I was under the impression that if someone with knowledge of engineering
science is involved with a project, and they use a prescriptive solution and
that solution fails. Then if engineering science can be taken as predicting
such failure is likely, then the person would be held accountable.
Constraints on prescriptive solutions are generally tightened after a
failure, not before. Because the historical evidence supports the
prescription. Just like all the evidence indicates all swans a white, unless
visit Australia and acquire new evidence that swans can be black. Supporting
evidence is not good science if counter evidence is not sought.
If the builder follows the prescriptive solution, then they may be covered,
but if the engineer blindly accepts the prescriptive solution then they are
unlikely to be covered, because the engineer can make a technical assessment
of the solution. A coroner may find the engineers acceptance of the
prescription negligent.
Also arguing one code against another won't get any where. There has to be a
more rational basis for the 18" maximum, than the code says so.
The whole point of engineering science is to get beyond arbitrary
prescriptions: so that can innovate and also avoid predictable failures.
If builders and owners want to go with prescriptive solutions then no need
for an engineer. If they ask an engineer, and want the engineer to take
responsibility, then they have to accept the judgement of the engineer. Or
go with the prescription and accept responsibility themselves.
There is no such thing as over engineering. Things are over sized due to a
lack of engineering, and under sized due to a lack of engineering. An
optimum solution achieves the maximum benefit (added value) from the
available but otherwise limited resources, with an associated acceptable
level of risk.
The calculated solution should have a lower risk of failure than the
arbitrary prescriptive solution. Depending on your loading code, you can
estimate that higher risk.
Do the owners want to accept the higher risk of loosing their fancy kitchens
and bathrooms? Do they want to shift some of their limited resources into
the structural resistance and keep the benefit of the kitchen for longer?
For most people the added value, Andrew was talking about, is the utility of
the space, the proximity to shops and schools, and the view from the window.
Such things are always present and apparent when selling an established
house or other building. But concrete in ground is hidden, as is reo in the
walls. If have two identical houses, on adjacent blocks, and the property
boundary also marks boundary between reactive soils and stable soils. Then
the extra cost of the footings for the house on the reactive soils, will not
be recovered at sale: the perceived value of the two buildings will only be
based on the utility of the buildings. It is the designers task to
distribute the costs in the building on the reactive soils, such that the
perceived value of the building is greater than the cost. {Aware that Gil
will tell me 2+2=4 not 3 or 5. The subtlety is knowing what is being added
and subtracted.} A starting point would be to make the two houses distinctly
different.
In the current situation the difference in cost between two identical
buildings, would only be the difference in cost of reo and its installation,
the increased value in terms of resistance would not be perceived by future
buyers. Likewise the cost of temporary formwork, and props and bracing and
labour involved is added cost not added value, and difficult to recover on
sale: the ICF is meant to reduce such costs and reduce over all construction
time. The number of bars used should meet the requirements of the structure
and capabilities of the ICF. The number of bars shouldn't really be a cost
issue because that is offset by the labour savings elsewhere, unless the ICF
cannot accommodate more bars. Force a more detailed analysis of costs to be
carried out, assessed against the suppliers perceived value of their work.
Get the extra bars added without any increase in cost. Have the supplier
demonstrate the real benefit of their technology.
Alternatively if calculations do not refute the 24" prescription and the 18"
is just as arbitrary as any other prescription, and the building is a small
addition, then the risk of accepting the 24" doesn't seem too great. But it
does suggest identifying why the 18" constraint?
Though as Andrew suggests the benefit of sticking with 18" is potentially
greater than the cost: though if polystyrene forms the exterior surface may
not be all that relevant. The problem is explaining any benefit to the
owners, so that they can put a dollar value on it, if they need to.
The successful producer of an article sells it for more than it cost him to
make, and that's profit. But the customer buys it only because it is worth
more to him than he pays for it, and that's his profit. No one can long make
a profit producing anything unless the customer makes a profit using it.
[Samuel B. Pettengill]
Regards
Conrad Harrison
B.Tech (mfg & mech), MIIE, gradTIEAust
mailto:sch.tectonic@bigpond.com
Adelaide
South Australia
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