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 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) (b) (c) (d) Determine the wind classification = N 3 Determine the wind pressure Determine area of elevation Calculate racking force
Refer to page 112 – Section 8 – AS 1684. 2 8. 3. 2 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 Area 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.
Permanent Wind Bracing Length of Building 14. 640 Width of Building Roof Pitch 7. 570 300 Rise of Roof Floor to ceiling height 2. 700 m Wind Classification 2. 100 m N 3 Using the Plan & previous information from Roof and Wall framing Calculations fill in the above information (7. 570 ÷ 2) – 0. 150 = 3. 635 × tan 30 = 2. 098 Rise = 2. 100 m
Wind Direction 2 Wind Direction 1
Calculate the area of elevation for Wind Direction 1 7 070 3 785 1 350 2 100 3 785 14 640 x 1 350 = 19. 764 m 2 7 070 x 2 100 = 14. 847 m 2 3 785 x 2 100 = 7. 949 m 2 Total Area 42. 56 m 2
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 90 O to a ridge and for wind speeds N 1, N 2, N 3 & N 4.
8. 3. 4 Racking force The total racking force, in k. N, shall be calculated as follows: Projected area of elevation (m 2) X Lateral wind pressure (k. Pa) = Total racking force
Wind Direction 1 Wind Speed / N 3 Roof Pitch 300 Building Width Pressure / k. Pa = 1. 1
8. 3. 4 Racking force The total racking force, in k. N, shall be calculated as follows: Projected area of elevation (42. 6 m 2) X Lateral wind pressure (1. 1 k. Pa) = Total racking force (46. 9 k. N) – Wind Direction 1
Side elevation (Wind direction 1) Area 42. 6 m 2 Wind Pressure 1. 1 k. Pa (table 8. 2 p 118) Total Racking Force 46. 9 KN Nominal Bracing KN Bracing Required KN Fill in known information (Area, Pressure, Raking Force) Calculate Nominal Bracing
Refer to page 140 – Section 8 – AS 1684. 2 8. 3. 6. 2 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.
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. 380 m 16. 380 x 0. 45 k. N/m = 7. 4 k. N 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. 900 m 16. 900 x 0. 75 k. N/m = 12. 7 k. N
Side elevation (Wind direction 1) Area 42. 6 m 2 Wind Pressure 1. 1 k. Pa (table 8. 2 p 118) Total Raking Force 46. 9 KN Nominal Bracing KN 20 Bracing Required 26. 9 KN Fill in Nominal Bracing total of Single & Two Sided walls 7. 371 + 12. 675 = 20. 046 k. N Check that nominal bracing is 50% or less than total racking force Bracing required = Total Racking Force – Nominal Bracing. 46. 9 – 20 = 26. 9 k. N of Bracing Required.
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. Figure 8. 5 Location of Bracing
Select Bracing Type ‘G’ Method B (p 144) Method B = 6. 0 KN/m x 1. 2 m (sheet width) 1 Sheet = 7. 2 KN 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. 9 k. N Required & 28. 8 k. N given in type ‘G’. 4 Type ‘G’ sheets will meet the requirements.
