.90 1.70 1.60 1.70 1.80 1.80 1.80 8 2.10 1.90 1.70 1.60 1.70 1.80 1.80 1.80 9 2.10 1.80 1.70 1.50 1.70 1.80 1.80 1.80 10 2.10 1.80 1.60 1.50 1.70 1.80 1.80 1.80 11 2.10 1.80 1.60 1.50 1.70 1.80 1.80 1.80 12 2.10 1.80 1.50 1.50 1.70 1.80 1.80 1.80 13 2.10 1.70 1.50 1.50 1.70 1.80 1.80 1.80 14 2.10 1.70 1.40 1.50 1.70 1.80 1.80 1.80 15 2.10 1.70 1.40 1.50 1.70 1.80 1.80 1.90 16 2.10 1.70 1.40 1.50 1.70 1.80 1.80 1.90

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TABLE 5.9

HIP ROOFS AND SIDE WIND ON GABLE ROOFS—

PRESSURE (kPa) ON AREA OF ELEVATION—

LOWER STOREY OF TWO STOREYS

Lower storey of two storeys, 2.4 m storey, 0.3 m floor Width (m) Roof pitch (degrees)

0 5 10 15 20 25 30 35

Wind direction Wind direction

W W

N4, C2: Wind on side

4 2.00 1.90 1.80 1.70 1.70 1.90 2.00 2.00 5 2.00 1.90 1.80 1.70 1.70 1.90 2.00 1.90 6 2.00 1.80 1.80 1.70 1.70 1.90 1.90 1.90 7 2.00 1.80 1.70 1.60 1.70 1.90 1.90 1.90 8 2.00 1.80 1.70 1.60 1.70 1.90 1.90 1.90 9 2.00 1.80 1.70 1.60 1.70 1.90 1.90 1.90 10 2.00 1.80 1.60 1.60 1.70 1.90 1.80 1.90 11 2.00 1.70 1.60 1.50 1.70 1.90 1.80 1.90 12 2.00 1.70 1.60 1.50 1.70 1.90 1.80 1.90 13 2.00 1.70 1.50 1.50 1.70 1.90 1.80 1.90 14 2.00 1.70 1.50 1.50 1.70 1.90 1.80 1.90 15 2.00 1.70 1.50 1.50 1.70 1.90 1.80 1.90 16 2.00 1.70 1.50 1.50 1.70 1.90 1.80 1.90

Wind direction W

N4, C2: Wind on end

4 2.10 2.10 2.10 2.00 2.00 2.00 2.10 2.00 5 2.10 2.10 2.00 2.00 2.00 2.00 2.00 2.00 6 2.10 2.10 2.00 2.00 2.00 2.00 2.00 2.00 7 2.10 2.10 2.00 1.90 2.00 2.00 2.00 2.00

TABLE 5.10

HIP ROOFS AND SIDE WIND ON GABLE ROOFS—

PRESSURE (kPa) ON AREA OF ELEVATION—

SINGLE STOREY OR UPPER FLOOR OF TWO STOREYS

Single storey or upper floor of two storeys, 2.4 m storey, 0.3 m floor Width (m) Roof pitch (degrees)

0 5 10 15 20 25 30 35

W i n d d i r e c t i o n W i n d d i r e c t i o n

W W

N5, C3: Wind on side

4 2.90 2.50 2.30 2.10 2.10 2.50 2.60 2.60 5 2.90 2.40 2.20 1.90 2.00 2.40 2.60 2.50 6 2.90 2.40 2.10 1.90 2.00 2.40 2.50 2.50 7 2.90 2.30 2.00 1.80 2.00 2.40 2.50 2.50 8 2.90 2.20 1.90 1.70 2.10 2.40 2.50 2.60 9 2.90 2.20 1.80 1.70 2.10 2.40 2.40 2.60 10 2.90 2.10 1.80 1.60 2.10 2.50 2.40 2.60 11 2.90 2.10 1.70 1.70 2.10 2.50 2.40 2.60 12 2.90 2.00 1.60 1.70 2.10 2.50 2.40 2.60 13 2.90 2.00 1.60 1.70 2.20 2.50 2.40 2.60 14 2.90 1.90 1.50 1.70 2.20 2.50 2.50 2.60 15 2.90 1.90 1.40 1.70 2.20 2.50 2.50 2.60 16 2.90 1.80 1.40 1.70 2.20 2.50 2.50 2.70

