Buildings at Risk - Seismic Flashcards
Accelerogram
The record from an accelerograph showing acceleration as a function of time.
Accelerograph
A strong motion earthquake instrument recording accelerations
Acceleration
rate of change of velocity with time
Aftershock
an earthquake, usually a member of an aftershock series often within the span of several months following the occurrence of a large earthquake (main shock). The magnitude of an aftershock is usually smaller than the main shock
Amplification
a relative increase in ground motion between one type of soil and another, or an increase in building response as result of resonance
Base Isolation
A method whereby a building superstructure is detected from its foundation in order to change the characteristics of earthquake forces transmitted to the building
Base Shear
Calculated total shear force acting at the base of a structure, used in codes as static representation of later earthquake forces. Also referred to as “equivalent lateral force”
Brittle Failure
Failure in a material which generally has a very limited plastic range; material subject to sudden failure without warning.
Damping
A rate at which natural vibration decays as a result of absorption of energy
Deflection
the state of being turned aside from a straight line, generally used in the horizontal sense
Amplitude
Maximum deviation from mean of the center line of a wave.
Diaphragm
a horizontal or nearly horizontal structural element designed to transmit lateral forces to the vertical elements of the seismic resisting system
Drift
Vertical deflection of a building or structure caused by lateral forces
Ductility
Property of some materials, such as steel, to distort when subjected to forces while still retaining considerable strength
Dynamic
Having to do with bodies in motion
Elastic
The ability of a material to return to its original form and condition after displacing force is removed.
Energy Absorption
Energy is absorbed as a structure distorts elastically.
Energy Dissipation
Reduction in intensity of earthquake shock waves with time and distance, or by transmission through discontinuous materials with different absorption capabilities
Epicenter
A point on the earths surface which is directly above the focus of an earthquake
Exceedance Probability
the probability that a specified level of ground motion or specified social or economic consequences of earthquakes will be exceeded at a site or in a region during a specified exposure time.
Exposure
The potential economic loss to all or certain subsets of the built environment as a result of one or more earthquakes in an area. This term usually refers to the insured value of structures carried by one or more insurers
Failure Mode
The manner in which a structure fails (column buckling, overturning, etc. )
Design Earthquake
In the NEHRP Provisions the earthquake that produces ground motions at the site under consideration that have a 90% probability of not being exceeded in 50 years (or a 10% probability of being exceeded). This is equivalent to a mean Return Period of 475 years, or an annual risk or 0.002 events a year.
Fault
A fracture in the earth’s crust accompanied by displacement of one side of the fracture with respect to the other and in a direction parallel to the fracture
Normal Fault
A fault under tension where the overlaying block moves down the dip or slop of the fault plane
Strike-Slip Fault
Or lateral slip, A fault whose relative displacement is purely horizontal
Thrust (Reverse) Fault
A fault under compression where the overlaying block moves up the dip of the fault plane
Oblique-Slip Fault
A combination of normal and slip or thrust and slip faults whose movement is diagonal along the dip of the fault plane
Describe the 6 Seismic design Categories
Category A: corresponds to building in areas where expected ground shaking is minor
Category B: corresponds to buildings of occupancy categories I, II, III in areas where moderately destructive ground shaking is expected
Category C: corresponds to buildings of the occupancy category IV, in areas where moderately destruction ground shaking might take place , and to I, II, III in areas where severe destructive ground shaking is expected
Category D: corresponds to buildings and structures in areas expected to experience severe and destructive ground shaking but not located close to major active fault lines.
Category E: corresponds to buildings of occupancy categories I, II, III in areas located near major active fault lines
Category F: corresponds to buildings of occupancy category IV in areas located near major active fault lines
Focus
The location of the fault break where an earthquake originates
Force
Agency or influence that tries to deform an object or overcome its resistance to motion
Braced Frame
One which is dependent upon diagonal braces for stability and capacity to resist lateral forces. In concentric braced frames, diagonal braces are arranged concentric to columns/beam joints; in eccentric braced frames, they are eccentric.