certain buildings to collapse."
He went into a lot of detail about vertical and horizontal movement, and
about the frequency or the ground movement and the frequency at which
the building vibrates at.
Kit Miyamoto told us about a line of buildings they examined in China.
All built to identical standards. Most were damaged, some seriously, but
two collapsed (not adjacent). It's hard to know why those particular
buildings responded differently.
Even when destruction is severe, a building can still be restored and
rebuilt to 100% of the current building code. Do you want too?
Performance based engineering is physics based. It can be relied on.
Building codes, in contrast, change every 5 years or so and represent a
moving target. Building heights are not problematic in earthquake-prone
areas. My company retrofitted a tall building, designed in 1910, and by
installing base isolators and some internal bracing, we were able to
bring the building up to 100% modern standards. It's possible to do a
great deal to protect existing buildings.
Global Risk Miyamoto, assesses the risk for existing buildings.
All concrete buildings built prior to 1980 are potential death traps.
However, they can be protected.
The problem has been demonstrated in Christchurch, but the critical
place for immediate action is clearly Wellington.
These are your options:
1) Do nothing.
2) Buy insurance.
3) Employ engineering solutions.
In New Zealand because insurance has been so cheap, building owners have
made the choice to buy insurance.
It is possible to restore heritage buildings, but banks, insurance
companies, and engineers can all influence the decision.
Insurance in New Zealand is cheap, so almost everyone was insured.
That's unusual internationally. The easy availability of insurance has
in fact caused some problems, especially for the city as a whole.
Because insurance was cheap, there has been a lack of engineering
analysis, and reluctance to invest in structural solutions. For
instance, there was (at least some) knowledge that the CTV building was
dangerous. (If insurance here was more expensive and more conditional on
building structure, that collapse might have been avoided.)
The availability of insurance protects the building owner. He or she can
turn the disaster into cash and walk away. If that investment leaves the
city, it's going to be difficult to replace that money, and to put a new
building in that place. This is one reason why a quick rebuild is
desirable. Money won't lie idle.
If you expect to live with 100% safety, you can't live anywhere on
earth. I Japan we don't have the option of leaving vacant earthquake
damaged land. We would not abandon the red-zone in Eastern Christchurch.
There are relatively inexpensive methods to re-level houses and to
restore broken houses.
There is always a lack of money. We cannot fix everything; so choices
must be made.
What buildings should be protected? You protect buildings with a lot of
people in them. You protect buildings that are historically important.
You protect buildings essential the maintenance of services in an
emergency, the emergency centre HQ, the hospital, some schools, or
community centres.