2182 D - Timber Framing Code

Wall Bracing

Class Exercise 1

Reference Material

• Class Exercise 1 Roofing & Wall Framing notes.

• Floor Plan from Exercise 1.

• AS 1684 .2 (2006) Non Cyclonic Code.

Refer to page 112 – Section 8 – AS 1684.2

8.3.1 General8.3.1 General Bracing shall be designed and provided for each storey of the house and for the subfloor, where required, in accordance with the following procedure:

(a) Determine the wind classification

(b) Determine the wind pressure

(c) Determine area of elevation

(d) Calculate racking force

= N3

Refer to page 112 – Section 8 – AS 1684.2

8.3.2 8.3.2 Wind pressure on the building Wind pressure on the building

Wind pressures on the surfaces of the building depend on the wind classification, width of building and roof pitch. Tables 8.1 to 8.5 give pressures depending on these variables.(AS 1684.2, pages 116 – 124)

Pressures are given for single storey and upper storey of two storeys for both long and short sides of the building, and lower storey of two storeys or subfloor for both long and short sides of the building.

Refer to page 112 – Section 8 – AS 1684.2

8.3.3 8.3.3 Area of elevationArea of elevation 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.

Length of Building

Width of Building

Roof Pitch Rise of Roof

Floor to ceiling height

Wind Classification

Permanent Wind Bracing

Using the Plan & previous information from Roof and Wall framingCalculations fill in the above information

14.640

7.570

300

2.700m

N3

2.100m

(7.570 ÷ 2) – 0.150 = 3.635

3.635 × tan 30 = 2.098

Rise = 2.100m

Wind Direction 1

Win

d D

irec

tio

n 2

Calculate the area of elevation for Wind Direction 1

3 7857 0703 785

14 640

2 1

00

1 3

50

14 640 x 1 350 = 19.764 m2

7 070 x 2 100 = 14.847m2

3 785 x 2 100 = 7.949 m2

Total Area 42.56 m2

Refer to page 116 – Section 8 – AS 1684.2

8.3.4 Racking force

The total racking force for each storey or level of the building shall be the product of the projected area of elevation of the building multiplied by the lateral wind pressure determined from Tables 8.1 to 8.5. The racking force shall be calculated for both directions (long and short sides) of the building.

Table 8.2 is used for determining the pressure on single or upper storey elevations where the wind direction is at 90O to a ridge and for wind speeds N1, N2, N3 & N4.

8.3.4 Racking force

The total racking force, in kN, shall be calculated as follows:

Projected area of elevation (m2)

X

Lateral wind pressure (kPa)

=

Total racking force

TABLE 8.2

PRESSURE (kPa) ON PROJECTED AREA—SINGLE STOREY OR UPPER OF TWO STOREY—LONG LENGTH OF BUILDING—HIP OR GABLE ENDS

W

WW ind d ire c t ion

W ind d ire c t ion

W (m) Roof pitch (degrees)

N3

0 5 10 15 20 25 30 35

4.0 1.3 1.2 1.0 0.95 0.96 1.1 1.2 1.2

5.0 1.3 1.1 1.00 0.89 0.91 1.1 1.2 1.2

6.0 1.3 1.1 0.95 0.85 0.91 1.1 1.2 1.2

7.0 1.3 1.1 0.91 0.82 0.93 1.1 1.1 1.2

8.0 1.3 1.0 0.88 0.79 0.94 1.1 1.1 1.2

9.0 1.3 0.99 0.84 0.77 0.95 1.1 1.1 1.2

10.0 1.3 0.97 0.81 0.75 0.95 1.1 1.1 1.2

11.0 1.3 0.94 0.78 0.75 0.97 1.1 1.1 1.2

12.0 1.3 0.92 0.74 0.76 0.98 1.1 1.1 1.2

13.0 1.3 0.90 0.71 0.77 0.99 1.1 1.1 1.2

14.0 1.3 0.87 0.68 0.78 1.0 1.1 1.1 1.2

15.0 1.3 0.85 0.65 0.79 1.0 1.1 1.1 1.2

16.0 1.3 0.83 0.62 0.79 1.0 1.1 1.1 1.2

Wind Direction 1

Wind Speed / N3

Roof Pitch 300

Building Width

Pressure / kPa = 1.1

8.3.4 Racking force

The total racking force, in kN, shall be calculated as follows:

Projected area of elevation

(42.6m2)

X

Lateral wind pressure

(1.1kPa)

= Total racking force

(46.9kN) – Wind Direction 1

Side elevation (Wind direction 1)

Area m2

Wind Pressure kPa (table 8.2 p 118)

Total Racking Force KN

Nominal Bracing KN

Bracing Required KN

Fill in known information (Area, Pressure, Raking Force)

42.6

1.1

46.9

Calculate Nominal Bracing

8.3.6.2  Nominal wall bracing Nominal wall bracing is wall framing lined with sheet materials such as plywood, plasterboard, fibre cement or hardboard, or the like, with the wall frames nominally fixed to the floor and the roof or ceiling frame.

