Earthquake Resistant Architecture
Earthquake Engineering or Seismic Retrofitting is the construction or modification of buildings that are more resistant to seismic activity, soil failure, and ground motion.
Levels of Modification
- The goal is to protect human life, ensuring that the structure will not collapse, and that it can be safely exited. Under severe seismic conditions the structure may require tear-down and replacement.
- The structure, while remaining safe for exit, may require extensive repair (but not replacement) before it is considered safe for occupation. This is typically the lowest level of retrofit applied to bridges.
- The general structure is undamaged and undiminished in use for its primary applications. Any required repairs are only “cosmetic”. For example, minor cracks in plaster, drywall and stucco. This is the minimum acceptable level of retrofit for hospitals.
The most common structures requiring earthquake engineering are bridges, dams, road viaducts, towers, unreinforced masonry and insufficiently enforced concrete structures. Low rise buildings (around ten stories high) are relatively stiff and light and so have a higher resonant frequency while higher buildings will usually incorporate ductile steel frames and by their height will have lower natural frequencies.
By constructing a building following the building codes designed on the basis of the seismic history of the region, the extent of damage can be greatly reduced. Some prominent structures that suffered little to no damage in earthquakes have been based on earthquake engineering.
California falls in a highly seismic region in the west coast of the U.S. In October 1989, a high magnitude quake struck the Santa Cruz Mountains in central California. The 49-story office building shook for more than a minute. However, no one was seriously injured, and the Transamerica Pyramid was not damaged. This famous San Francisco landmark had been designed to withstand even greater earthquake stresses.
The 1994 Northridge earthquake cracked the surface pavement on the upstream slope of the Los Angeles Dam. Overall, the dam, designed to withstand severe shaking, suffered very little damage.
- A complete probabilistic analysis and design approach
- Performance-based design codes
- Multiple annual probability hazard maps
- New structural systems and devices using non-traditional civil engineering materials and techniques
- New analytical tools for reliable prediction of structural response
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