During the design phase of a structure, there are certain loading conditions that engineers need to take into consideration. One of those loading conditions is seismic load, which is a dynamic load caused by the acceleration of the earth supporting the structure. Earthquakes can occur in any location at any time with increased activity near known fault lines. In fact, the Western New York area is located near a fault line, The Clarendon-Linden fault. This fault line is not expected to produce a major earthquake event; therefore, the area is generally considered a low seismic area.
Engineers use performance-based design to determine the seismic forces that would be applied externally to a structure and compare that load to other dynamic loads, such as wind forces. Performance based design requires structures to perform based on its purpose, occupants, location, and soil characteristics underneath. Engineers will look at ground motion response acceleration maps as part of the seismic load calculation. Seismic design is required for most designs, and there are very few exceptions in the International Building Code. Sometimes these exceptions in the code are overridden by state and local code requirements.
Building materials with high ductility such as steel and wood are often used to resist seismic forces. Ductile materials allow a structure to flex, absorbing and dissipating energy when subjected to sudden earthquake forces. Brick and concrete structures can be designed to resists seismic forces. However, ductility needs to be built into those structural systems. This is typically done with steel reinforcement.
Certain areas of the world require more consideration for seismic design. Higher seismic areas, such as the West Coast of the United States, require structural systems and connections to be seismically qualified. It is very important for an engineer to select a structural system that makes efficient and economic use of the materials chosen to keep the risks at a minimum.
If you or your company has any need for or questions about seismic design, contact Senior Structural Engineer Daniel Sarata at [email protected] or (716) 592-3980 ext 138.