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.
Moment Frame
A space frame in which members and joints are capable of resisting lateral forces by bending as well as along the axis of the members. varying levels of resistance are provided by Ordinary, Intermediate, and Special Moment frames as defined in the NEHRP provisions with special frames providing the most resistance.
Frame, Space
A structural system composed of interconnected members, other than bearing walls, that is capable of supporting vertical loads and that may also provide resistance to seismic forces.
Frequency
Referring to vibrations, the number of wave peaks which pass through a point in a unit of time, usually measured in cycles per second.
Ground Failure
Physical changes to the ground surface produced by an earthquake, such as lateral spreading, landslides, and liquefaction.
“G”
The acceleration due to gravity, or 32’ per second
Inelastic
The inability of a material to return to its original form and condition after a displacing force is removed, permanent distortion
Intensity
A subjective measure of the force of an earthquake at a particular place as measured by its effects on person, structures, and earth materials. Intensity is a measure of energy. The principle scaled used in the United States today is the Modified Mercalli, 1956 version.
Irregular
Deviation of a building configuration from a simple symmetrical shape.
Lateral Force Coefficients
Factors applied to the weight of a structure or its parts to determine lateral forces for seismic design
Liquefaction
Transformation of a granular material (soil) from a solid state into a liquefied state as a consequence of increased pore-water pressure induced by vibration
Microzone (microzonation)
seismic zoing, generally by use of maps, for land areas smaller than regions shown in typical seismic code maps, but larger than individual building sites
Irregular
Deviation of a building configuration from a simple symmetrical shape.
Nonstructural Components
Those building components which are not intended primarily for structural support and bracing of the building
Liquefaction
Transformation of a granular material (soil) from a solid state into a liquefied state as a consequence of increased pore-water pressure induced by vibration
Microzone (microzonation)
seismic zoing, generally by use of maps, for land areas smaller than regions shown in typical seismic code maps, but larger than individual building sites
Modal Analysis
determination of seismic design forces based upon the theoretical response of a structure to excitation in its several modes of vibration
Nonstructural Components
Those building components which are not intended primarily for structural support and bracing of the building
Out of Phase
The state where a structure in motion is not at the same frequency as the ground motion or an adjoining structure, or where equipment in a building vibrates at a different frequency from the structure.
Period
The elapsed time (generally in seconds) of a single cycle of a vibratory motion or oscillation: the inverse of frequency
Resonance
The amplification of a vibratory motion occurring when the period of an impulse or periodic stimulus coincides with the period of the oscillating body.
Seismic zone
Generally, areas defined on the map within which seismic design requirements are constant. In the NEHRP provisions, seismic zones are defined by both contour line and county boundaries
Shear
A force which acts by attempting to cause the fibers or planes of an object to slide over one another
Soil structure interaction
The effects of the properties of both soil and structure upon response of the structure
Spectrum
A plot for a specific site indicating maximum earthquake response with respect to natural period or frequency of the structure or element. The response can be measured as acceleration, velocity, displacement or other properties.
Speed
Rate of change of distance traveled with time, irrespective of directions
Stiffness
Resistance to deflection or Drift of a structural component or system
Story drift
Vertical deflection of a single story of a building caused by lateral forces.
Strain
Deformation of a material per unit of the original dimension
Strength
The capability of a material or structural member to resist or withstand applied forces
Stress
Applied load per unit area, or internal resistance within a material that opposes a forces attempt to deform.
System
An assembly of components or elements designed to perform a specific function, such as structural system
Torque
The action of forced the tends to produce torsion. The product of a force and lever arm, as in the action of using a wrench to tighten a nut.
Tsunami
A sea wave produced by large area displacement of the ocean bottom, the result of earthquakes or volcanic eruptions
Velocity
Rate of change of distance traveled with time in a given direction. In earthquakes, it usually refers to seismic waves and is expressed and inches or centimeters per second.
Rigidity
Relative stiffness of a structure or element. And numerical terms, equal to the reciprocal of displacement caused by unit force.
Seismic
Of, subject to, or caused by an earthquake or in earth vibration.
Seismic event
That abrupt release of energy in the earths lithosphere causing an earth vibration: an earthquake.
Seismic hazard
Any physical phenomenon such as ground shaking or ground failure associated with an earthquake that may produce adverse effects on the built environment and human activities: also, the probability of earthquakes of defined magnitude or intensity affecting a given location.
Seismic performance category
A classification assigned and the NEHRP provisions to the building based on it’s seismic hazard exposure group and it’s seismic hazard.
Seismic resisting system
The part of the structural system that is designed to provide required resistance to prescribed seismic forces
Seismic risk
The probability that social or economic consequences of an earthquake will equal or exceed specified values at a site during a specified exposure time: in general, seismic risk is vulnerability multiplied by the seismic hazard.
Richter magnitude ( or scale )
A measure of earthquake size which is determined by taking the common logarithm (base 10) of the largest ground motion recorded during the arrival of a P-wave or seismic surface wave and applying a standard correction for distance to the epicenter. The scale is named after its creator, American size otologist Charles R Richter.
Return period
The time period In years in which the probability is 63% that an earthquake of a certain magnitude will recur.
Wall, bearing
A wall providing support for vertical loads: it may be interior or exterior
Wall, sheer
A wall, bearing or non-bearing, designed to resist seismic forces acting in the plane of the wall
P – wave
The primary, or fastest waves traveling away from a fault rupture through the Earth’s crust, and consisting of a series of compressions and dilations of the ground material.
Rayleigh wave
Forward and vertical vibration of seismic surface waves.
S – wave
Shear, or secondary wave, produced essentially by the shearing or tearing motions of earthquakes at right angles to the direction of wave propagation.