The maximum amount that can be resisted by nominal wall bracing is 50% of the total racking forces determined from Clause 8.3.4 . Nominal wall bracing shall be evenly distributed throughout the building. If this is not the case, the contribution of nominal bracing shall be ignored.

The minimum length of nominal bracing walls shall be 450 mm.

Refer to page 140 – Section 8 – AS 1684.2

TABLE 8.17

NOMINAL SHEET BRACING WALLS

Method Bracing capacity (kN/m)

Sheeted one side only 0.45 kN/m

Sheeted two sides 0.75 kN/m

8.3.6.2  Nominal wall bracing (Cont.)

The bracing capacity of nominal bracing is scheduled in Table 8.17.

Wind Direction 1

Calculate all single sided (Gyprock lined) walls for Nominal Bracing

2 x (7.570 – 0.480) + (2 x 1.100) = 16.380m 16.380 x 0.45kN/m = 7.4kN

Now Calculate double or Two Sided (Gyprock Lined) Walls

Wind Direction 1

Two Sided walls for Nominal Bracing

(4 x 2.500) + (1 x 2.400) + (1 x 3.500) + (2 x 0.500) = 16.900m

16.900 x 0.75kN/m = 12.7kN

Side elevation (Wind direction 1)

Area m2

Wind Pressure kPa (table 8.2 p 118)

Total Raking Force KN

Nominal Bracing KN

Bracing Required KN

42.6

1.1

46.9

Fill in Nominal Bracing total of Single & Two Sided walls

7.371 + 12.675 = 20.046 kN

20

Bracing required = Total Racking Force – Nominal Bracing.

Check that nominal bracing is 50% or less than total racking force

46.9 – 20 = 26.9kN of Bracing Required.

26.9

Refer to page 148 – Section 8 – AS 1684.2

8.3.6.6 Location and distribution of bracing

Bracing shall be approximately evenly distributed and shall be provided in both directions (see Figure 8.5).

Bracing shall initially be placed in external walls and where possible at the corners of the building.

W in dd ire c t io n W in d

d ire c t io n

AA

B

B

C

C

D

D

E

T o t a l b r a c i n g s t r e n g t h = A + B + C + D , e t c .

N O T E : A , B , C a n d D a r e t h e d e s i g n s t r e n g t h s o f i n d i v i d u a l b r a c i n g w a l l s .

( a ) R i g h t a n g l e s t o l o n g s i d e ( b ) R i g h t a n g l e s t o s h o r t s i d e

Figure 8.5 Location of Bracing

Select Bracing

Bracing Type ‘G’ Method B (p 144)

Method B = 6.0 KN/m x 1.2m (sheet width) 1 Sheet = 7.2KN Therefore 4 x 7.2 = 28.8 KN

Reference, 8.3.6.6 Location and distribution of bracing

Check bracing required to amount of ‘G’ type bracing.

26.9kN Required & 28.8kN given in type ‘G’.

4 Type ‘G’ sheets will meet the requirements.

(h) Plywood P lywood shall be nailed to frame using 302.8 flathead nailsor equivalent.

For M ethod A, M 12 rods shall be used at each end of sheathed section topplate to bottom plate/floor frame. M ethod B has no rods but sheathing shallbe nailed to top and bottom plates and any horizontal joints at 50 mmcentres.

NOTE: For plywood fixed to both sides of the wall, see Clause 8.3 .6.5.

M inimum plywoodthickness (mm)

Bracing Type ‘G’ – Table 8.18 page 144 AS 1684.2 - 2006

(G)

Wind Direction 1

Mark Plan with Bracing Sheets to support Wind Direction 1

Refer to page 148 – Section 8 – AS 1684.2

8.3.6.6 Location and distribution of bracing

Bracing shall be approximately evenly distributed and shall be provided in both directions (see Figure 8.5).

Bracing shall initially be placed in external walls and where possible at the corners of the building.

W in dd ire c t io n W in d

d ire c t io n

AA

B

B

C

C

D

D

E

T o t a l b r a c i n g s t r e n g t h = A + B + C + D , e t c .

N O T E : A , B , C a n d D a r e t h e d e s i g n s t r e n g t h s o f i n d i v i d u a l b r a c i n g w a l l s .

