Holdfast Training Services Trial Blog

Today I have spent the vast majority of the day designing a bit of scaffolding.  The scaffold will be used to attach a “Considerate Contractors” banner so that it can be viewed from the neighbouring railway station platform.  It would be particularly embarrassing if millions of pounds worth of disruption to the railway was caused because a “Considerate Contractors” banner blew off it’s support and landed on the tracks.  So no pressure then!

I started by considering the forces involved.  Essentially the scaffold is required to hold the banner in place against wind loading, at which point I groaned at the thought and opened EC1 and the NA.  After considering the elevation, distance in land, urban environment and all those other factors I hoped I’d never need again I then stumbled onto the clause regarding signs.  Clause 7.4.3 gives you a coefficient to use when designing signs and the like.  When applied alongside the seasonal factor for the length of time it will be in place it gave me a total wind load of 0.853 kN/m2.  I checked it with Sam (our resident CEng) who said it seemed about right but that he’d never designed anything to EuroCode in his life.

My next step was to ensure that we could connect it to the scaffold.  So I fell back on a skill I honed in Exercise Rhubarb Creek: I googled it.  A 3M (TM) “Standard” Cable Tie has a breaking strain of 220N.  I did a quick bit of maths and found that one tie would hold down a banner 190 metres long.  Then I noticed it was in N not kN.  So I had another go.  190mm, that’s more like it.  The banner has holes every 450mm, so I needed to go bigger.  A “Light Heavy Duty” Cable Tie has a breaking tension of 530 N.  Each pair will support 460mm, so a tie top and bottom through each hole will hold it back.

Next came the scaffold itself.  I decided on a horizontal bar top and bottom of the banner attached to 4 vertical bars at 2 metre centres.  I tried desperately to work out the friction from a screw jack, but to no avail.  So instead I just specified that each jack should be bolted to the slab/soffit and specified a bolt using the manufacturer’s data.

And there we have it.  I’ve designed some scaffolding!  They’re going to build it next week, I really hope it doesn’t blow away!