W i n d d i r e c t i o n W i n d d i r e c t i on

W W

N5, C3: Wind on end

4 3.20 2.90 2.80 2.60 2.60 2.70 2.80 2.80 5 3.20 2.90 2.70 2.50 2.50 2.60 2.80 2.70 6 3.20 2.80 2.60 2.40 2.50 2.60 2.70 2.70 7 3.20 2.80 2.60 2.40 2.50 2.60 2.70 2.70 8 3.20 2.80 2.50 2.30 2.50 2.60 2.60 2.70 9 3.20 2.70 2.40 2.30 2.50 2.60 2.60 2.70 10 3.20 2.70 2.40 2.20 2.50 2.60 2.60 2.70 11 3.20 2.60 2.30 2.20 2.50 2.60 2.60 2.70 12 3.20 2.60 2.20 2.20 2.50 2.60 2.60 2.70 13 3.20 2.50 2.20 2.20 2.50 2.60 2.60 2.70 14 3.20 2.50 2.10 2.20 2.50 2.60 2.60 2.70 15 3.20 2.50 2.10 2.20 2.50 2.60 2.60 2.70 16 3.20 2.40 2.00 2.20 2.50 2.60 2.60 2.70

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TABLE 5.11

HIP ROOFS AND SIDE WIND ON GABLE ROOFS—PRESSURE (kPa) ON AREA OF ELEVATION—LOWER STOREY OF TWO STOREYS

Lower storey of two storeys, 2.4 m storey, 0.3 m floor Width (m) Roof pitch (degrees)

0 5 10 15 20 25 30 35

Wind direction Wind direction

W W

N5, C3: Wind on side

4 2.90 2.80 2.70 2.60 2.60 2.80 2.90 2.90 5 2.90 2.70 2.60 2.50 2.50 2.80 2.90 2.80 6 2.90 2.70 2.60 2.50 2.50 2.80 2.80 2.80 7 2.90 2.70 2.50 2.40 2.50 2.80 2.80 2.80 8 2.90 2.70 2.50 2.40 2.50 2.80 2.80 2.80 9 2.90 2.60 2.40 2.30 2.50 2.80 2.70 2.80 10 2.90 2.60 2.40 2.30 2.50 2.80 2.70 2.80 11 2.90 2.60 2.40 2.30 2.50 2.80 2.70 2.80 12 2.90 2.50 2.30 2.30 2.50 2.70 2.70 2.80 13 2.90 2.50 2.30 2.30 2.50 2.70 2.70 2.80 14 2.90 2.50 2.20 2.30 2.50 2.70 2.70 2.80 15 2.90 2.50 2.20 2.30 2.50 2.70 2.70 2.80 16 2.90 2.50 2.10 2.30 2.50 2.70 2.70 2.80

Wind direction W

N5, C3: Wind on end

4 3.20 3.10 3.00 3.00 3.00 3.00 3.00 3.00 5 3.20 3.10 3.00 2.90 2.90 2.90 3.00 3.00 6 3.20 3.10 3.00 2.90 2.90 2.90 3.00 2.90 7 3.20 3.00 2.90 2.90 2.90 2.90 2.90 2.90 8 3.20 3.00 2.90 2.80 2.90 2.90 2.90 2.90

TABLE 5.12

HIP ROOFS AND SIDE WIND ON GABLE ROOFS—

PRESSURE (kPa) ON AREA OF ELEVATION—

SINGLE STOREY OR UPPER FLOOR OF TWO STOREYS

Single storey or upper floor of two storeys, 2.4 m storey, 0.3 m floor Width (m) Roof pitch (degrees)

