BEM PCE Civil & Structural key terms

The representative value of a load, such as dead, live, wind, or imposed load, that is not expected to be exceeded with a stated probability during the design life. Design values are derived by applying partial factors to it.

A multiplier applied to a characteristic load or material strength to account for uncertainty, variability, and the consequences of failure. Load factors are typically greater than one and resistance factors less than one.

A design philosophy that verifies a structure will not become unfit for use under defined conditions. Ultimate limit states cover safety against collapse, while serviceability limit states cover deflection, vibration, and cracking.

A condition where the structure or a member reaches its maximum load-carrying capacity, such as flexural failure, shear failure, buckling, or overturning. Design must prevent it with adequate reliability.

A condition where the structure remains safe but becomes unfit for normal use, for example excessive deflection, cracking, or vibration. These limits are checked under characteristic or frequent load combinations.

A defined arrangement of simultaneous loads, each multiplied by a factor, used to check a limit state. Combinations account for the likelihood of loads acting together, such as dead plus live plus wind.

The permanent self-weight of the structure and any fixed non-structural elements, such as finishes, partitions, and services. Its magnitude is calculated from material densities and geometry.

A variable imposed load caused by occupancy and use, such as people, furniture, and movable equipment. Values are specified by occupancy category and are treated as statistically variable.

A non-permanent load applied to a structure during normal use, including occupants, stored materials, and construction operations. The term is common in British and European codes for live load.

The permanent load from non-structural elements added to the structure, such as floor finishes, ceilings, and partitions. It is distinguished from the self-weight of the structural frame itself.

A horizontal pressure or suction on a structure caused by wind, varying with height, terrain roughness, and building shape. It is treated as a variable action with dynamic effects considered for tall or flexible structures.

The total horizontal design force at the base of a structure resulting from earthquake excitation. It is derived from the seismic weight, a design response spectrum, and the fundamental period.

The longest natural period of vibration of a structure, in seconds. It governs how the structure responds to earthquake ground motion and is estimated from height or analysis.

The ability of a component or structure to undergo large inelastic deformation without losing strength or collapsing. It is essential for energy dissipation during seismic events and for safe failure modes.

A zone where a structural member yields in bending and rotates plastically while maintaining a moment capacity. Controlled hinge locations are designed to provide ductility and warning before collapse.

The internal moment at a section of a member caused by forces acting at a distance from that section. It produces bending stresses varying linearly across the section and drives flexural design.

The internal force acting parallel to a section of a member, tending to slide one part relative to another. It produces shear stress and must be resisted by the concrete, stirrups, or steel section.

Steel, usually in the form of stirrups or links, placed to resist shear forces in a member. It also confines concrete, restrains longitudinal bars, and improves ductility.

The maximum bending moment a section can resist before failing. In reinforced concrete it is calculated from the steel area, steel yield strength, concrete strength, and effective depth.

A geometric property equal to the second moment of area divided by the distance from the neutral axis to the extreme fiber. It relates bending moment to maximum bending stress.

A geometric property describing how an area is distributed about an axis, determining resistance to bending. It is used to calculate deflection and bending stress in structural sections.

The displacement of a point on a structure from its original position under load. It is checked at serviceability limit states to prevent damage to finishes and discomfort to occupants.

A sudden loss of stability in a slender member under compressive load, causing lateral displacement and a reduction in load capacity. It is checked by considering effective length and slenderness.

The ratio of a member's effective length to its least radius of gyration, indicating its susceptibility to buckling. Higher values mean greater buckling risk and lower compressive capacity.

The theoretical length of a compression member used in buckling calculations, adjusted by a factor for end restraint. It reflects whether ends are pinned, fixed, or free.

Steel bars or mesh embedded in concrete to resist tensile and shear forces that concrete cannot carry. Its area, spacing, anchorage, and cover are specified in design codes.

The thickness of concrete between the outer surface of reinforcement and the nearest concrete face. It protects steel from corrosion and fire, and ensures bond and anchorage.

The ability of a structure or material to resist deterioration over its design life under exposure conditions. It depends on material quality, cover, crack control, and environmental protection.

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

The downward movement of a foundation or ground surface caused by load or soil volume change. Differential settlement between supports can cause structural distortion and cracking.

The ratio of available strength or resistance to the applied load or stress. A value greater than one indicates reserve capacity against failure; it is used in allowable stress and geotechnical design.

The lowest part of a structure that transfers loads to the ground. Shallow foundations spread load near the surface, while deep foundations use piles or caissons to reach stronger strata.

A slender deep foundation element installed in the ground to carry loads through weak soil to a stronger layer. Piles resist load by end bearing and shaft friction.

A structure that holds back soil or other material where a change in ground level occurs. It is designed for lateral earth pressure, surcharge, water pressure, and stability against sliding and overturning.

The horizontal pressure exerted by soil on a retaining structure. It depends on soil unit weight, friction angle, and wall movement, with active, passive, and at-rest conditions.

The mass of water divided by the mass of cement in a concrete mix. Lower ratios increase strength and durability but reduce workability, so admixtures may be needed.

The ease with which fresh concrete can be mixed, placed, compacted, and finished without segregation. It is commonly assessed by slump or flow tests and influenced by water content and admixtures.

The ability of hardened concrete to resist stress, usually expressed as characteristic compressive cube or cylinder strength at 28 days. It increases with lower water-cement ratio and proper curing.

The process of maintaining adequate moisture and temperature in concrete after placing so cement hydration can continue. Proper curing improves strength, durability, and reduces cracking.