Civil Engineering Reference
In-Depth Information
Costs estimation higher than expected: cut-back
In the autumn of 1998, the contracting combination provided an indicative
costs estimate for the suspended and protecting structure. The estimate
was much higher than expected, particularly because a much heavier struc-
ture appeared to be necessary than was initially presumed. In order to keep
the costs low, it was decided to cut back on the protecting structure around
the cables. Naturally this solution had to be tested regarding the require-
ments in the field of safety and in light of this, it was decided to carry out a
risk analysis.
Suspended structure is inadequate
The investigation soon proved that the solution used until then, which
involved a protecting structure would have been inadequate, certainly in
case of a fire.The protecting structure had been designed in the same man-
ner as the suspended structure: if the suspended structure failed, the pro-
tecting structure would also collapse. Besides, it appeared that when only
one or some of the brackets with which the cables were suspended would
fail, it would result in a domino effect: the cables would fall down over a
very long distance. It was clear that a renewed basic design was needed and
the contracting combination set to work on it.
Induction voltage and electro-magnetic fields: extra facilities
necessary
In November of 1999, the contractor provided a quotation for the solution
which was accepted by the client, for the suspension of the 150 kV cables
without protecting structure. However, the price was still much higher than
the available budget. The contractor also provided a separate quotation for
the protection of the electrical and mechanical facilities against induction
voltage and electro-magnetic fields. Besides, the designed stops (steel cabi-
nets) which had to prevent the cables from falling down over a long distance,
had to be provided with heat-resistant material.They would otherwise, in case
of fire, create a 'heat bridge' towards to concrete wall and could cause spalling
towards the concrete. These complications caused a major difference in the
client's estimate.
High-voltage cable expunged
Due to the fact that, in view of the implementation planning of the entire pro-
ject, the implementation would have to commence before the summer of 2000,
not enough time remained to choose a new technical solution: the housing of
the 150 kV cable connection was expunged. This resulted in the ending of a
nine year period of research, designs and consultation since the technical limit-
ing conditions were formulated.The moral of the story:There was much more
at hand than initially could have been estimated, even by experts. Working
with high-voltage cabling is extremely specialized work. It is therefore import-
ant to chart all the relevant aspects (such as heat development, influence of
magnetic fields, suspension and suchlike) and their associated costs, at a very
early stage. If that does not happen, then the danger exists that the one sub-
optimum design replaces the other.
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