...Structural Engineering, amongst many other things, is about balancing risk with cost. We do not design buildings to be invincible. We set limits....
I haven't been game - bold enough - to go there - other than mentioning "risk management". I emphasised these two in my explanation challenge for Sander.
1) Protect the people first << I said explicitly
2) Protect the building second << I said explicitly
I did not address
3) Improve US codes for resistance to progression
And the one which would probably be too hot to handle:
4) The policy decision - at both Government level AND Building developer industry level - will almost certainly be:
(i) Improve preventive security BUT
(ii) Ultimately "wear the risk".
... For example, we design buildings for design seismic and wind events that do not correspond with theoretical maximums....
Known territory for civil engineers. The other members may be interested in a couple of related examples which are "non-structural". (Well - not high rise building structures for the first one.)
The world wide example where we (Engineering profession) have over the last 40+ years tried to design for "theoretical maximums" is in large dam design. The current "PMP - PMF" (Possible maximum precipitation - probable maximum flood [resulting from it]) design standard is as close to "design for worst case" as I am aware of. For the non-engineers - the old standard was usually "design for the 1 in 1000 year flood" - roughly explained as "for a 50 year old dam you have already taken a 1:20 risk" (Statistics pedants - yes I know but it is good enough to make the point simply.
) Most of them built after mid-late 1800's and by 1930s - 50s quite a few were falling down - natural forces of hydrology - not those due to military action. So many large dams have been reassessed and reinforced. All seven of those serving Sydney.
...we don't want to do it. And that's okay.
That is the policy aspect I didn't want to raise...high risk of derail.
When "we" upgraded the Sydney Water Supply treatment processes ( my last big project in that job - 1989 onwards) the economists first round risk management calculations were in terms of "deaths per million customers from water supply contamination".
None of us wanted that discussion "out there".
Ditto few would want to make a lot of noise over the realities of economic design of high rise buildings at the limits.
AND that was the unstated underpinning reason why I was so emphatic with Sander. The ultimate priority in the event of fire or major damage in a high rise building will remain as "get the people out". Because ultimately we cannot afford to protect the building at the extreme limits. So a "risk managed" decision with a limit.
)