0 5 10 15 20 25 30 35

W i n d d i r e c t i o n W i n d d i r e c t i o n

W W

N6, C4: Wind on side

4 3.92 3.38 3.11 2.84 2.84 3.38 3.51 3.51 5 3.92 3.24 2.97 2.57 2.70 3.24 3.51 3.38 6 3.92 3.24 2.84 2.57 2.70 3.24 3.38 3.38 7 3.92 3.11 2.70 2.43 2.70 3.24 3.38 3.38 8 3.92 2.97 2.57 2.30 2.84 3.24 3.38 3.51 9 3.92 2.97 2.43 2.30 2.84 3.24 3.24 3.51 10 3.92 2.84 2.43 2.16 2.84 3.38 3.24 3.51 11 3.92 2.84 2.30 2.30 2.84 3.38 3.24 3.51 12 3.92 2.70 2.16 2.30 2.84 3.38 3.24 3.51 13 3.92 2.70 2.16 2.30 2.97 3.38 3.24 3.51 14 3.92 2.57 2.03 2.30 2.97 3.38 3.38 3.51 15 3.92 2.57 1.89 2.30 2.97 3.38 3.38 3.51 16 3.92 2.43 1.89 2.30 2.97 3.38 3.38 3.65

W i n d d i r e c t i o n W i n d d i r e c t i on

W W

N6, C4: Wind on end

4 4.32 3.92 3.78 3.51 3.51 3.65 3.78 3.78 5 4.32 3.92 3.65 3.38 3.38 3.51 3.78 3.65 6 4.32 3.78 3.51 3.24 3.38 3.51 3.65 3.65 7 4.32 3.78 3.51 3.24 3.38 3.51 3.65 3.65 8 4.32 3.78 3.38 3.11 3.38 3.51 3.51 3.65 9 4.32 3.65 3.24 3.11 3.38 3.51 3.51 3.65 10 4.32 3.65 3.24 2.97 3.38 3.51 3.51 3.65 11 4.32 3.51 3.11 2.97 3.38 3.51 3.51 3.65 12 4.32 3.51 2.97 2.97 3.38 3.51 3.51 3.65 13 4.32 3.38 2.97 2.97 3.38 3.51 3.51 3.65 14 4.32 3.38 2.84 2.97 3.38 3.51 3.51 3.65 15 4.32 3.38 2.84 2.97 3.38 3.51 3.51 3.65 16 4.32 3.24 2.70 2.97 3.38 3.51 3.51 3.65

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TABLE 5.13

HIP ROOFS AND SIDE WIND ON GABLE ROOFS—

PRESSURE (kPa) ON AREA OF ELEVATION—

LOWER STOREY OF TWO STOREYS

Lower storey of two storeys, 2.4 m storey, 0.3 m floor Width (m) Roof pitch (degrees)

0 5 10 15 20 25 30 35

Wind direction Wind direction

W W

N6, C4: Wind on side

4 3.92 3.78 3.65 3.51 3.51 3.78 3.92 3.92 5 3.92 3.65 3.51 3.38 3.38 3.78 3.92 3.78 6 3.92 3.65 3.51 3.38 3.38 3.78 3.78 3.78 7 3.92 3.65 3.38 3.24 3.38 3.78 3.78 3.78 8 3.92 3.65 3.38 3.24 3.38 3.78 3.78 3.78 9 3.92 3.51 3.24 3.11 3.38 3.78 3.65 3.78 10 3.92 3.51 3.24 3.11 3.38 3.78 3.65 3.78 11 3.92 3.51 3.24 3.11 3.38 3.78 3.65 3.78 12 3.92 3.38 3.11 3.11 3.38 3.65 3.65 3.78 13 3.92 3.38 3.11 3.11 3.38 3.65 3.65 3.78 14 3.92 3.38 2.97 3.11 3.38 3.65 3.65 3.78 15 3.92 3.38 2.97 3.11 3.38 3.65 3.65 3.78 16 3.92 3.38 2.84 3.11 3.38 3.65 3.65 3.78

Wind direction W

N6, C4: Wind on end

4 4.32 4.19 4.05 4.05 4.05 4.05 4.05 4.05 5 4.32 4.19 4.05 3.92 3.92 3.92 4.05 4.05 6 4.32 4.19 4.05 3.92 3.92 3.92 4.05 3.92 7 4.32 4.05 3.92 3.92 3.92 3.92 3.92 3.92

APPENDIX A COMMENTARY

(Informative) A1 COMMENTARY ON SCOPE AND GENERAL A1.1 General

This Standard has been derived for houses as a group or large numbers of buildings. In general, the level of reliability for the group is similar to that found by applying AS/NZS 1170.2. However, it is recognized that a correct application of this Standard may lead to some houses with more conservative design loads, and others with less conservative design loads.

