NEC Civil Engineering key terms

The permanent, stationary weight a structure must carry, including its own framing, floors, walls, roofing, fixed equipment, and any attached finishes that stay in place for the life of the building.

A variable gravity load produced by occupancy and use, such as people, furniture, stored goods, and movable equipment; design values are tabulated by occupancy type and reduced for large tributary areas.

A factored arrangement of simultaneous loads used to check a structure for a required strength level, applying different multipliers to dead, live, wind, seismic, and other effects depending on the governing design case.

A limit-states design method that multiplies nominal loads by factors greater than one and nominal resistances by factors less than one, so that the factored resistance equals or exceeds the factored load effect.

A design method in which computed service-level stresses are kept below a permissible fraction of the material's yield or ultimate strength, using a single factor of safety rather than separate load and resistance factors.

A structural element, typically a beam or slab, that resists transverse loads primarily by internal bending, developing compression on one side of the neutral axis and tension on the other.

The line across a bending cross-section where longitudinal strain is zero, separating the compressed zone from the stretched zone; for a homogeneous elastic section it passes through the centroid.

A geometric property of a cross-section, equal to the sum of elemental areas times the square of their distance from an axis, that measures resistance to bending about that axis.

The moment of inertia of a cross-section divided by its distance to the extreme fiber, giving a single value that converts bending moment directly into maximum bending stress.

The internal transverse force at a section of a member, equal to the algebraic sum of all external forces acting to one side of that section; it governs web and connector design in beams.

A plot of internal bending moment along a member's length, whose slope equals the shear force at each point; it identifies maximum positive and negative moments used for sizing sections and reinforcement.

The point along a member where the bending moment passes through zero and changes sign, so curvature reverses; it is often a location for reduced reinforcement or splice points.

Sudden loss of stability in a slender compression member or plate when the applied load reaches a critical value, causing large lateral deformation rather than simple material crushing.

The effective length of a compression member divided by its least radius of gyration; a higher value means greater susceptibility to buckling and lower allowable compressive stress.

The equivalent pin-ended length of a column that accounts for end restraint conditions, used in buckling calculations so that fixed, pinned, or free ends are treated consistently.

A composite material in which steel bars carry tensile forces that concrete cannot, while the concrete resists compression and protects the steel; the two materials act together through bond and similar thermal movement.

The distance from the extreme compression fiber of a concrete section to the centroid of the tension reinforcement, used to compute the internal lever arm and flexural capacity.

A reinforced concrete cross-section proportioned so that concrete crushing and steel yielding occur simultaneously at ultimate strength, marking the boundary between tension-controlled and compression-controlled behavior.

The embedded length of a reinforcing bar required to transfer its design force into the surrounding concrete by bond without pulling out, influenced by bar size, cover, spacing, and concrete strength.

A connection in which two reinforcing bars overlap for a specified length so that force transfers from one bar to the other through the surrounding concrete; the required overlap relates to development length.

Concrete in which internal compressive stress is deliberately introduced before service loads, typically by tensioned high-strength tendons, to offset tensile stresses from bending and control cracking.

A prestressing technique in which steel tendons are tensioned after the concrete has hardened and then anchored against the member ends, often inside ducts that are later grouted.

A vertical wall designed to resist in-plane lateral forces such as wind or earthquake, transferring them down to the foundation and adding significant stiffness to the building frame.

A horizontal or sloped structural system, such as a floor slab or roof deck, that collects lateral forces and distributes them to vertical resisting elements like shear walls or braced frames.

A horizontal force acting on a structure, usually from wind pressure or earthquake ground motion, which must be carried by frames, walls, or bracing down to the foundation.

The total lateral force assumed at the base of a structure in a seismic analysis, derived from the building's effective seismic weight and a response coefficient, then distributed over the height.

A classification assigned to a structure based on its occupancy risk and the site's seismic hazard, which determines the permitted structural systems and detailing requirements.

The ability of a material or structural system to undergo large inelastic deformation without losing strength, allowing energy dissipation during earthquakes and warning before collapse.

The maximum pressure a soil or rock mass can support beneath a foundation without shear failure or excessive settlement; it is compared with applied footing pressure using a factor of safety.

The downward movement of a foundation caused by compression or consolidation of the supporting soil under load; differential settlement between parts of a structure is especially damaging.

The time-dependent volume decrease of saturated fine-grained soil as water is squeezed out of its voids under sustained load, producing gradual settlement over months or years.

The volume of voids in a soil mass divided by the volume of solid particles; it indicates how loose or dense a soil is and governs compressibility, permeability, and shear strength.

The resistance of a soil mass to sliding along internal planes, described by cohesion and angle of internal friction; it controls bearing capacity, slope stability, and lateral earth pressure.

A foundation such as a spread footing or mat that transfers load to soil relatively near the ground surface, typically at a depth small compared with its width.

A foundation element such as a driven pile or drilled shaft that carries load to competent strata far below the surface, mobilizing capacity through end bearing and side friction.

The minimum horizontal pressure exerted by retained soil when a wall yields slightly away from the backfill, allowing the soil mass to expand and mobilize its shear resistance.

A structure built to hold back soil or other material where a slope change is needed, designed to resist lateral earth pressure, surcharge, water pressure, and overturning or sliding.

The change in hydraulic head per unit distance along a flow path through soil; it drives seepage and, if large enough, can cause piping or boiling at an exit surface.

A soil's capacity to transmit water through its connected voids, expressed as a coefficient of hydraulic conductivity; it governs seepage rate, drainage design, and consolidation time.

Internal erosion in which seepage carries fine soil particles out of a mass, progressively forming a channel that can lead to structural failure of a dam, levee, or excavation.