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Loss of Rebar productivity - Change in density per

9 replies [Last post]
Wed, 2005-07-06 07:01
N.M.Raj Nadarajan
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Hi...

I would appreciate it if someone could point me in the right direction.

I am trying to find some literature/norms/studies which could provide details on the loss of productivity (Man hrs/ton) that takes place when the density of rebar is increased per cu.m of concrete. Obviously, the dia. of the rebar remains the same.

Best Regards,

Raj
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Replies

Wed, 2005-09-28 02:41
#1
Clive Randall
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There are so many factors that affect the fixing rate of rebar. I very much doubt if you will find a study of exactly what you want.

The question however is what are you trying to prove. I assume that it is you allowed $X per tonne for fixing rebar based on the production of rebar fixers.

Due to the increased complexity complexity ie number of layers number of links etc etc caused by the concrete to rebar ratio increasing the fixing time increased and therefore the rate should be increased. This is really hard to prove and can probably only be done by looking at the labour employed for this project as against the normal fixing rate in your locale.

However you may be wanting to prove that becasue of the number of layers the time to fix beams and slabs was increased and therefore there was a delay this is far easier to prove.

To be of any assistance, I feel what you are trying to prove and why needs explaining. Then maybe all the guys can give you some devious ways of proving your case
Hope this helps.
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Fri, 2005-09-09 07:44
#2
Katalin Hovanyi
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Haliho,
One thing the increased quantity other the design change. Once I was in similar situation. Recalculated a lot of things for the more or less 2 times as much rebar, I got 1.5 times much resource requirement and lost nearly a month because the design institute didn’t change the anchor design and simple there wasn’t enough place to put the anchors in. So the calculation and the formulas one thing and the real life is another.
Regards
Katalin
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Tue, 2005-08-09 08:41
#3
Charleston-Joseph...
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hi,

Look for some John Paige estimating handbook.

regards
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Fri, 2005-08-05 11:14
#4
John Herbert
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assuming you have already submitted rebar rates, I agree with zhang your adjustment should focus on the increased tonnage.
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Fri, 2005-07-08 00:30
#5
Zhang Haixiang
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Hi Raj,

First, the productivity is a rate (x ton/man.hour). increasing the density may increase the difficulty of installation, that will cause the loss of productivity, but not so much

For typical beam/slab, the desity of rebar should be within a certain range specified by design code to ensure the strength of the structure and also easy to construct. I don’t think there will be a significant loss of productivity if the density is within a reasonable range.

I think the key problem is the quantity increased greatly (3 times), so you need more time or resources.

I suppose you focus on quantity rather than productivity
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Thu, 2005-07-07 01:45
#6
N.M.Raj Nadarajan
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Hi All,

Let me try to answer all your queries:

1. Firstly, we did not have any typical rebar details in the Contract; it was a provisional item. However, an indicative tonnage per cu.m was included in the BoQ to aid tenderers.

2. The actual density on site is almost 3 times more (Beams & slabs). As Alex wrote earlier, this has also resulted in an increase in complexity…ergo loss in productivity. I am aware that the density could increase by simply increasing the size of the rebar and that this would, in fact, result in improved productivity. However, my question is related to loss of productivity due increase in density ( and complexity) with no change in rebar diameters i.e. only the number of bars have been increased.

3. Now, the question is this…is there any literature/norms/studies which would help me to get an idea of the loss in productivity due to this increased density/complexity?

4. I cannot rely on site data as I don’t have anything to compare the on-site productivity to…!!

Thanks for your input guys…

Regards,

Raj
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Thu, 2005-07-07 00:30
#7
Sunil Kumar
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Hellow Raj,

As Alex say there would an increse in rebar which will increase the manpower requirement. Then increase in Rebar / rebar per person will give you total mandays required to do the job...

Trsut this should suffice

Sunil
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Thu, 2005-07-07 00:13
#8
Alex Wong
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Raj

Instead of man hours loss in productivity, how about man hours increase due to, increase complexity, increase number of rebars, more difficult to access and number of cycles increase.

Cheers

ALex
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Wed, 2005-07-06 23:54
#9
Zhang Haixiang
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Hi,

could you first explain, why there is a loss of productivity when the desity of rebar increase.
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