It is important to categorize each building on a case-by-case basis. Each site should be assessed individually for its wind classification. Each building must be assessed for compliance with geometry and for evaluation of pressures.

A1.2 Comment on Clause 1.3—Geometric Limits

The geometric limits presented in Clause 1.3 have been provided to enable some simplifications to the AS/NZS 1170.2 methods for the most common geometries of housing.

It is intended that 16 m width limit be applied to the width of the tallest section of the house. For example, in many cases the various sections of a house (that is the basic rectangular box shapes) may be displaced horizontally with respect to each other. This could make the overall floor plan dimension greater than the 16 m limit even though none of the sections of roof might be wider than 16 m.

Such a house should be within the limits provided that none of the roof sections parallel to the wind direction being considered are greater than 16 m (neglecting the width of eaves).

A2 COMMENT ON TABLE 2.1—WIND CLASSIFICATION

An approximate 50% increase in wind pressures occurs from one class to the next higher one, that is, N2 to N3, N3 to N4, etc.

Once a particular building site has been classified using the methods set out in Section 2, the ultimate wind speed for that class represents the design wind speed for the house and includes the effects of—

(a) the importance level which is set by the NCC (the design wind loading level associated with housing);

(b) directionality (the likelihood of wind occurring at its maximum from the direction for which the house is most vulnerable in terms of the pressures on the envelope);

(d) terrain roughness (sizes of the obstructions in the wider area around the building site such as water, grass, open space and size of buildings);

(e) topography (the position of the site on hills or in valleys); and

(f) shielding (the effect of specific buildings and other obstructions near to the proposed building).

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A3 DERIVATION OF TABLE 2.2—WIND CLASSIFICATION A3.1 Wind classification

In determining the application of the N and C classes to the selected site criteria that are given in Table 2.2, a number of simplifications of the methods in AS/NZS 1170.2 were made. The classifications were derived from a range of design scenarios that were evaluated using AS/NZS 1170.2. The following criteria were selected:

(a) Annual probability of exceedance has been taken as 1/500.

(b) A 0.95 factor on wind speed was allowed to account for the variation of orientation of houses within suburbs and groups of suburbs and the fact that the peak wind gust will only come from a single direction. There will be few for which this direction is the critical one with respect to terrain, topography and the house orientation.

(d) Average roof height has been taken as 6.5 m (selected as not the worst case but covering the majority of average housing being constructed within the limitations given in Figure 1.1).

(e) The terrain/height multiplier (M6.5,cat) has been derived from AS/NZS 1170.2 with h (average roof height) taken as 6.5 m (see Table A1).

(f) Topographic multiplier (Mt) has been derived from the hill shape multiplier defined in AS/NZS 1170.2 (see Table A2). The values chosen for T1 to T5 represent the average of the ranges for each class (T0 is taken as 1.0 to represent housing on flat or nearly flat topography). For the top third, the class changes for slopes greater than 30 m high. A column has also been included for hill heights of less than 10 m to facilitate correct classification of topography on small hills (with a height the same order as the height of houses). The separation zone at the crest has not been included, but for escarpments only, a zone immediately over the crest is included.

Shielding multiplier (M_s) has been derived from AS/NZS 1170.2 (see Table A3).

TABLE A1

TERRAIN CATEGORY MULTIPLIER (M6.5,cat) AT HEIGHT 6.5 m

Region

Terrain category multiplier (M6.5,cat) Terrain

Category 1

Terrain Category 1.5

Terrain Category 2

Terrain Category 2.5

Terrain Category 3

All regions 1.07 1.00 0.94 0.88 0.83

NOTE: Terrain category multipliers for intermediate Terrain Categories (1.5 and 2.5) were found by interpolation.

