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RE: seaint Digest for 2 Aug 2008

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Akbar,

 

Politics on condition it has a structural bias. And design is political. The acceptable level of performance for all structures in all nations is a consequence of subjective opinion, and not science. What opinion becomes a mandatory requirement in a code of practice is a consequence of political debate and action by the members of the governing committees. Economics and scarcity of resources also has a large influence, as does the risk of loss of amenity and the insurance industries or government’s capacity to replace versus the hazard to life. For the most part the magnitude of design loads are a consequence of loss of amenity and capacity to replace and have very little to do with hazard to life. The risk to life is best tackled by avoiding the hazard, rather than providing high resistance.

 

Harold and Andrew had interesting points on the issue.

 

I would like to know how many stress cycles have been experienced during the LA earthquake and consequently what the remaining fatigue life of the structures are. Since convincing the public that structural engineers can make it safe to live on the edge of a fault line, actually does deserve lawyers throwing everything they can at structural engineers. As does convincing them that it is save in the path of a hurricane, tornado or tsunami.

 

Are buildings pushed up high because of scarcity of land or because of profit motive? Just because something is possible doesn’t mean that it should be made common place. Having the world’s tallest building is political. Having 2 tonne of steel to build a frame versus only having half a tonne is political.

 

Engineering is fundamentally about maximising the benefit from available but otherwise limited resources.

 

Structural engineering is thus political, since it involves meeting human needs for shelter and other structures from limited resources. Those needs have to be met by balancing a multitude of conflicting needs.  The definition of who or what is an engineer, and who can practice engineering is also political. This in itself can create an unwarranted scarcity of resources in the form of availability of engineers. It can waste time teaching people a great deal about very little of practical value. It can push up the price of housing and cause delays in the supply of housing whilst some engineer plays games with numbers, for what a 100 years of history has demonstrated to be more than acceptable. Not because of real risk and hazard, but perceived risk. Also more risk to the engineers insurance due to being over confident about what they can supply, then being taken to task by lawyers when the engineers structures fail to live up to the expectations which they have promoted.

 

Life is political. And engineers have to operate in a political environment, but much of what they don’t like about it is of their own making. Hence Bill’s original objection to politicians getting all the credit. But whilst the LA buildings may have faired well this time, fatigue is accumulative so how well will they fair next time? When they fail the credit will pass to the engineers.

 

But who told the politicians the buildings were “safe”? Who is it that applies design factors and declares structures to be 67% (1/0.6) stronger than required? Who is it that thinks they know what the design load should be, and what the actual resistance of the structure is? Engineers?

 

It is political!

 

Regards

Conrad Harrison

B.Tech (mfg & mech), MIIE, gradTIEAust

mailto:sch.tectonic(--nospam--at)bigpond.com

Adelaide

South Australia