( a ) R i g h t a n g l e s t o l o n g s i d e ( b ) R i g h t a n g l e s t o s h o r t s i d e

Figure 8.5 Location of Bracing

TABLE 8.20

MAXIMUM SPACING OF BRACING WALLS — N3 WIND CLASSIFICATION

Maximum bracing wall spacing (m)

Roof pitch (degrees)Ceiling

depth (m)0 5 10 15 17.5 20 25 30 35

4 5.9 6.6 7.4 7.5 7 6.4 5.1 4.4 4.2

5 7.4 8.3 9 9 8.6 7.9 6 5 4.7

6 8.9 9 9 9 9 8.8 6.7 5.6 5.1

7 9 9 9 9 9 9 7.1 6.1 5.5

8 9 9 9 9 9 9 7.6 6.7 5.7

9 9 9 9 9 9 9 7.9 7.2 5.9

10 9 9 9 9 9 9 8.4 7.9 6.2

11 9 9 9 9 9 9 8.7 7.9 6.4

12 9 9 9 9 9 9 9 7.9 6.6

13 9 9 9 9 9 9 9 8.1 6.6

14 9 9 9 9 9 9 9 8.3 6.7

15 9 9 9 9 9 9 9 8.4 6.8

16 9 9 9 9 9 9 9 8.6 6.9

Refer page 150 of 1684.2 (2006)

Calculate spacing of Bracing for Wind Direction 2

Wind Speed

Ceiling Width

Roof Pitch

Spacing of Bracing

Wind Direction 1

Braces are too far apart. We must place intermediate braces < 6.1m apart

Wind Direction 1

Braces are too far apart. We must place intermediate braces < 6.1m apart

Win

d D

irec

tio

n 2

Repeat for Wind Direction 2

Calculate the area of elevation for Wind Direction 2

3 7853 785

7 570

2 1

00

1 3

50

7 570 x 1 350 = 10 220 m2

3 785 x 2 100 = 7 949 m2

Total Area 18.1m2

T A B L E 8 . 4

P R E S S U R E ( k P a ) O N P R O J E C T E D A R E A — S I N G L E S T O R E Y O R U P P E R O FT W O - S T O R E Y — S H O R T E N D O F B U I L D I N G — H I P E N D S

W in d d ire c t io n

W in d d ire c t io n

W ( m ) R o o f p i t c h ( d e g r e e s )

N3

0 5 10 15 20 25 30 35

4.0 1.4 1.3 1.3 1.2 1.2 1.2 1.3 1.3

5.0 1.4 1.3 1.2 1.2 1.1 1.2 1.3 1.2

6.0 1.4 1.3 1.2 1.1 1.1 1.2 1.2 1.2

7.0 1.4 1.3 1.2 1.1 1.1 1.2 1.2 1.2

8.0 1.4 1.3 1.1 1.1 1.1 1.2 1.2 1.2

9.0 1.4 1.2 1.1 1.0 1.1 1.2 1.2 1.2

10.0 1.4 1.2 1.1 1.0 1.1 1.2 1.2 1.2

11.0 1.4 1.2 1.1 1.0 1.1 1.2 1.2 1.2

12.0 1.4 1.2 1.0 1.0 1.1 1.2 1.2 1.2

13.0 1.4 1.2 1.00 1.0 1.1 1.2 1.2 1.2

14.0 1.4 1.1 0.97 1.00 1.1 1.2 1.2 1.2

15.0 1.4 1.1 0.94 1.00 1.1 1.2 1.2 1.2

16.0 1.4 1.1 0.92 1.00 1.1 1.2 1.2 1.2

Wind Direction 2

Wind Speed

Roof Pitch

Building Width

Pressure / kPa1.2kPa

Refer page 122 of 1684.2 (2006)

8.3.4 Racking force

The total racking force, in kN, shall be calculated as follows:

Projected area of elevation

(18.1m2)

X

Lateral wind pressure

(1.2kPa)

= Total racking force

(21.7kN) – Wind Direction 2

End elevation (Wind direction 2)

Area m2

Wind Pressure kPa (table 8.4 p 122)

Total Racking Force KN

Nominal Bracing KN

Bracing Required KN

Fill in known information (Area, Pressure, Raking Force)

18.1

1.2

21.7

Calculate Nominal Bracing

Win

d D

irec

tio

n 2

Calculate all single sided (Gyprock lined) walls for Nominal Bracing

2 x (14.640 – 0.480) = 28.320m 28.320 – openings = nominal S/S length

Refer to window schedule for window sizes

Window Schedule:

