SE Exam key terms

The weight of permanent construction and fixed equipment - structural framing, floors, roofs, walls, ceilings, finishes, and mechanical systems. It is computed from material densities and member volumes and remains essentially constant throughout the life of the building.

Gravity load produced by the intended occupancy and use of a space - people, furniture, movable equipment, and stored materials. Codes publish minimum design values by occupancy because the real loading varies unpredictably in magnitude and location.

The portion of a floor or roof surface whose load is delivered to one particular beam, column, or wall. Its boundaries run along the midlines between adjacent supports, and it converts an area load into a line or point load.

A diagram showing how one specific response - a reaction, shear, or moment at a chosen location - changes as a single unit load moves across the structure. It identifies the load positions that produce the extreme value.

The location along a bending member where the bending moment passes through zero and the curvature reverses sense. In continuous beams and frames it commonly falls near midspan or within a span next to a support.

Applying live load to only some spans of a continuous beam or frame so as to maximize a chosen effect, such as positive moment in one span or negative moment over a support.

The bending moment that develops at a fully restrained end of a loaded span when rotation there is prevented. It is the starting value for moment distribution and for judging continuity in indeterminate beams and frames.

A hand analysis technique for continuous beams and frames that repeatedly unlocks temporarily fixed joints, distributes the unbalanced moment in proportion to member stiffness, and carries part of it to far ends until the imbalance becomes negligible.

A device, most often a headed stud welded to a steel beam and embedded in the slab above, that ties steel and concrete together so they act as one composite member by transferring horizontal shear at the interface.

The reduced width of slab assumed to cooperate with a beam in composite design. It is narrower than the physical slab because shear lag prevents the outer portions from reaching the same stress as the region near the beam.

Shear stress concentrated around a column, load, or footing on a flat plate, which tends to drive a plug of concrete through the slab. It is resisted by slab thickness, drop panels, capitals, or added shear reinforcement.

A slab supported along all four edges with a long-to-short span ratio below roughly two, so load is carried in both directions. It may be analyzed by plate theory, tabulated coefficient methods, or yield-line theory.

Extra internal forces created because loads act on the already displaced shape of a structure. The resulting magnification of moments and shears is significant in slender columns and in frames that sway laterally.

A design criterion on behavior under normal service loads rather than on strength - deflection, vibration, or crack width. Satisfying it protects finishes, cladding, drainage, and occupant comfort over the life of the building.

An intentional upward curvature built into a beam, girder, or slab so that it looks level, or sags less noticeably, after dead load is applied. It is commonly specified for long-span steel and prestressed members.

The continuous route by which gravity or lateral force travels from where it is applied, through slabs, beams, columns, walls, connections, and foundations, into the ground. Every link must have strength and stiffness to pass the force along.

A region of a ductile member that has yielded in flexure and can rotate at nearly constant moment, redistributing internal forces. Where such hinges form, and how far they rotate, controls plastic collapse mechanisms.

A member that resists axial force and bending moment at the same time, so the two demands interact rather than simply adding. Design checks use interaction equations and amplified moments that reflect the member's deflected shape.

The total horizontal force at the base of a structure from earthquake or wind action, equal to the sum of the lateral forces applied over its height. It anchors the design of foundations and of the vertical lateral-force-resisting elements.

A code factor, R, that reduces the elastic seismic demand to a design level in recognition of a system's ductility, overstrength, and redundancy. Larger values apply to systems expected to deform well beyond yield without losing strength.

A factor, Cd, applied to elastically computed lateral displacements to estimate the largest inelastic displacement expected during the design earthquake. It is used when checking story drift and separation between adjacent structures.

The horizontal displacement of one floor relative to the floor immediately below it under lateral load. Codes cap it to limit damage to cladding, partitions, and glazing, and to control instability from gravity loads on the displaced frame.

A floor or roof system that collects lateral forces and delivers them to the vertical elements that resist them. Depending on its stiffness relative to those elements it may be modeled as rigid, as flexible, or as something in between.

A member within a diaphragm that drags lateral force from an area of the floor to a lateral-force-resisting element. It is especially important where the diaphragm is interrupted or where forces concentrate at a reentrant corner.

The edge or perimeter member of a diaphragm that resists the flexural tension and compression generated when the diaphragm bends as a deep horizontal beam spanning between lateral-force-resisting elements.

A vertical wall proportioned to resist in-plane lateral forces mainly through shear, and often also carrying gravity load. It may be built of reinforced concrete, masonry, or wood and can be detailed as ductile or as nearly elastic.

A frame whose beams and columns are joined by moment-resisting connections, obtaining lateral stiffness and strength from flexural action with no diagonal bracing. Ductile detailing lets it sway inelastically without losing stability.

A braced frame in which the diagonal brace lands on the beam away from the column, deliberately creating a short link segment that yields in shear or bending and dissipates seismic energy while the braces stay elastic.

A plan condition in which story drifts at one edge of a building are substantially larger than at the other, showing that mass or stiffness is unevenly arranged and that the structure twists noticeably under lateral load.

A code-prescribed offset between the applied lateral force and the center of mass, introduced to cover uncertain mass distribution and real-world asymmetry. It produces a design torsion even in buildings that appear perfectly symmetric.

The natural period of a structure's slowest mode of vibration, fixed by its mass and stiffness. Code expressions estimate it to read spectral acceleration from the design spectrum, and longer periods generally bring lower seismic demand.

A letter classification of the soil and rock beneath a site, based on shear wave velocity or penetration resistance. It adjusts the design response spectrum to reflect how local ground conditions amplify or deamplify shaking.

The wind pressure derived from basic wind speed, exposure, height above grade, topography, and gust effects. Multiplied by pressure and force coefficients, it gives the design pressures applied to building surfaces.

A classification of the terrain roughness and obstruction density around a building - open country, suburban, or urban and wooded. It determines how much the ground surface slows wind at the height of interest.

The moment about a structure's base caused by lateral forces acting at height, which tends to tip the building. It is resisted by foundation and structure weight, anchorage, and the bearing pressure distribution in the soil.

A story markedly less stiff than the stories above it, often because of tall openings or removed infill walls. It draws drift into a single level and makes the building vulnerable to seismic collapse.

A brace whose steel core is encased so that it yields in both tension and compression without buckling. The result is stable, nearly symmetric cyclic behavior and reliable energy dissipation during earthquakes.

Loss of strength and stiffness in saturated granular soil when shaking raises pore water pressure until the soil behaves like a fluid. It can cause settlement, lateral spreading, and failure of foundations and buried utilities.