Civil Engineering Reference
In-Depth Information
Figure 14.13
STAR: detail of prestressing duct (Photo: Benaim)
14.3.11 The daily cycle
A typical casting cell can be expected to produce one segment per day, which, when
taking into account the learning curve, maintenance of the mould and statutory
holidays, yields on average about 5.3 segments per six-day week, with both casting
and maintenance on the sixth day, about 270 segments per year, or 4.7 segments a
week for fi ve days casting and maintenance on the sixth day.
Achieving this daily cycle ensures that the process is truly industrial, with an
organised and repetitive daily and weekly routine. Experience shows that where this
daily cycle has been achieved, production costs are lower and quality higher.
For normal segments, weighing up to 100 tons, there is no reason not to achieve
the daily routine. For exceptionally large or complex segments, it may prove more
diffi cult. If such segments make up the majority of the length of the deck, additional
measures, such as the secondary precasting of the bottom slab or webs should be
considered. If they are only occasional, then it is necessary to fi nd an organised way
of introducing this disruption into the industrial process. For instance, where complex
and heavy pier units are used as the origin of casting runs, they may be cast in a
separate, non-mechanical mould, off the critical path.
It is normal for there to be a learning curve while the construction team debugs the
equipment, learns the best methods of assembling the reinforcing cage and fi nds how
best to fi ll the mould. The length of this learning curve generally refl ects the degree
of preparation and preplanning by the contractor. The daily cycle should be attained
after about 15-20 segments. A typical learning curve for a six-day casting week would
be as follows:
