In part one of this series on making your own homemade scaffolding tower I discussed the research and design aspects of building the tower. In part two I perform a few quick calculations to prove the platform will be strong enough and put together a parts list for the material purchase.
Having worked with wood for about 20 years I was sure that my design was strong enough but I thought it wouldn’t hurt to do some calculations to make sure. The biggest unknown for me was the platform as I’d never really made a span before so decided to calculate for that. I figured it was approximately the same as the floor of a house so I used the same calculations an architect or engineer would. First though a few definitions:
- Joist spacing is the centre to centre distance of the joists (typically 400 or 450 mm centres).
- Span is the clear span between supports.
- Dead load is the joists, floor and screws.
- Imposed load is the person and any tools or materials.
Standard Floor Loading
Imposed loads should not exceed 1.5kN/m^2 for a regular floor (figures from BS6399-1, Current version is probably BS EN 1991-1-1:2002).
1 N = 1 kgm/s^2
Gravity (a) = 9.81 m/s^2
1500 = m * 9.81
m = 1500 / 9.81 = 152.9 kg
In other words 153kg evenly distributed over every square meter of floor.
The table below shows maximum spans (in meters) for C16 graded timber with the given centre spacing (columns)
|47 x 97||1.92||1.82||1.46|
|47 x 122||2.55||2.45||2.09|
|47 x 147||3.06||2.95||2.61|
|47 x 170||3.53||3.4||2.99|
|47 x 195||4.04||3.89||3.39|
|47 x 220||4.55||4.35||3.79|
- Width: 840mm
- Length: 1800mm
- Joists: 47×100 C16 on 450mm centres
- Span: 1500mm
The designed platform has a surface area of 1.5m^2 which gives a maximum loading of 1.5*152.9 = 229.3kg evenly distributed and assuming exactly the conditions given in the table. My platform however has a span of just 1500mm, significantly less than the maximum allowable span for C16 timber of 1820mm. Additionally I’ve assumed a centre spacing of 450mm which is true for the two centre beams but not the beams to either side which are more like 300mm centres. I’ll also be screwing down a single sheet of 18mm ply over the platform which is much stronger than floorboards. All things considered I would be happy saying the maximum safe load is 300kg, more than enough for me and my tools.
From the design I put together a list of parts and I then mapped that onto timber that I could actually buy. I shopped around online for the best price and got the whole lot delivered for £225. The tables below show the parts list and the timber I bought.
CLS Parts List
|Kickboard Long Support||50||50||100||4||400|
|Long Rail Stiffener||50||50||1700||2||3400|
|Rail Support Block Small||50||50||100||4||400|
|Rail Support Full||47||100||846||2||1692|
|Rail Long Stretcher||25||101||1800||2||3600|
|Rail Long Mid Stretcher||25||200||1800||2||3600|
|Timber Size||Total Length||Bought Length||Price||Cost|
Ply Parts List
All parts can be cut from a single sheet of 18mm ply costing £33.12.
|Cross Brace Gusset||18||225||240||2|
|Rail Short Stretcher||18||100||840||2|
|Rail Support Plate||18||100||151||4|
|M10 x100 Bolts||Main frame, guard rail||32|
|M10 Washers||Use thick repair washers||64|
|M10 Nylock Nuts||24|
|M10 Wing Nuts||Guard rail||8|
|M6 x 70 Bolts||Guard rail, platform locks||20|
|M6 Wing Nuts||20|
|M5 x 50 Bolts||Castor attachment||16|
|M5 Nylock Nuts||16|
|4 x 50 Wood Screws||Platform||30|
|4.5 x 70 Wood Screws||Rails||64|
|6 x 150 Wood Screws||32|
|Exterior Wood Glue||1000 ml||1|
|Heavy Duty Castor||60kg or greater||4|
|Bottle Jack||1 Ton or greater||1|
On to part three where I start the construction.