Lightweight construction with less mass is typically an advantage in seismic design. The greater the mass (weight of the building), the greater the internal inertial forces generated. Ground shaking (pushing back and forth, sideways, up and down) generates internal forces within buildings called the Inertial Force (F Inertial), which in turn causes most seismic damage.į Inertial = Mass (M) X Acceleration (A). The aforementioned seismic measures are used to calculate forces that earthquakes impose on buildings. Seismic Terminology (For definitions of terms used in this resource page, see Glossary of Seismic Terminology ) Earthquake damage will vary depending on distance from origin (or epicenter), local soil conditions, and the type of construction. Intensity is the amount of damage the earthquake causes locally, which can be characterized by the 12 level Modified Mercalli Scale (MM) where each level designates a certain amount of destruction correlated to ground acceleration. A building can withstand very high acceleration for a very short duration in proportion with damping measures incorporated in the structure. Usually, the longer the duration, the less acceleration the building can endure. If the level of acceleration is combined with duration, the power of destruction is defined. Moment Magnitude Scale is a recent measure that is becoming more frequently used. The Richter scale is based on the maximum amplitude of certain seismic waves, and seismologists estimate that each unit of the Richter scale is a 31 times increase of energy. Magnitude is the "size" of the earthquake, measured by the Richter scale, which ranges from 1-10.Duration is the length of time the shock cycles persists.Displacement is the distance from the point of rest, measured in centimeters.Velocity (or speed) is the rate of change of position, measured in centimeters per second.0.50g is very high but buildings can survive it if the duration is short and if the mass and configuration has enough damping.0.02 g or 20 cm/sec 2 causes people to lose their balance.0.001g or 1 cm/sec 2 is perceptible by people.Acceleration is the rate of change of speed, measured in "g"s at 980 cm/sec² or 1.00 g. ground motion), the following definitions are commonly used: In order to characterize or measure the effect of an earthquake on the ground (a.k.a. alone, the average direct cost of earthquake damage is estimated at $1 billion/year while indirect business losses are estimated to exceed $2 billion/year. DescriptionĪbout half of the states and territories in the United States-more than 109 million people and 4.3 million businesses-and most of the other populous regions of the earth are exposed to risks from seismic hazards. For more information, see WBDG Designing Buildings to Resist Explosive Threats section on Seismic vs. For example, were the Oklahoma Federal Building designed to seismic design standards, the damage caused by the blast would have been much less (refer to MAT Report FEMA 277). In addition, as a general rule, buildings designed to resist earthquakes should also resist blast (terrorism) or wind, suffering less damage. Third, and as important as the others, because earthquake forces are dynamic and each building responds according to its own design complexity, it is essential that the design team work collaboratively and have a common understanding of the terms and methods used in the seismic design process. Second, performance-based requirements, which may exceed the minimum life safety requirements of current seismic codes, must be established to respond appropriately to the threats and risks posed by natural hazards on the building's mission and occupants. First, the design team must take a multi-hazard approach towards design that accounts for the potential impacts of seismic forces as well as all the major hazards to which an area is vulnerable. The essence of successful seismic design is three-fold. This resource page provides an introduction to the concepts and principles of seismic design, including strategies for designing earthquake-resistant buildings to ensure the health, safety, and security of building occupants and assets.
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