Strength of Materials: Key Terms

Strength of Materials Terms

• Strain energy is the energy stored in a material due to deformation.
• Modulus of toughness indicates the maximum amount of strain-energy a material can absorb just before it fractures, which is the ability to absorb energy in the plastic range.
• Modulus of Resilience represents the largest amount of internal strain energy per unit volume that a material can absorb without causing permanent damage, which is the ability to absorb energy in the elastic range.
• Elasticity is the property of a material that allows it to return to its original state once the load is removed.
• Ductility is the ability of a material to deform in the plastic range without breaking.
• Stiffness is the ability to resist deformation within the linear range, equaling the force required to produce unit deformation; its inverse is flexibility.
• Toughness is a material's resistance to fracture.
• Hardness is a material's resistance to indentation.
• Ductile Material can be subjected to large strains before it fractures.
• Brittle Materials exhibit little or no yielding before failure.
• Homogeneous material has the same physical and mechanical properties throughout its volume, and has the same composition at any point.
• Isotropic material has the same physical and mechanical properties in all directions.
• Orthotropic material: Material which has properties that differ along three mutually-orthogonal axes at a particular point.
• Prismatic members possess the same cross sections throughout their length.
• Creep occurs when a material supporting a load for a long period continues to deform until sudden fracture or impaired usefulness; this time-dependent permanent deformation is known as creep.
• Fatigue occurs when a material subjected to repeated cycles of stress/strain causes its structure to break down, ultimately leading to fracture
• Buckling: Lateral deflection occurring when long slender members are subjected to an axial compressive force
• Yielding: A slight stress increase above the elastic limit results in material breakdown and permanent deformation, known as plastic deformation.
• Strain Hardening: Load increases until it reaches maximum stress, after yielding has ended.
• Necking: The cross-sectional area begins to decrease in a localized region of the specimen, just after the ultimate stress, until the specimen breaks at the fracture stress.

Earthquake Engineering Terms

• 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 in its own plane, typically wind and seismic loads.
  • Stiffened walls can transfer lateral forces from floors and roofs to the foundation.
• Center of gravity is the point where an object experiences no torque from gravitational force.
• Center of rigidity: The center of resistance of a floor/diaphragm against lateral forces.
  • Its is where resistance to the applied lateral force acts.
• Center of mass: the point through which the resultant of the masses of a system acts
  • It is the point through which the applied lateral force acts.
• Center of stiffness: This is where the restoring forces of a system acts.
• Eccentricity is the distance between the center of rigidity and the center of mass.
• Design seismic base shear is the total design lateral force at the base of a structure.
• Story drift: The lateral displacement of one level relative to the level above or below.
• Story displacement: The lateral displacement of the story relative to the base
• Out-of-plane offsets: The discontinuities in a lateral force path
• Torsional shear stress: The shear stress when the structure's center of mass does not coincide with its center of rigidity
• Resonance: The phenomenon occurring when a building period coincides with the earthquake period.
• Natural period: The time period of undamped free vibration of a structure.
• Damping: The rate at which natural vibration is absorbed.
  • Internal friction, imperfect elasticity of material, slipping, sliding, reduce the amplitude of vibration
• Epicenter: The geographical surface point vertically above the earthquake focus.
• Focus: The origin/source of elastic waves inside the earth causes ground shaking.
• Ductility: The capacity to undergo large inelastic deformations without significant loss of strength or stiffness.
• Liquefaction is the state in saturated cohesionless soil where effective shear strength is reduced to negligible value; soil tends to behave like a fluid mass.
• Intensity measures the shaking strength during an earthquake
• Magnitude measures the energy released in an earthquake.
• Seismograph: Instrument used to record ground motion during an earthquake.
• Soft Storey Irregularity: Lateral stiffness is less than 70% of the storey above, or less than 80% of the average lateral stiffness of the three storeys above.
• Weak Storey Irregularity: Storey lateral strength is less than 80% of that in the storey above.