Any QS's/Estimators out there? Nelp needed

[MrBump]

I'm currently doing an HNC in Quantity Surveying and have a question in an estimating tutorial that's really got me stumped as it really differs from the stuff we've covered to date. :confused:

Can anyone help me out calculating a pro rata rate for concrete??

[simonsheil]

Surely it is just a ratio of the data given?

Not a QS but work with them so if you post a copy I can ask tomorrow

[MrBump]

Brilliant, thanks!!

I've got the rate for a cubic metre of concrete using a 1:3:6 mix laid to a thickness of between 150 - 450mm.

The variation is to change the mix to a 1:2:4 mix with a thickness of <= 150mm.

Amending for the mix isn't an issue, i've done that plenty of times - but how do i take into account the decrease in labour output due to the reduced slab thickness?? The data sheet i've got states that placing a cubic metre of concrete 150 - 450mm thick takes hours 4 hours, but the same voume laid at 150mm takes 6 hours.

Any help would be great!!

[pdhealy]

I'm not sure if I've understood what you are looking for correctly. Are you looking to calculate the new rate per m3? Your labour costs per m3 have increased by 50% (6hr = 150% of 4Hr). Therefore if you know the labour cost for the m3 @ 150 - 450, then add 50% to it for <= 150.

HTH

[MrBump]

I'm not sure if I've understood what you are looking for correctly. Are you looking to calculate the new rate per m3? Your labour costs per m3 have increased by 50% (6hr = 150% of 4Hr). Therefore if you know the labour cost for the m3 @ 150 - 450, then add 50% to it for <= 150.

HTH

Why didn't i see that??? Nailed it, thanks!!!!!!

[KenONeill]

If I'm reading the question correctly it's nonsense. AIUI they're saying it takes 50% longer to pour a given area a 149mm than at 151mm thickness!

[sdenny]

If I'm reading the question correctly it's nonsense. AIUI they're saying it takes 50% longer to pour a given area a 149mm than at 151mm thickness!

They said the same volume laid at the different thickness, therefore the area would change.....

[KenONeill]

They said the same volume laid at the different thickness, therefore the area would change.....

I misread the datasheet then; mind you I still think that the smoothing time per unit volume will be a linear function of thickness (since area covered per unit volume is an inverse linear function of thickness), rather than a step function.

[duke of hazzard]

this is a joke, im a qs and the amount of time they spend teaching you this could be spent on teaching you something usefull like cad measurement.

[KenONeill]

Contrarywise; if you don't understand the principles, how can you tell when your computery measures are talking hallibut?

Case in point. QS and I were measuring the office using a laser rule. Looked at result and said "That's not right; it's about 1/3 more than that." Cutting a long story short, it turned out we were measuring a return off a ruler in someone's desk tidy.

[sdenny]

I misread the datasheet then; mind you I still think that the smoothing time per unit volume will be a linear function of thickness (since area covered per unit volume is an inverse linear function of thickness), rather than a step function.

I agree, but I guess it's just easier that way

[pdhealy]

this is a joke, im a qs and the amount of time they spend teaching you this could be spent on teaching you something usefull like cad measurement.

I guess they are trying to give the student QS the "tools" to hack variation rates of greedy groundworks subbies