ESE CE Prelims key terms

The ratio of a structure's or material's capacity to resist load to the load or stress actually expected to act on it. Values above one indicate reserve strength against uncertainty, variation, and failure.

A design philosophy that verifies a structure will not become unfit for use, checking both ultimate states such as collapse and serviceability states such as excessive deflection or cracking, using partial factors applied to loads and resistances.

A traditional design method in which computed working stresses from service loads must not exceed a permissible stress obtained by dividing a material's strength by a factor of safety.

A condition in which a structure remains safe but fails a performance requirement such as deflection, vibration, crack width, or durability, making it unfit for its intended normal use.

A multiplier applied to nominal or characteristic loads to account for possible overload, uncertainty in load estimation, and the lower probability of several loads acting simultaneously at full value.

The permanent, self-weight loading on a structure, comprising the weight of structural members plus fixed non-structural elements such as floors, finishes, partitions, and permanently attached services.

A variable gravity load produced by occupancy and use, including people, furniture, stored goods, and movable equipment. Its magnitude is specified by code and depends on the occupancy category.

The internal moment at a section of a beam equal to the algebraic sum of moments of all external forces acting on one side of that section about the section's centroidal axis.

The internal transverse force at a section of a member, equal to the algebraic sum of all external forces acting perpendicular to the member axis on one side of the section.

A geometric property of a cross-section equal to the second moment of area divided by the distance from the neutral axis to the extreme fibre, used to compute maximum bending stress from moment.

The second moment of area of a cross-section about a specified axis, measuring how the area is distributed relative to that axis and governing resistance to bending and deflection.

The square root of the second moment of area divided by the cross-sectional area. It represents the distance at which the whole area could be concentrated to give the same moment of inertia.

A sudden loss of stability of a slender compression member or plate, occurring at a critical load that depends on stiffness, length, and end restraint rather than on material strength alone.

The equivalent pin-ended length of a compression member that produces the same buckling load as the actual member with its real end restraints and bracing conditions.

The ratio of a compression member's effective length to its least radius of gyration, indicating how susceptible the member is to buckling rather than to direct crushing failure.

The intensity of internal force acting parallel to a surface within a material, commonly computed as shear force divided by area for average values in bolts, welds, and beam webs.

The contact pressure between two bodies transmitting force over a limited area, such as a bolt pressing against a plate hole or a beam resting on a support, calculated as load divided by projected contact area.

A plot of applied stress against resulting strain for a material under load, revealing its elastic modulus, yield point, ultimate strength, ductility, and toughness characteristics.

The stress at which a material begins to deform plastically, producing permanent strain that remains after load removal. It is commonly defined using a 0.2 percent offset for materials without a distinct yield plateau.

The slope of the linear elastic portion of a stress-strain curve, expressing the stiffness of a material as the ratio of normal stress to corresponding axial strain.

The negative ratio of lateral strain to axial strain in a material subjected to uniaxial stress, typically near 0.3 for steel and 0.15 to 0.2 for concrete.

The ability of a material to undergo significant plastic deformation before fracture, allowing warning of failure and redistribution of stress in statically indeterminate structures.

The maximum stress a material can sustain before rupture or before significant load drop, obtained as peak load divided by original cross-sectional area in a tension test.

The displacement of a point on a structural member from its unloaded position, governed by span, load magnitude, and flexural stiffness, and limited by serviceability criteria.

A graph showing the variation of internal bending moment along a member's length, used to locate maximum moment and points of contraflexure for design and detailing.

A graph showing how internal transverse force varies along a member. Its slope equals the applied distributed load, and it crosses zero where bending moment reaches a maximum or minimum.

A structure with more unknown reactions or internal forces than available equilibrium equations, so its force distribution depends on the relative stiffness of its members.

The maximum pressure the soil beneath a foundation can support without shear failure or excessive settlement, determined from soil shear strength parameters and foundation geometry and depth.

The downward movement of a foundation or embankment caused by compression of underlying soil under applied load, often the controlling criterion for foundation design on soft ground.

The time-dependent reduction in volume of a saturated soil due to expulsion of pore water under sustained loading, producing settlement that continues long after load application.

The intergranular stress carried by the soil skeleton, equal to total stress minus pore water pressure. It controls shear strength, compression, and volume change in saturated soils.

An in-situ soil test in which a split-spoon sampler is driven by a standard hammer, with the blow count for the final 300 mm recorded as an index of soil density and strength.

Loss of soil shear strength when saturated loose sandy soil is shaken and pore water pressure rises to equal total stress, so the soil behaves temporarily like a fluid.

The change in hydraulic head per unit length of flow path through a porous medium. It drives seepage and, when excessive, can cause piping or boiling in granular soils.

A relationship stating that the discharge velocity through a porous medium equals the product of hydraulic conductivity and hydraulic gradient, valid for laminar flow in soils.

The property of a soil or rock describing how readily water flows through its interconnected voids, expressed as hydraulic conductivity and influenced strongly by particle size and void ratio.

The mass ratio of water to cementitious material in a concrete mix. Lower values increase strength and durability but reduce workability, making it the key parameter in mix design.

The ease with which fresh concrete can be mixed, transported, placed, and compacted without segregation, commonly assessed in the field by the slump test.

A simple field test measuring the vertical drop of a freshly moulded concrete cone when the mould is removed, indicating consistency and workability of the mix.

The process of maintaining adequate moisture and temperature in concrete after placement so that cement hydration continues and the designed strength and durability develop.

The maximum stress a hardened concrete specimen can carry in compression, usually determined from standard cube or cylinder tests at a specified age and used as the primary grade indicator.

A composite material in which steel bars carry tensile forces that concrete cannot resist, while concrete protects the steel and resists compression, with bond ensuring the two act together.

The minimum embedded length of reinforcement required to transfer the bar's force to the surrounding concrete through bond without the bar pulling out.

A connection in which two reinforcing bars overlap so that force transfers from one to the other through bond over the lap length, typically specified as a multiple of development length.

Concrete in which internal compressive stress is deliberately introduced, usually by tensioned high-strength steel, to offset tensile stresses from loads and control cracking.

A load applied suddenly or with kinetic energy, producing dynamic stresses and deflections larger than those from an equal static load because of inertia and energy absorption effects.