(G) Bracing Type ‘G’ – Table 8. 18 page 144 AS 1684. 2 - 2006
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. Figure 8. 5 Location of Bracing
Refer page 150 of 1684. 2 (2006) Wind Speed Ceiling Width Roof Pitch Spacing of Bracing Calculate spacing of Bracing for Wind Direction 2
Wind Direction 1 Braces are too far apart. We must place intermediate braces < 6. 1 m apart
Wind Direction 1 Braces are too far apart. We must place intermediate braces < 6. 1 m apart
Wind Direction 2 Repeat for Wind Direction 2
Calculate the area of elevation for Wind Direction 2 3 785 1 350 2 100 3 785 7 570 x 1 350 = 10 220 m 2 3 785 x 2 100 = 7 949 m 2 Total Area 18. 1 m 2
Refer page 122 of 1684. 2 (2006) Wind Direction 2 Wind Speed Roof Pitch Building Width Pressure / k. Pa 1. 2 k. Pa
8. 3. 4 Racking force The total racking force, in k. N, shall be calculated as follows: Projected area of elevation (18. 1 m 2) X Lateral wind pressure (1. 2 k. Pa) = Total racking force (21. 7 k. N) – Wind Direction 2
End elevation (Wind direction 2) Area 18. 1 Wind Pressure 1. 2 Total Racking Force 21. 7 m 2 k. Pa (table 8. 4 p 122) KN Nominal Bracing KN Bracing Required KN Fill in known information (Area, Pressure, Raking Force) Calculate Nominal Bracing
Wind Direction 2 Calculate all single sided (Gyprock lined) walls for Nominal Bracing 2 x (14. 640 – 0. 480) = 28. 320 m 28. 320 – openings = nominal S/S length Refer to window schedule for window sizes
Window Schedule: Window W x H W 9 Bedroom 1 1. 800 1. 550 W 1 Bedroom 2 1. 200 1. 550 W 8 Bedroom 3 1. 200 1. 550 W 2 Bath & WC 1. 800 0. 900 W 3 Laundry 1. 350 0. 900 W 4 Kitchen 1. 650 0. 900 W 5 Dining 1. 200 1. 550 W 6 Living 1. 850 1. 650 W 7 Family 1. 850 1. 650 D 2 Entry 1. 350 2. 060 D 1 Kitchen 0. 900 2. 060 Total length of opening widths = 16. 150
Wind Direction 2 28. 320 – openings = nominal S/S length 28. 320 – 16. 150 = 12. 170 m 12. 170 x 0. 45 k. N/m = 5. 477 k. N Now Calculate double or Two Sided (Gyprock Lined) Walls
Wind Direction 2 Two Sided walls for Nominal Bracing (11. 510 + 4. 300) – 5 doors @ 0. 900 = 15. 810 – 4. 500 = 11. 310 m 11. 310 x 0. 75 k. N/m = 8. 483 k. N
End elevation (Wind direction 2) Area 18. 1 m 2 Wind Pressure 1. 2 k. Pa (table 8. 4 p 122) Total Racking Force 21. 7 KN Nominal Bracing 10. 85 KN Bracing Required 10. 85 KN Fill in Nominal Bracing total of Single & Two Sided walls 5. 477 + 8. 483 = 13. 960 k. N Check that nominal bracing is 50% or less than total raking force Nominal Bracing is over 50% - Therefore Total raking force is to be halved 21. 7 ÷ 2 = 10. 85 k. N
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. Figure 8. 5 Location of Bracing
Refer page 150 of 1684. 2 (2006) Wind Speed Ceiling Width Roof Pitch Spacing of Bracing Calculate spacing of Bracing for Wind Direction 2
Select Bracing Type ‘G’ Method B (p 144) Method B = 6. 0 KN/m x 1. 2 m (sheet width) 1 Sheet = 7. 2 KN - Therefore 2 x 7. 2 = 14. 4 k. N Meets the racking force requirement, but does not meet the requirements of clauses 8. 3. 6. 6 & 8. 3. 6. 7, Therefore those requirements need to be met. Braces need to start at the corners and no further apart than 6. 700 m maximum Spacings to Wind Direction 2 Mark braces on floor plan.
Wind Direction 2 Bracing for Wind Direction 2 complete.
Select Bracing Type ‘G’ Method B (p 144) Method B = 6. 0 KN/m x 1. 2 m (sheet width) 1 Sheet = 7. 2 KN - Therefore 2 x 7. 2 = 14. 4 k. N Refer to 8. 3. 6. 5 pg 148: panel length 600 equals strength of 900 Divided by two. i. e. . 9 x 6 Kn/m= 5. 4 / 2=2. 7 (3 x 2. 7) + (. 9 x 6 k. N) + 7. 2 = 20. 7 Braces need to start at the corners and no further apart than 6. 700 m maximum Spacings to Wind Direction 2 Mark braces on floor plan.
Wind Direction 2 Bracing for Wind Direction 2 complete.
Exercise 1 Completed
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