TABLE A2

TOPOGRAPHIC MULTIPLIER (Mt)

Topographic class

Value of topographic multiplier (Mt) applied in calculation of the

N and C categories

Range of values calculated using AS/NZS 1170.2 that are included

in the class

SHIELDING MULTIPLIER (Ms)

Shielding class Shielding multiplier (Ms) Full shielding (FS) 0.85

Partial shielding (PS) 0.95 No shielding (NS) 1.00

A3.2 Terrain category

The definitions of terrain category in this Standard are consistent with those incorporated into AS/NZS 1170.2:2011 by its Amendment 2 (2012).

At serviceability and ultimate limit states wind speeds, the very strong winds tend to blow the top off short-wavelength waves and the water surface can be quite smooth. Closed waterbodies such as lakes, rivers and enclosed bays, therefore have minimal roughness and can be classed as Terrain Category 1 where they are more than 200 m but less than 10 km wide. However, larger water bodies such as open oceans and seas can have long wavelength waves which rise as they enter the shallower near-shore water. This gives these waterbodies a slightly rougher surface near the land and they can therefore be classified as Terrain Category 1.5 in their effect on one and two storey houses.

Terrain Category 1.5 specifically addresses the roughness of near shore open waterbodies such as seas and oceans adjoining housing land.

Where a water body is less than 200 m wide (i.e. the wind blows for less than 200 m across the top of the water in order to pass over the site under consideration) the wind does not have sufficient time over the water to increase its velocity enough for the terrain category to change. However, where the wind passes over the water body for more than 200 m, the time over smooth terrain is sufficient to increase the wind velocity to that of smooth terrain (i.e.

Terrain Category 1). Where the water body is large (i.e. the wind has been blowing over the water for more than 10 km), then wind has the chance to develop long wavelength waves that will shoal on reaching the shore irrespective of the wind. Hence:

(a) Water bodies less than 200 m wide in the direction that the wind is blowing to affect a site do not affect the terrain category.

(b) Water bodies greater than 200 m wide, but less than 10 km wide in the direction that the wind is blowing to affect a site are deemed to be Terrain Category 1.

(c) Only water bodies greater than 10 km wide in the direction that the wind is blowing to affect a site are deemed to be Terrain Category 1.5.

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Terrain Category 2.5 addresses acreage subdivisions where the house density is less than 10 per hectare. This level of roughness is also appropriate for some wooded agricultural land or farms with very high crops such as sugar cane.

Large trees offer some surface roughness. Even if they are denuded in very strong winds, the standing trees contribute to the surface roughness. This is a very different concept to shielding where a denuded tree is not able to offer protection to a nearby structure. The density of trees is important in assigning terrain categories. Where trees are large and robust (similar size to houses) then wooded areas with:

(i) Fewer than 2 large trees per hectare can be categorized as TC2.

(ii) Between 2 and 10 large trees per hectare can be categorized as TC2.5.

(iii) More than 10 large trees per hectare can be categorized as TC3.

In some cases, the 500 m radius circle may contain combinations of smooth features. For example, a small lake with diameter less than 200 m may be adjoined by a park also with width less than 200 m. However, the combine width of smooth features is greater than 200 m and the lake should be considered as part of the park, giving limiting terrain category for the building at the centre of the 500 m radius circle as Terrain Category 2.

Other combinations of smooth features may be less apparent. For example, a freeway reserve of width 150 m may be adjacent to a creek and reserve of width 100 m. Here the total width of smooth features is greater than 200 m, so must be considered as a region of Terrain Category 2.

Where the smooth features do not adjoin they do not have to be combined. For example, a freeway reserve of width 150 m and a creek reserve of width 100 m separated by two rows of houses can be treated as two separate smooth features, each with a width of less than 200 m. The two separated features do not affect the terrain category.

Appendix C has some illustrations of the application of terrain classification. It shows that within 500 meters of a change in terrain category, the lowest terrain category applies to all housing.

A3.3 Topographic class

The topographic class in AS 4055 is derived from the topographic multipliers used in AS/NZS 1170.2 as shown in Table A2.

