PSAD Terms

Practice vocabulary flashcards covering structural engineering, mechanics of deformable bodies, stress-strain behavior, seismic parameters, and building irregularities.

Stress-Strain Diagram

A diagram plotting tensile stress ($\sigma$) versus strain ($\epsilon$), illustrating regions of elastic behavior, yielding, strain hardening, necking, and fracture.

Surface Forces

Forces caused by the direct contact of one body with the surface of another.

Body Force

A force developed when one body exerts a force on another body without direct physical contact between the bodies.

Prismatic

All cross sections of a member are the same throughout its length.

Homogeneous Material

Has the same physical and mechanical properties or composition throughout its volume.

Isotropic Material

Has the same properties in all directions

Load Factors

Factors that reflect the probability that the total loading $R$ will occur for all the stated events.

Resistance Factors ($\phi$)

Factors determined from the probability of material failure as it relates to the material's qualilty and the consistency of its strength.

Shear Strain

The change in angle that occurs between two line segments that are originally perpendicular to one another.

Yielding

A slight increase in stress above the elastic limit will result in a breakdown of the material and cause it to deform permanently.

Yield Stress ($\sigma_Y$)

The stress that causes yielding, marked by an increase in strain without an increase in stress.

Plastic Deformation

The permanent elongation or deformation that remains in a material after yielding occurs.

Strain Hardening

When yielding has ended, an increase in load can be supported, producing a continuously rising curve that flattens until reaching the ultimate stress.

Necking

Up to the ultimate stress, as the specimen elongates, it's cross-sectional area will decrease.

Ductile Materials

Materials that can be subjected to large strains before it fractures.

Brittle Materials

Materials that exhibit little or no yielding before failure.

Strain Energy

Internal energy stored in a material as external work is performed on it by an external load during deformation.

Modulus of Resilience

Ability to absorb energy in elastic range.

Modulus of Toughness

Ability to absorb energy in plastic range.

Ductility Factor

The ratio of the modulus of toughness to the modulus of resilience.

Creep

When a material has to support a load for a very long period of time, it may continue to deform until a sudden fracture occurs or its usefulness is impaired.

Fatigue

When a metal is subjected to repeated cycles of stress or strain, it causes its structure to break down, ultimately leading to fracture.

Plasticity

A material breakdown and deforms permanently even due to a slight increase in stress above the elastic limit.

Residual Stress

The internal stress that develops in a beam when the plastic moment is removed.

Beams

Slender members that support loadings applied perpendicular to their longitudinal axis.

Dilatation

The change in volume per unit volume, also referred to as volumetric strain.

Resonance

When a building period coincides with the earthquake period.

Torsional Shear Stress

When the center of mass of a structure does not coincide with its center of rigidity.

Rigidity of a Structure

The reciprocal of deflection.

Story

The space between two adjacent floors.

Diaphragms

Rigid horizontal planes used to transfer lateral forces to vertical resisting elements.

Shear Wall

A wall designed to resist lateral forces acting on its own plane, typically from wind and seismic loads.

Center of Gravity

The point where an object suffers no torque from the gravitational force acting upon it.

Center of Rigidity

The point through which the resultant of the resistance to the applied lateral force acts.

Center of Mass

The point through which the applied seismic force acts.

Eccentricity

The distance between the center of rigidity and the center of mass.

Design Seismic Base Shear

The total design lateral force acting at the base of a structure.

Flexibility of a Structure

Inverse of stiffness

Story Drift

Displacement of one level relative to the level above or below it.

Story Displacement

The lateral displacement of a story relative to the base.

Damping

Rate at which the natural vibration of a structure is absorbed.

Seismometer

Instrument used to measure the peak ground acceleration.

Magnetometer

Instrument used to measure the strain of rock under pressure.

Focus (Hypocenter)

The originating source of elastic waves inside the earth that cause shaking during an earthquake.

Epicenter

The point on the Earth's surface directly above the focus.

Story Drift Ratio

story drift divided by the story height

Intensity

Measure of the strength of shaking during earthquake.

Magnitude

Measure of the energy released in an earthquake.

