Structural Design Of Buildings And Safety From Seismic Upheavals

Nature and Probability

Although seismic upheavals earthquakes cannot be prevented in practice, science and engineering provide tools that can be used to reduce their effects quite substantially. Firstly, science can now identify where and when earthquakes are likely to occur, at what magnitude and determine the relative likelihood of a range of ground shaking levels. This information is readily available to architects, engineers, code writers, planners and to the general public. Secondly, seismic researchers and structural engineers with experience in seismic design have sufficient understanding of the effects of earthquake shaking on buildings to create designs that will be safe for various intensities of shaking. Modern building codes incorporate all of this information and require buildings to have structural engineering designs appropriate for each region.

However, earthquakes are complex phenomena and the exact nature of ground shaking and a building’s response to that shaking, are still covered in considerable uncertainty.

Earthquakes: A Worldwide Problem

Most people now know that although most frequent in California and Alaska, earthquakes are not restricted to just a few areas in the United States. In fact, two of the greatest earthquakes in U.S. history occurred not in California. 37 of 50 USA States have regions with sufficient seismic risk and hence require structural engineering designs more stringent than the normal seismic zones. The likelihood of a damaging earthquake occurring west of the Rocky Mountains—and particularly in California, Alaska, Oregon and Utah—is much greater than it is in the East or South. However, the New Madrid and Charleston regions are subject to potentially more severe earthquakes, although with a lower probability, than most regions of the western United States. According to the IBC (International Building Code) structural design maps and the USGS (US Geological  Survey) hazard maps upon which they are based, other locations should also plan for intermediate ground motions.

Seismic Structural Engineering Design

Seismic design is highly developed, complex and strictly regulated by international codes and standards. Seismic codes present criteria for the design and construction of new structures subject to earthquake ground motions in order to minimize the hazard to life and to improve the capability of essential facilities to function after an earthquake. To these ends, current building codes provide the minimum requirements necessary for reasonable and prudent life safety.

Performance-based Seismic Structural Engineering Design Requirements:

- An engineering system for establishing the ground motion at given site based on seismic index and soil type
- Thorough seismic analysis of the existing building structure and systems
- Meticulous design requirements for building materials, systems and structure components
- Full description of irregular and asymmetrical building configurations and limitations on their use
- Building height limitations related to structural type and level of seismicity

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