Civil Engineering Reference
In-Depth Information
the exterior walls of buildings were often of brick, or in some cases hollow clay tile. Wood
was used to construct the roofs and floors, which were supported by the brick walls. This
type of construction was used for schools, and the destruction to these schools was some of
the most spectacular damage during the 1933 Long Beach earthquake. Fortunately, the
earthquake occurred after school hours, and a catastrophic loss of life was averted. However,
the destruction was so extensive and had such dire consequences that the California legisla-
ture passed the Field Law on April 10, 1933. This law required that all new public schools
be constructed so that they are highly resistant to earthquakes. The Field Law also required
that there be field supervision during the construction of schools.
2.
February 9, 1971, San Fernando earthquake in California:
Because of the dam-
age caused by this earthquake, building codes were strengthened, and the California legis-
lature passed the Alquist Priolo Special Studies Zone Act in 1972. The purpose of this act
is to prohibit the construction of structures for human occupancy across the traces of active
faults. The goal of this legislation is to mitigate the hazards caused by fault rupture.
There has also been a considerable amount of federal legislation in response to earth-
quake damage. For example, the Federal Emergency Management Agency (1994) states:
At the federal level, there are two important pieces of legislation relating to local seismic
hazard assessment. These are Public Law 93-288, amended in 1988 as the Stafford Act, which
establishes basic rules for federal disaster assistance and relief, and the Earthquake Hazards
Reduction Act of 1977, amended in 1990, which establishes the National Earthquake Hazards
Reduction Program (NEHRP).
The Stafford Act briefly mentions “construction and land use” as possible mitigation mea-
sures to be used after a disaster to forestall repetition of damage and destruction in subsequent
events. However, the final rules promulgated by the Federal Emergency Management Agency
(FEMA) to implement the Stafford Act (44 CFR Part 206, Subparts M and N) require post-dis-
aster state-local hazard mitigation plans to be prepared as a prerequisite for local governments
to receive disaster assistance funds to repair and restore damaged or destroyed public facilities.
Under the regulations implementing Sec. 409 of the Stafford Act, a city or county must adopt
a hazard mitigation plan acceptable to FEMA if it is to receive facilities restoration assistance
authorized under Sec. 406.
The overall purpose of the National Earthquake Hazards Reduction Act is to reduce risks
to life and property from earthquakes. This is to be carried out through activities such as: haz-
ard identification and vulnerability studies; development and dissemination of seismic design
and construction standards; development of an earthquake prediction capability; preparation of
national, state, and local plans for mitigation, preparedness, and response; conduct basic and
applied research into causes and implications of earthquake hazards; and, education of the pub-
lic about earthquakes. While this bears less directly on earthquake preparation for a particular
local government, much of the growing body of earthquake-related scientific and engineering
knowledge has been developed through NEHRP funded research, including this study.
14.1.2
Limitations of Building Codes
Common limitations of building codes are that they may not be up to date or may underes-
timate the potential for earthquake shaking at a particular area. In addition, the building
codes may not be technically sound, or they may contain loopholes that can be exploited
by developers. For example, in terms of the collapse of structures caused by the Chi-chi
earthquake in Taiwan on September 21, 1999, Hands (1999) states:
Why then were so many of these collapses occurring in 12-story buildings? Was it, as the
local media suggested, a result of seismic waves hitting just the right resonant frequency to take