A3.4 Shielding

In assessing shielding, permanent obstructions of the same size as the house designed with a frequency of more than 10 per hectare within 100 m of the site, can be considered as providing full shielding. This means that two full rows of housing are required on all sides to give full shielding. If only one full row of housing is available on one side, then the site is categorized as ‘partially shielded’. If there are no shielding obstructions on at least one side, then it is classified as ‘not shielded’.

In assessing shielding, a reasonable estimate should be made about infill development in the

Recent amendments of AS/NZS 1170.2 provide that where buildings are situated on steeply rising land, the roof of a building being designed will not be shielded by the roof of a similar-sized building lower on the slope. This Standard has simplified the AS/NZS 1170.2 provisions by relating the shielding to the topographic class. Higher topographic classes are associated with steeper slopes, for which full shielding is not appropriate. Hence, full shielding may only be used on slopes corresponding to Topographic Classes T0, T1, and T2. It is recognized that some partial shielding may be possible for slightly higher slopes, so partial shielding is appropriate for Topographic Classes T0, T1, T2, and T3. No shielding can be recognized where the slope is sufficient for T4 or T5.

A4 COMMENTARY ON PRESSURE COEFFICIENTS (SECTION 3)

The pressure coefficients given in Section 3 have been based on AS/NZS 1170.2. The following criteria were used:

(a) The house comprises basically rectangular bluff bodies within the geometric shape limits given in Clause 1.5.

(b) Roofs are of normal shape (for example, not arched).

(c) Net pressure coefficients comprise the addition of internal and external pressures on the building envelope. The combination factor (K_c in AS/NZS 1170.2) is included to take account of the fact that peak pressures occur on different surfaces at slightly different times.

(d) Pressures include the effects of dominant openings for Regions C and D only.

(e) In order to justify the use of lower internal pressures in Regions A and B, all elements of the cladding need to be designed to withstand the design winds.

(f) Pressures include the effects of local high-pressure zones on the leading edges of surfaces of the building envelope.

The pressure factors given for the 1200 mm zones near corners and near edges of roofs reflect a simplification of the AS/NZS 1170.2 factors for peak local pressures known to occur in these areas of buildings. Comparisons of pressure coefficients from the simplified local pressure model in this Standard and the more complex model in AS/NZS 1170.2 showed that the underestimations and overestimations were relatively small.

The local pressure model in this Standard recognizes that the high local pressure factor must act on around 25% of a structural unit in order to classify it as attracting higher pressures. Hence, windows with 25% or more width of a single pane within 1200 mm of the building edge are classified for pressures as SC (corner). A single pane will respond independently of the rest of the elements in the window. For doors, the single element is the opening leaf on a single door, one opening leaf on a double door. Hence, doors with 25% or more of the width of one opening leaf within 1200 mm of the building edge are classified as SC not G.

A5 COMMENTARY ON PRESSURES FOR DETERMINATION OF RACKING FORCES (SECTION 5)

A5.1 General, notation and assumptions A5.1.1 General

This Paragraph describes how the equivalent pressures tabulated in Section 5 for use with projected areas, for the calculation of racking loads to be resisted by bracing have been derived. The methods of determination of equivalent pressures for the calculation of racking forces in orthogonal directions for single or upper storey, for lower of two storeys and for subfloor level are given.

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A5.1.2 Notation

Notation symbols for Paragraph A5 are closer to the notation in AS/NZS 1170.2. This is so that its origin in that document can be followed to the source. The notation in Paragraph A5 is as follows:

b = plan dimension of building or part of building perpendicular to wind direction, in metres (see AS/NZS 1170.2)

C_pt,roof = combined pressure coefficient for the windward and leeward roof areas

C_pt,wall = combined pressure coefficient for the windward and leeward walls

d = plan dimension of building or part of building parallel to the wind direction, in metres (see AS/NZS 1170.2)

H_F = depth of upper floor, in metres

H_L = height, floor to ceiling for lower storey of two storeys, in metres H_u = height, floor to ceiling for single or upper storey, in metres h = height to eaves, in metres (see AS/NZS 1170.2)

K_a = area reduction factor K_c = pressure combination factor

L = length of building, in metres (see Figure A5.1)

q_u = free stream dynamic gust pressure, in kPa, for the ultimate limit state in

In document AS 4055-2012 Wind loads for housing.pdf (Page 27-69)