2.0 Roof and Wall Sheeting
Selection of the metal sheeting for the roof and walls was obtained from the website www.bhpsteel.com.au. The wall sheeting must only resist wind loads, but the roof sheeting must resist wind loads and the weight of a person standing on the roof plus loads arising out of the stacking of materials. For the roof, the selected sheeting was Lysaght Klip-Lok 406 of 0.48 mm thickness and self weight of 5.71 kg/m2. For the walls, the selected sheeting was Lysaght Klip-Lok 406 of 0.42 mm thickness and self weight of 5.03 kg/m2. The manufacturer provided information regarding the maximum permissible end and internal spans and overhangs of the sheeting, this being taken into consideration when choosing sheeting rail spacing
2.1 Frame Spacing
The warehouse is 48 metres long and experiences shows that frame spacings in the range 6-8 metres are appropriate. 7 frames @ 8 metre centres or 9 frames @ 6 metre centres were two possible arrangements. After quite some discussion we opted for the 7 frames @ 8 metre centres.
Dimensions: Wall 7 frames @ 8m Spacing from top 0.95m, 1.8m, 1.8m & 0.95m Roof 7 frames @ 8m Spacing from top 1.75m, 2.2m, 2.2m, 1.75m, 1.8m & 0.2m
3.0 Loads
Industrial buildings are typically subjected to live, dead and wind loads. Loads such as snow and earthquake can be ignored as the building is located in surburban Melbourne. Dead, live and wind loads are calculated according to the provisions of AS1170.1
Dead Loads: They include the self weight of the roofing. Ceiling lining, ceiling joists and Insulation
Live Load: Pitched roof portal frames have non-trafficable roofs for which, according to AS1170.1, is 0.25kPa.
Wind Load: To design against wind, Australian Standard AS 1170.2 needs to be used. The first step is to determine what terrain category the structure it is situated within. Our structure is located in suburban Melbourne (region A) and according to the standards, it is in wind category 2 1/2.
The site wind speed was calculated with the aid of the following formula.
V sit,β= VR Md M (Z, CAT) Ms Mt
M (Z, CAT) = Terrain/height Multiplier at height Z
Ms = Shielding multiplier
Mt = Topographic Multiplier
VR = Regional Wind Speed
We obtained a value of 34.35 m/s (see Appendix for calculations)
We took the average height to determine the wind speed, which in this case was h = 6.203m.
The design of wind pressures and distributed forces was then obtained by the use of the following formula
P = (0.5 ρair )[Vdes,Ө]2 Cfig Cdyn
P= Design wind pressure acting normal to a surface
ρair = density of air (1.2 kg/m3)
Vdes,Ө = Building orthogonal design wind speed
Cfig = Aerodynamic shape factor
Cdyn = Dynamic response factor
The external wind pressure is the effect of the wind on the external surfaces of the building, and does change depending on its location, that is, if the wall is windward, leeward or side wall and for the roof, it depends on the distance from the windward edge
Longitudinal Wind
Windward wall: -0.399 kPa
Leeward Wall: -0.399 kPa
Roof: -0.510 kPa
Cross Wind:
Windward Wall: 0.496 kPa
Leeward Wall: -0.354 kPa
Side Wall: -0.368,-0.283, -0.170, -0.113 kPa in region 1, 2, 3 & 4 respectively
Roof: 1st Region: -0.510 kPa , 2nd Region: -0.283 kPa, 3rd Region: -0.170 kPa 4th Region: -0.113 kPa
The internal wind pressure is the effect of the wind upon the internal surfaces of the buildings. As before the internal pressure coefficient depended on the direction of the wind, and furthermore, wether the main door was open or not. The values used in each case involved the door being open as this produced the biggest loading.
Longitudinal Wind (Door Open): -0.818 kPa
Cross Wind (Door Open): -0.63 kPa
For calculations and relative diagrams refer to Appendix 2.
4.0 Purlins
The timber roof purlins are the roof sheeting rails. They must support the dead load (roof sheeting), live load, and wind load. The loads were calculated in accordance with AS 1170, and were spaced at a maximum of 2.2m (span of the purlins is 8m).
All purlins were designed to have the same dimensions and properties, as it simplifies the design and construction process. The type of timber chosen was GL17 Glulam. The member chosen for the purlins was designed to be structurally adequate under the most severe load cases. The three load cases considered for bending strength were:
• 1.35G (permanent load)
• 1.25G + 1.5Q (medium term)
• 0.9G + WU (permanent and wind load reversal)
Loads were changed from pressures into UDL’s along the purlin, taking the greatest loading into account. This was found to be the longitudinal wind with the door open.
WG = 0.383 KN/m
WQ = 0.55 KN/m
WU,E = 2.18 KN/m
WU,I = 1.8 KN/m
Design bending moments then needed to be calculated and was done by the following formula:
M*= WL2 /8
1.35G = 3.83 KNm
1.2G +1.5Q= 10.28 KNm
0.9G + WU = 24.4 KNm
Full calculations for the above load cases can be viewed in Appendix 3.
Trial cross sections for the purlins were needed in order to satisfy these bending moments and also for deflection.
The following equation found the deflections for each load case.
