Structural Terms 1

Surface forces

Caused by direct contact of one body with the surface of another.

Body force

Developed when one body exerts a force on another without direct physical contact.

Prismatic

Cross sections are the same throughout its length.

Homogeneous material

Has the same properties throughout its volume.

Isotropic material

Has the same properties in all directions.

Load Factors

Reflect the probability of total loading occurrence.

Yielding

Occurs when stress exceeds the elastic limit, causing permanent deformation.

Yield stress

Stress causing yielding and plastic deformation.

Strain Hardening

Material can support increased load after yielding.

Ductile Materials

Can undergo large strains before fracturing.

Brittle Materials

Exhibit little or no yielding before failure.

Strain energy

Work stored in a material due to external load.

Modulus of Resilience

Strain-energy density at the proportional limit.

Modulus of Toughness

Represents the area under the stress-strain diagram.

Ductility Factor

Ratio of toughness to resilience modulus.

Creep

Continuous deformation under sustained load.

Fatigue

Breakdown due to repeated stress or strain cycles.

Plasticity

Material deforms permanently above elastic limit.

Residual Stress

Stress remaining after plastic deformation.

Beams

Slender members supporting perpendicular loads.

Dilatation

Change in volume per unit volume.

Resonance

Building period coincides with earthquake period.

Torsional Shear Stress

Occurs when mass center differs from rigidity center.

Ground Displacement

Measured by a seismometer.

Rigidity of a Structure

Reciprocal of deflection.

Story

Space between two adjacent floors.

Diaphragms

Transfer lateral forces to vertical elements.

Shear wall

Resists lateral forces on its plane.

Center of Gravity

Point with no torque from gravitational force.

Center of Rigidity

Point where lateral force resistance acts.

Center of Mass

Point where seismic force acts.

Eccentricity

Distance between rigidity and mass centers.

Design seismic base shear

Total lateral force.

Flexibility of a structure

Inverse of stiffness.

Story drift

Displacement between levels.

Story displacement

Lateral displacement of a story.

Damping

Rate of absorbing natural vibration.

Seismometer

Measures peak ground acceleration.

Magnetometer

Measures rock strain under pressure.

Focus (Hypocenter)

Origin of earthquake waves.

Epicenter

Point above the earthquake focus.

Story drift ratio

Drift divided by story height.

Intensity

Measure of earthquake shaking strength.

Magnitude

Measure of energy released in an earthquake.

Liquefaction

Soil loses shear strength during shaking.

Earthquake

Violent ground movement due to energy release.

Shear Drift

Building sideways deflection from lateral loads.

Chord Drift

Vertical load sideways deflection.

Resultant

Force determining equilibrium or motion.

Hooke’s Law

Principle for axially loaded material deformation.