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<b>Hook time for precast or structural steel</b>

6 replies [Last post]
Sat, 2005-04-30 05:33
Roger Herod
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We are trying to conduct a detailed analysis of the "piece rate" for a structure in a high rise office block (60 storeys). The objective is to determine whether a four day construction period per floor is achievable; we know its possible using post tensioned flat slab, but the engineer has designed a precast solution that we fear can’t be done - certainly as we go higher up and the hoisting/lowering time starts to dominate the overal cycle time the "piece rate" will fall.

Does anyone have or can point me to a detailed breakdown of a typical cycle. Precast components may weigh upto 16 tonnes and the crane we’ll be using is a 380 tonne metre luffing tower crane fitted with a 40 metre jib.

Many thanks to anyone who can help
Roger Herod
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Wed, 2005-05-04 21:21
#1
Roger Herod
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Phillip,

Many thanks for your help. I will discuss with my colleagues and get the study under way.

Roger
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Wed, 2005-05-04 05:57
#2
Philip Jonker
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Hi Roger,

The largest amount of hook time is normally taken up by placement of the item (Steelwork/Precast) ie the time taken up by positioning and fixing in place, as well as the rigging time. The time to actually lift and lower the items is a small portion of the total hook time, and can be calculated for the average height of the structure. The will obviously be dependant on the configuration of the crane. Another factor is the complexity of the rigging. The amount of required for placement is dependant on the complexity of the structure, the size of the elements etc. In typical steel structures the rule of thumb is to allow an average of 30 minutes per piece. This is also dependant on the weather, factors such as rain, mist and wind, will affect this duration, so it is important to look at the weather condition in the area where the structure is to be erected.
There is obviously ways to reduce the lifting times, like pre-assembling steelwork on the ground or ensuring more rigging tackle is available so the crane spends less time waiting for rigging-up.
I suggest that you get a rigging study done which will help you to assess the required time. To give a simple answer to what sounds like a complicated problem is not easy.

Regards

Philip
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Tue, 2005-05-03 21:42
#3
Roger Herod
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Alan Chadwick,

Thanks for your post. Yes the building has a core and we’re currently studying the formwork system that may be employed.

What I’m really looking for is detailed information on the amount of time the cranes will be occupied erecting structural steel or precast concrete, on a piece by piece basis. We can then factor in the hook time for the core system once the method has been decided.

Regards,


Roger Herod
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Tue, 2005-05-03 21:37
#4
Roger Herod
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Alex,

Thanks. I’ll take your advice.

Regards,

Roger Herod
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Tue, 2005-05-03 20:02
#5
Alex Wong
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Roger

A good friend of mine might able to help you. He also working in the region. You can send him private message though PP since he is one of the member in PP. His name is
Ron Brinkman. Send him a message or if you have difficult to locate him - send me a private message and I will forward his details to you.

All the best

Regards

Alex
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Tue, 2005-05-03 07:50
#6
Alan Chadwick
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Roger,

We had similar problems when we built the main towers on Tsing ma bridge....in the first instance i assume that there is a central core going in advance of the decks ...how are you proposing to build the central core.

Will you be using slipform or jump form, if using jump form will it be self propelled...i.e will not require hook time ?
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