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Post Tensioned Slabs

4 replies [Last post]
Vrinda M
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Hello planners, Project is 5 star hotel resort.I have both post-tensioned,precast slabs in the building.Can anybody please tell me what are the activities involoved in the precast & post-tensioned slabs in a tender program.(Precast&post-tensioned-subcontracted).Also what is the productivity norm for excavation works?If excavation quantity is 14777m3 then approx how many days it will take? Thanks, Vrinda

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Anial Mak
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Once the concrete has gained strength but before the service loads are applied, the cables are pulled tight, or post tension tendon. Regular inspections are imperative to keeping the structure and the traveling public safe.

Alistair Blakey
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Joined: 20 Feb 2009
Posts: 6
Vrinda,

Don’t forget to allow at least 14 days curing between the casting and placing of the precast slabs. There may also be a grouting in activity after placement.

For post tensioned slabs you just need to allow a couple of days for post tensioning after the slab is cast. This will occur once the slab has reached a pre-requisite (e.g. 7 or 14 day) strength. The placement of the post tensioning cables can take place at the same time as the general reinforcement taking place.

As for the excavation, 14777m3 of excavation equals (possibly) about 20000m3 after bulking. If a truck takes 12m3 that means 1667 truckloads of earth moving. So you quantity depends on the number of diggers and trucks that you have, as well as how long it will take to get the earth to spoil.

Hope this helps
Alistair
Vrinda M
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Joined: 8 Jun 2008
Posts: 24
Thanks Neil for your info.

In normal in-situ slab we put Shuttering,Rebar,Concrete as the activities.I just wanted to know the activities involved in Precast Slab & Post-Tensioned Slabs.
As far as I know - Precast slab(Subcontracted)-activities are Design & Approval- 28 days,Material procurement & manufacture-30 days and thn placing of slab on site (1 day).Also since it is subcontracted we not received any quotation as yet.
but for post-tensioned slabs what is the sequence of activities I want to know?

Also for excavation project engineer had told norm 1000m3=12 days is this ok?if i dont have any information about no.of excavators etc.with your exp,what do you say how many days will it take for 14777m3 excavation???
At present i dont have any planner in my co.

if you can pls help.Any more info if you can share will be of great help.

Thanks,
Vrinda.
Neil Tait
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Joined: 31 Jan 2001
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Viranda,

I’d suggest:

Excavation - I could say 6 days or 300 days! What you need to look at is the layout and the constraints associated with the excavation, the necessity to complete the excavation in a oner, the links into and beyond the excavation (dewatering / temp works), ... Contraints may be trucks on / off site, available space to effectively operate x no. excavators, operating hours... This web site provides reasonable output rates for bulk excavation.

Precast - allow for adeqaute procurement (of S/C), shop drwgs, material / sample / method statement approvals, delivery... The actual installation is quick but allow dedicated access and resources - plan to avoid double handling. Ensure your casting schedule matches your construction schedule (casting of the easy big ticket items first may benefit the yard’s cash flow but not the programme).

Post tensioned - as per above... is it post tensioned pre-cast or in-situ? Allow for concrete to gain strength prior to tensioning activity (whats specified). Review necessary tensioning sequence as dictated by design - ensure this is reflected in programme... the list goes on.

If you have propspective SC’s (who are pricing for your tender submission) then speak with them as they are the experts and will tell you on what basis they have priced - ask for typical sequence. Check through contract / spec for associated requirements. Speak with those in your organisation who have experience or have been assigned to the tender...