# Acrow prop specs

#### Norcon

The most amusing has been you googling "newtons" and then submitting the wrong info to the forum.

#### iandandav

You are wrong about the part highlighted in bold if the load is vertical down.
I a not wrong because I said 'if they were tilted' NOT vertical. Please read the posts CAREFULLY before replying as its makes you sound like a silly billy
edit
even if it was vertical then the rules would still be the same except the horizontal force would be zero.

Oh and btw. You never ever tilt an acrow prop unless absolutely necessary.

?? At what point did I say they will be tilted. I was using that as an example too explain some school boy physics to you.

#### iandandav

Iandandav, people here are trying to help you, but you are making it very difficult for them...

You said "The spacing can't be deduced until the number of props has been determined."
However, this doesn't take into account that, for example, you may only need one prop for the applied load. However, you know very well you would need more than one prop.
So you can determine a minimum number of props for the load, but it won't necessarily be enough. One prop on a five metre span will not hold up the back of your house, regardless of the load applied. You also aren't going to want to space them at more than about 900mm or so, otherwise the brickwork will not arch between them. This is why spacing is also important.

If you use Strongboys and prop from one side only the capacity is greatly reduced due to the cantilever effect of the load applying a moment to the prop.

Im not, and havent at any point disputed any of this. Please reread the previous posts and the original question.

Finally, you are almost correct when you talk about props at an angle. There will be a horizontal and vertical component, but they are not additive. Forces are vector quantities, so, you use trigonometry or pythagoras to calculate the resultant force.

For example hyp = sqrt (opp² + adj²)
[/quote]

Yes I know you use trig to calc inclined forces. I was trying to keep things simple for Norcon

#### Norcon

But if the acrow is tilted the mass remains the same but the force splits into two components, a vertical and horizontal both less than the original but adding up to the original. The vertical now becomes less, this is why force is used in these calculations instead of mass

I can assure you thats wrong.
When you tilt the acrow the force on the acrow will be greater than the original downwards force.

Its the same when the force is horizontal.
If you have two acrows beside each other and one is tilted and the other horizontal, the tilted acrow will fail first.
The force multiplies the more you tilt.

I've seen this a thousand times. I've watched props go banana many times.
Pouring wet concrete against them is the ultimate test.

You said the load was 10 ton in the opening post. I gave you the answer to that.
12 standard props extended to 2.5m.

You would be a real asset out on a civils building site.
Making the tea and brushing up.

#### DIYnot Local

Staff member

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