δ = 5WL4 / (384EIx)
Dead Load: 16.04mm < 20mm
Live Load: 10.85mm < 20mm
Wind Load: 39.18mm < 50mm
Design bending capacities had to be satisfied by the purlins also. The following formula was used to find the design bending capacity:
ΦM = ΦK1 K4 K6 K9 K11 K12 Fb’Z
Φ = Capacity Factor
K1 = Duration of load factor
K4 = Seasoning factor
K6 = Temperature factor
K9 = Strength sharing factor
K11 = Size factor
K12 = Stability Factor
Fb’= Strength in bending
Z= Section Modulus
Full calculations can be found in Appendix 3, where it shows values of K1 , Critical bending moment, slenderness coefficient (S1), etc.
Once all the coefficients were found, the design bending capacity was obtained for all three cases. They are shown below
1.35G………………………….ΦM 26.45 KNm > M* 3.83 KNm
1.2G + 1.5Q…………………...ΦM 43.6 KNm > M* 10.28 KNm
0.9G + WU …………………….ΦM 53.4 KNm > M* 29.4 KNm
5. Girts
The timber girts are the wall sheeting rails. They do not carry dead or live loads, only wind loads. The effect of the wind on the structure is outline in the wind calculations. The most severe case of combined internal and external pressures was used to design the girts. The maximum spacing for the wall girts is 1.8m and as before a span of 8m
Shown below are the load cases which we considered:
WU,E = 0.66 KN/m
WU,I = 1.47 KN/m
Design bending moment using the same formula as for the purlins, came out to be, M* = 17.04 KNm.
Again, a trial cross section (233 x 110) was needed which needed to satisfy bending and deflection
Wind Load: 39.18mm < 50mm
ΦM 40.86 KNm > M* 17.04 KNm
As for the end walls,the same girts will be used. The maximum spacing is also 1.8m and once again only wind loading will be taken into account. It is safe to assume that the same size timber would be satisfactory as the maximum load is no greater than the longitudinal wall.
Design computations for the girts are found in Appendix 4.
6. Portal Frame
A program called SPACEGASS was used to analyse the portal frame. It involves inputting the extreme design calculations to simulate the behaviour of the portal frame and then obtaining the bending moments and shear forces under these calculated loads. With the equation (ΦM = ΦK1 K4 K6 K9 K11 K12 Fb’Z) we were able to solve for Z, hence select a portal frame timber size of 110 x 533
The self weight of the portal frame was then added into the data, giving a new bending moment.
142 KNm > 135 KNm
198.7 KNm > 191 KNm
We can therefore assume that the member of glulam 17 - 500 x 110 is structurally adequate for the portal frame
7.0 Joint Design
Knee Joint Gusset:
Using another engineering program ‘nailgrp’ the amount of nails and hoops required to overcome the moment capacities was determined by inputting the length, depth and slenderness coefficients. As the moment obtained was 191KNm, 312 nails and 6 hoops were needed.
For more details of the gusset calculations, see the Connection Calculation Appem
Ridge Joint:
The ridge joint is simply a bolted pin joint, designed in accordance with AS1720.1 Section 4.4 "Design of Bolted Joints". Equation 4.4(3) was used to ensure that the capacity of the joint resisting lateral loads in shear was sufficient to withstand the applied load. The following table summarises the results.
8. End Walls and Mullions
The mullions are the vertical members that support the end wall sheeting rails. The mullions only need to resist horizontal wind loads and are subjected to bending moments. In the design, the mullions were spaced five metres apart, and their size depended on the maximum bending moment.
The mullions were designed to resist a series of point loads applied by the sheeting rails. The loads applied to the sheeting rails were calculated in the wind load calculations. For simplicity of design and construction, all mullions were designed a constant size. To ensure the mullions were structurally adequate, the mullion with the most extreme load cases was considered, this being the middle mullion. All mullions were assumed to have a pinned connection to the footing.
The chosen member for the mullions was 300 X 85 GL17. This member meets both
deflection and bending strength requirements.
For detail calculation refer to Appendix.
9.0 Conclusion
The report verifies that the design of the industrial warehouse structure is stable under all possible combinations of applied loads. The design features of the construction were complied with the Australian standards 1170.1, 1170.2 and 1720.1. The structure was calculated to withstand dead, live and maximum wind loads. The members chosen for each segment of the structure are listed in the table below. Each member has been tested against the engineering requirements regarding the load applied directly to it.
Roof metal sheeting: Lysaght Klip-Lok 406 0.48mm
Wall metal sheeting: Lysaght Klip-Lok 406 0.42mm
Purlins: GL17 267mm x 110mm
Girts for all walls : GL17 233mm x 110mm
Portal Frame: GL13 533mm x 110mm
Mullions: GL17 300mmx 85mm
Gusset Plywood F27 L=700mm D=600mm change* TIM
Ridse Plvwood F27 L=700mm D=600mm
10.0 References
- Miller and Crozier, 2000. Structural design of Timber portal frame buildings. National library of Australia cataloguing- in- publication entry, Australia
- CIV2224 – Timber and masonry structures, lecturer and tutor consultation
- Australian Standards for Civil Engineering Students HB 2.2
