Suspended concrete slab-HOW MANY PROPS TO HIRE/

[gnvqsos]

I need to hire some props to support three sections of 19m ply to hold approx a cubic metre of concrete.The ply sections will be 8 X 4 ,8 X4 and 3 X4.I have some 4X2 timbers to support the plywood.How many props should I hire.I was considering ten but I might be overdoing it.

 

[alfiembra]

A cubic metre of concrete weighs 2400kg or 2.4 tonnes so check what the capacity of the props are and give yourself a factor of safety of at least 2:1 so if you calculate for example that 3 props are adequate hire six. Also consider some scaffold tubes to rig up cross bracing between the props to make them more stable. Also consider what you are propping off, is it a suspended floor in which case you might need to "through prop" i.e prop the floor your propping off.

HTH

Alan

 

[JerryM]

you've probably started the work so input may be too late.

i was interested as my initial gut feeling was 19mm seemed too thin to support anything.

i back calculated that the thickness of concrete is 140mm which equates to 13 off 25kg bags on each sq meter. this again seemed a lot.

i am no expert on structural calcs but a quick approximation of a simply supported rectangular plate without factor of safety suggests ok (deflection <1mm) with 4 props under each sheet ie 12 in total.

If you’ve got any 25 bags handy it might be worth as precaution checking it to confirm all ok before pouring,