Window W x H

W9 Bedroom 1 1.800 1.550

W1 Bedroom 2 1.200 1.550

W8 Bedroom 3 1.200 1.550

W2 Bath & WC 1.800 0.900

W3 Laundry 1.350 0.900

W4 Kitchen 1.650 0.900

W5 Dining 1.200 1.550

W6 Living 1.850 1.650

W7 Family 1.850 1.650

D2 Entry 1.350 2.060

D1 Kitchen 0.900 2.060

Total length of opening widths = 16.150

Win

d D

irec

tio

n 2

28.320 – openings = nominal S/S length

28.320 – 16.150 = 12.170m 12.170 x 0.45kN/m = 5.477kN

Now Calculate double or Two Sided (Gyprock Lined) Walls

Win

d D

irec

tio

n 2

Two Sided walls for Nominal Bracing

(11.510 + 4.300) – 5 doors @ 0.900 = 15.810 – 4.500 = 11.310m

11.310 x 0.75kN/m = 8.483kN

End elevation (Wind direction 2)

Area m2

Wind Pressure kPa (table 8.4 p 122)

Total Racking Force KN

Nominal Bracing KN

Bracing Required KN

18.1

1.2

21.7

Fill in Nominal Bracing total of Single & Two Sided walls

5.477 + 8.483 = 13.960 kN

Check that nominal bracing is 50% or less than total raking force

Nominal Bracing is over 50% - Therefore Total raking force is to be halved21.7 ÷ 2 = 10.85 kN

10.85

10.85

Refer to page 148 – Section 8 – AS 1684.2

8.3.6.6 Location and distribution of bracing

Bracing shall be approximately evenly distributed and shall be provided in both directions (see Figure 8.5).

Bracing shall initially be placed in external walls and where possible at the corners of the building.

W in dd ire c t io n W in d

d ire c t io n

AA

B

B

C

C

D

D

E

T o t a l b r a c i n g s t r e n g t h = A + B + C + D , e t c .

N O T E : A , B , C a n d D a r e t h e d e s i g n s t r e n g t h s o f i n d i v i d u a l b r a c i n g w a l l s .

( a ) R i g h t a n g l e s t o l o n g s i d e ( b ) R i g h t a n g l e s t o s h o r t s i d e

Figure 8.5 Location of Bracing

TABLE 8.20

MAXIMUM SPACING OF BRACING WALLS — N3 WIND CLASSIFICATION

Maximum bracing wall spacing (m)

Roof pitch (degrees)Ceiling

depth (m)0 5 10 15 17.5 20 25 30 35

4 5.9 6.6 7.4 7.5 7 6.4 5.1 4.4 4.2

5 7.4 8.3 9 9 8.6 7.9 6 5 4.7

6 8.9 9 9 9 9 8.8 6.7 5.6 5.1

7 9 9 9 9 9 9 7.1 6.1 5.5

8 9 9 9 9 9 9 7.6 6.7 5.7

9 9 9 9 9 9 9 7.9 7.2 5.9

10 9 9 9 9 9 9 8.4 7.9 6.2

11 9 9 9 9 9 9 8.7 7.9 6.4

12 9 9 9 9 9 9 9 7.9 6.6

13 9 9 9 9 9 9 9 8.1 6.6

14 9 9 9 9 9 9 9 8.3 6.7

15 9 9 9 9 9 9 9 8.4 6.8

16 9 9 9 9 9 9 9 8.6 6.9

Refer page 150 of 1684.2 (2006)

Calculate spacing of Bracing for Wind Direction 2

Wind Speed

Ceiling Width

Roof Pitch

Spacing of Bracing

Select Bracing

Bracing Type ‘G’ Method B (p 144)

Method B = 6.0 KN/m x 1.2m (sheet width) 1 Sheet = 7.2KN - Therefore 2 x 7.2 = 14.4 kN

14.4 kN Meets the racking force requirement, but does not meet therequirements of clauses 8.3.6.6 & 8.3.6.7, Therefore those requirementsneed to be met.

Braces need to start at the corners and no further apart than 6.700m maximum Spacings to Wind Direction 2

Mark braces on floor plan.

Bracing for Wind Direction 2 complete.

Select Bracing

Bracing Type ‘G’ Method B (p 144)

Method B = 6.0 KN/m x 1.2m (sheet width) 1 Sheet = 7.2KN - Therefore 2 x 7.2 = 14.4 kN

Refer to8.3.6.5 pg 148: panel length 600 equals strength of 900Divided by two. i.e. .9 x 6Kn/m= 5.4 / 2=2.7

Braces need to start at the corners and no further apart than 6.700m maximum Spacings to Wind Direction 2

Mark braces on floor plan.

(3 x 2.7) + (.9 x 6kN) + 7.2 = 20.7

Bracing for Wind Direction 2 complete.

Exercise 1 Completed