Liquefaction

State in saturated cohesionless soil wherein the effective shear strength is reduced to negligible value.

Earthquake

An oscillatory, sometimes violent movement of the ground's surface following a release of energy in the Earth's crust.

Shear Drift

The sideways deflection of a building caused by lateral (sideways) loads.

Chord Drift

The sideways deflection of axial (vertical) loads.

Stiffness Irregularity - Soft Storey

The lateral stiffness is less than $70\,\%$ of that in the storey above, or less than $80\,\%$ of the average stiffness of the three storeys above.

Weight (Mass) Irregularity

The effective mass of any storey is more than $150\,\%$ of the effective mass of an adjacent storey (excluding lighter roofs).

Vertical Geometric Irregularity

The horizontal dimension of the lateral-force-resisting system in any storey exceeds $130\,\%$ of that in an adjacent storey (excluding one-storey penthouses).

In-Plane Discontinuity In Vertical Lateral-force-Resisting Element Irregularity

An in-plane offset of the lateral-load-resisting elements that is greater than the length of those elements.

Discontinuity In Capacity - Weak Storey Irregularity

The storey strength is less than $80\,\%$ of that in the storey above.

Torsional Irregularity

The maximum storey drift (including accidental torsion) at one end transverse to an axis is more than $1.2$ times the average of the storey drifts of the two ends.

Re-Entrant Corner Irregularity

A plan irregularity where both projections of a structure beyond a re-entrant corner exceed $15\,\%$ of the plan dimension in that direction.

Diaphragm Discontinuity Irregularity

When diaphragms have cutout or open areas greater than $50\,\%$ of the gross enclosed area, or changes in effective stiffness of more than $50\,\%$ from one story to the next.

Out of Plane Offsets Irregularity

Consisting of discontinuities in a lateral force path, such as out-of-plane offsets of the vertical elements.

Non-Parallel Systems Irregularity

Where vertical lateral-load-resisting elements are not parallel to or symmetric about the major orthogonal axes of the lateral force-resisting system.

Hooke's Law

The principle stating that stress is proportional to strain within the elastic region.

Resultant

Force which determines whether the body will be in equilibrium or will have a varying state of motion.

Poisson's Ratio

Ratio of lateral to longitudinal strain is constant.

Young's Modulus

The constant of proportionality defining the linear relationship between stress and strain.

Column

A structural member having a ratio of unsupported height to least lateral dimension not less than $3$, used primarily to support axial load.

Kinetic Friction

Retarding force acting opposite of a body in motion.

Proportional Limit

Value beyond which stress is no longer proportional to the strain.

Elastic Limit

Greatest stress a material is capable of developing without a permanent elongation remaining upon complete unloading of the specimen.

Pre-Tensioning

The process of stressing high-strength steel wires before concrete hardens.

Post-Tensioning

The process of stressing high-strength steel after concrete has been cast and has attained sufficient strength.

Relaxation

The loss of stress that take place with the passage of time as concrete is held at a constant strain.

Elasticity

The property of a material enabling it to return to its original dimensions when an applied load is removed.

Orthotropic Material

Same composition at every point but the elastic may not be the same in all directions.

Focal Depth

The vertical distance describing earthquake location beneath the epicenter.

Ultimate Stress

Maximum stress a material is capable of developing

Rupture Strength

The stress at which a specimen actually breaks.

Stiffness

The property of a material to withstand high stress without large strain.

Brittleness

Absence of any plastic deformation prior to failure.

Malleability

Property of a material enabling it to undergo considerable plastic deformation under compressive load before actual rupture.

Factor of Safety

The ratio of the failure stress to the allowable stress.

Failure

The condition that renders a load-resisting member unfit for resisting further increases in load.

Diagonal Tension

Tensile stress that develops across a diagonal surface.

Tangent Modulus

Rate of change of stress with respect to strain.

Specific Strength

The ratio of ultimate or tensile strength to the specific weight (weight per unit volume).

Specific Modulus

The ratio of Young's modulus to the specific weight.

Seismograph

A ground-mounted device that measures the actual displacement of the ground relative to a stationary reference point.

Dynamic Forces

Forces generated by the motion of a body.