Learning from Earthquakes - Earthquake Engineering for Structural Design - page 90

- In several countries and many cities in the world there are a lot of
buildings belonging to the cultural heritage, which are greatly exposed to
seismic hazard. The majority of these buildings are not engineered, so they
are lacking basic anti-seismic features and have never been fitted with
adequate provisions against earthquake actions. Due to this fact, many
historical monuments were damaged during the last strong earthquakes
(Fig. 3.18). It is a duty of specialists in structural restoration to develop
new methodologies to protect monumental constructions (Mazzolani,
2005, 2009).
- A great problem is the spreading of after-earthquake fires, mainly
produced by the damage of gas pipelines. The 1906 San Francisco and,
once more, the 1995 Kobe earthquakes, can be remembered like bad
examples, the after-earthquake fires producing more important damage
than from the earthquake itself (Fig. 3.19).
- Each area of potential disaster must have a regular road network with
many connections. Especially during the Italian earthquakes, great
problems arise due to very narrow streets (Fig. 3.20).
- It is required to assure the safety of engineering works such as bridges,
dams or others, whose collapse can have negative effects on the
performance of the urban systems during the seismic emergency. During
Loma Prieta, Kobe, Izmit and Taiwan earthquakes a lot of first importance
bridges collapsed, producing great difficulties in the accessibility to
damaged areas (Fig. 3.21).
In order to evaluate the economic consequences of large earthquakes, a benefit
for regional administrations and the owners is the availability of the data resulting
from some scenarios of previous similar earthquakes, which can be useful for
predicting appropriate measures to reduce the economical losses.
- A devastating earthquake is a relatively rare event and may occur once or
maximum two times during the building life. It is possible that such an
earthquake never affects the building. Therefore, in this case, according to
the design philosophy, the design requirements are less severe than the
largest possible ones and the structure is well prepared to support this
special situation without collapse, but suffering important damage.
- The very recent losses produced during the last earthquakes in structures
designed following the above design philosophy (especially in the cases of
Northridge and Kobe earthquakes) have shown that the financial cost of
the reestablishment of normal activity was so high that it was difficult to
bear even by rich countries.
- This situation has forced the specialists to develop a new design
philosophy, based on explicit and quantifiable performance criteria,
considering multiple performance and earthquake hazard levels for
earthquakes. The collapse of some poorly erected buildings and bridges,
the failure of some portion of life lines and the simulation of post-fires can
give a realistic idea about what can happen during a devastating
earthquake.