Timber Framing Code
SECTION 1. WALL AND ROOF FRAMING
Q1. Truss Span
The truss span should be 6-30m, and the distance between the trusses should be 0.75 to 1.25 m with 4m steel purlins.
The truss span should be calculated using a pitch = r/0.5 with r= 450mm
The following is a sketch for the truss span
Q2. Common Wall studs
The studs should have the following parameters.
Spacing 16*24 inches apart.
Q3. Bottom Plane Parameters
The bottom plans should be 47*64 inches
The slope (X in 12)
Q4. Lintel to Dining Room window assumed to be opening of 2110 mm.
Lintel length should be determined depending on the load uniformity distribution.
For window assumed to have an opening of 2110mm, the lintel length should be 215*100mm.
Q5. Jamb Studs
2*55 inches
Q6. Top Plate
12*15 inches
Q7. Order length for the Lintel to Dining Room Window
=(1250*4)=5000mm
Q8.
If the trussed roof is replaced with a traditionally constructed coupled roof, then;
The rafter span
Then the Rafter Span = should be 2*6 with a maximum live load of 20lbs/ft
The table below illustrates the maximum rafter span
Q9. The nominated timber size= 5000*650mm and the nominated overhang size should be= 50mm*45mm
Q10. The under purlin= With an assumption that it has a continuous span of 2.4m, then the underpurlin from the hySpan should be 100mm.
Q11. The collar tie on the other hand is to be calculated using the lengths of the building.
The collar tie is assumed to go round the building; (50mm*100mm)*4
The collar tie therefore should have a length of 2000mm
Q12. 2560mm
SECTION 2- BRACING
Q13. Calculate the height of the building
To calculate the height of the building, it is important to evaluate on the height of the top storey that is measured from the upper floor surface of the top floor to the ground. Additionally, the height of the building will be an exclusion of the roof top areas and any other top storey on the building. In order to calculate the height of the building will be;
Assuming that the height of the observer= 1.5m, the horizontal distance is 450m and the vertical angle is 22.50 , and the slope angle is 300 then the height of the building is H +h
From the details assigned on the table 9.6, then the height of the building can be accrued from the using the diagram below.
H= (d.tan 0) + (d. tan a)= d. (tan 0 +tan a)
Replacing the values on the above formula we obtain that the height of the building is
H= 4.5m (tan 22.5 + tan 30)
H= 4.46203m
Q14. Bracing Units
To evaluate on the bracing units i.e the direction of wind towards the elevation 3 and elevation 4, it is important to evaluate on classification of wind. From the wall systems table, the wind classification is assumed to be N2 33m/s . We then determine the pressure of the wind from both elevation 3 and 4. In this case, we require the roof pitch, the width of the building and the material of the walls and their nature as well.
The diagram below clearly indicates on how to evaluate on the bracing.
To determine the area of elevation for both winds, the complex elevations should be characterized by flat walls and a sloping roof.
Wind Direction 3
The area of the roof is 5.4m2
(7.2 *1.5*0.5)
The area of the wall is 8.64m2
(7.2 *1.2) =8.64m2
Therefore the total area of the wind for elevation 3 is (5.4 +8.64)= 14.04m2
Wind Direction 4
The area of the roof is 24.3m2 (16.2*1.5)
The area of the wall is 19.44m2 (16.2*1.2)
The total bracing for the wind direction for elevation 4 is (24.3 +19.44) =43.74m2
Q.15 Combination of the bracing Units
Drawing a reference from the bracing units in Q14 above, it is necessary to evaluate on the combinations of the bracing units for wind direction for elevation 3 and elevation 4.
To evaluate on the combinations of the bracing units it is necessary to calculate the racking force for both directions of wind. In this case, we evaluate the racking force (Kn)= wind pressure (kPa) * the area of elevation.
In this case therefore, the total combination racking force for wind direction in elevation 3 is (14.04m2 *0.92) =12.9Kn
The total combination racking force for wind direction in elevation 4 is
43.74m2 * 0.6 = 26.2Kn
Additionally, it is also vital to calculate the racking force in reference to the diagonal bracing of the building. Drawing from table 9.6
The racking force for diagonal bracing is given in Kn/m= Length of the wall * the bracing capacity. The braces are set to be kept in opposing pairs in order not to allow the individual braces exceeding the 4.46 wall height. For this building, the combination of the bracing units for direction of wind in elevation 3 and elevation 4 should be the maximum length of the wall then braced by an individual brace which turns out to be 2.4m.
SECTION 3- SPECIFIC FIXINGS (TIE-DOWNS)
Q16 Bottom plate to slab with spacing of 1800mm
The requirements for the specific fixings of a bottom plate to slab include the anchors that are used fro fixing the bottom plates on to the concrete slab on the ground floors for a timber frame construction. The anchors should be able to deal with the force from all the three directions. Including the force that comes from across the wall (out-of plane shear), the force along the wall (in-plane shear) and the uplift force also referred to as the tension. For a bottom plate to slab with a spacing of 1800mm, then the fixing the bottom plates to the slab should have the following requirements.
- There should be tested branded anchors that should be specifically inserted into the concrete once it has cured sufficiently.
- There should exist cast in anchors that consist of M12 bolts that are specifically casted into the concrete with a combination of either 55*3 mm round washers and 3*50*50mm square washers. Additionally, there should be an availability of wide range of exclusive anchors into the predrilled holes, and anchors that are chemically grouted into the drilled holes and making expansions on the wedge anchors.
Q17. Studs to top and bottom plates
In regard to the studs screwed on the top and the bottom plates, the studs should be designed in a manner that they should be removable fixings for the top and the bottom plates. The studs should have the following characteristics; they should be easy and quick to install. In this case, drill a hole on the correct location on the slab floor. The timber should be aligned, framed and installed on the screw stud with the help of either a wrench, manual socket or a power driver. The stud should be removed easily. Finally, the studs should have the minimal capability to cause any damage on the top and the bottom plates as they do not have an expanding sleeve or wedge that is used in sustaining the expansion force. In this case, the studs should have the following features depending on where they are placed.
Additionally, the screw type of stud should be ensured that they can fit into meeting the uplift capacity of the top and the bottom plates depending on the bracing units. Additionally, the studs should have the test results in order to demonstrate that they meet the NZS 3604 requirements for their intended purposes. In conclusion, the studs should have an adequate cover over the bottom and the top plates.
Q18. Rafter Spacing of 600mm
The rafter spacing of 600mm requirements should be specifically categorized on the spacing and the edges. The rafter spacing should not give edge distance dimensions for the proprietary anchors as the dimensions depend entirely on the slab edges and the products as well. The rafter spacing should have the following characteristics;
They should have a maximum of 600mm centers for the in-situ slab floors. Additionally, they should be featured by 600mm centers maximum where by the slab edges should be formed using the masonry header blocks. Finally, there should be no more than 150mm space from every end of every plate.
