The most used engineering terminology can be confusing to the average consumer. Understanding the common jargon used in structural engineering can help you communicate with your architect, engineer, or construction manager more effectively.
A structural member, usually horizontal, with a main function to carry loads cross-ways to its longitudinal axis. These loads usually result in bending of the beam member. Examples of beams are simple, continuous, and cantilever. Beams, girders, joists, and headers all work together to transfer loads from floor and roof systems into columns. See the blue members labeled “A” in the figure below.
This is a structural member whose main function is to carry loads in both bending, like a beam, and tension/compression, like a column.
Bearing stress acts in a direction normal to the axis of the beam and does not add to the normal stresses from compression and bending. These stresses are a resultant of the beam bearing on a support and are checked locally on the beam because the stresses do not radiate significantly throughout the beam.
Bending stress is a resultant of vertical or horizontal loading on a beam. This type of loading creates a compressive and tensile stress.
Bending shear stress is the resultant of vertical or horizontal loading. When the beam is loaded the fibers throughout the beam are elongating and contracting through each layer of the beam from the normal stresses, this difference in elongation creates a shear stress that transfers through each layer of the beam.
Related to deflection a Camber is designing a member with opposing deflection so that when loaded the member has smaller or no deflection than without the camber.
Much like a swimming pool diving board, cantilever simply refers to the part of a member that extends freely over a beam, which is not supported at its end. The most left span, Span 1, of the below figure is a cantilevered end of a beam.
A column is a main vertical member that carries axial loads in compression from other framing members to the foundation parallel to its longitudinal axis. See the green members labeled “B” in the figure below.
Continuity is used to define the transfer of internal and external loads and stresses from member to member as if there were no connections.
Damping is the rate of decay of amplitude for floor vibrations.
Dead load describes the loads from the weight of the permanent components of the structure.
Deflection is the displacement of a structural member or system under a load. Building codes allow for different amounts of deflection for different building systems.
This type of load varies over time.
A footing is a slab of concrete under a column, wall, or other structure to transfer the loads of the member into the surrounding soil. This is the final step in the load path, transferring vertical loads into the ground. See the gray rectangular blocks labeled “C” in the figure below.
A foundation is a concrete element used to support the structure and transfer all the loads into the ground.
A type of Joist Girder using joists located at panel points where diagonal webs intersect the top chord of the joist only.
A gable is the term used when a roof slopes down only 2 sides then has a front or back that is higher than the sloped roof.
Gage or sometimes spelled “Gauge” is the term used to define the thickness of a sheet material. It can also be used to define the spacing between holes or amount of workable area on a member.
A girder is a horizontal member which directly loads into main supports and connects beams and floor systems to the vertical supports. See the thicker red members labeled “D” in the figure below.
A type of engineered lumber that allows for larger size beams, girders, and columns while using smaller trees. Glulam stands for Glued-Laminated Timber.
This can refer to two things: for common construction work, it refers to the ground elevation. However, for structural engineering specifics it may be referring to the material grade. The material grade is most commonly used for steel members, such as A992 or A36.
A member that carries other supporting members and is placed between other beams. An example of a header is a short LVL beam over an extra large doorway.
A roof that slopes downward on all sides of the building. These are used more in snowy or high wind areas.
A joist is a member, similar to a beam but instead of one solid member, joists are multiple pieces joined together to create a lighter alternative to a beam. Joist can be open-web or wood “I” shapes created from engineered lumber. Joists are designed as simply supported beams. See the thin black closely spaced members labeled “E” in the figure below.
A kip is equal to 1000 pounds. It is used most frequently when talking about point loads, building weights, or base shear values.
Loading of a member describes what types of forces the member will be subjected to during construction and occupation of the structure. There are many different types of loading conditions and most do not occur alone. This section describes the different types of loading conditions as well as a brief explanation of building code prescribed load combinations.
A force applied to any member of the structure or the structure itself. For structural engineering purposes a load can be categorized in a few different ways, each of these categories is listed below and used in Load Combinations.
An area load, typically expressed in psf (lbs/ft^2), is a load that is spread over an entire region. Most of the time these loads are used for floor systems and different areas of the building.
A load type that includes the additional dead loads (not the weight of people and not the weight of the building itself), such as plumbing, duct work, ceilings, and other components of the structure. Typically, this load is about 5 psf.
A dead load is a static load applied by the permanent weight of the structure and its components.
A load that acts along a single distance or span of a member, typically expressed in plf (lbs/ft). A distributed load can be evenly distributed along the member or vary along it’s length. Span 1 in the figure above is loaded with a uniformly varying Distributed load, where Span 2 is loaded with a uniform Distributed load.
A load type that changes over time. Dynamic loads are used during a dynamic analysis of a structure. Wind and Seismic loads are dynamic but are used in both static and dynamic analysis.
A live load is described as any load that is not permanent to the structure. This means it could be occupancy of specific areas or specific equipment used for the building occupants.
A point load is expressed in pounds (lbs) or kips (k) and is described as a single amount of force applied at a single point. Area Loads or Line Loads can be converted to a single point load by multiplying by the area or distance the load acts on. Span 3 in the figure above is loading with a single point load.
A live load that occurs only at the roof level, typically this is around 20 psf.
A load that occurs during roof flooding.
A load that is applied to the structure due to the ground movements during an earthquake. Typically, these loads are applied in the horizontal direction, as indicated in the figure.
A load that occurs due snow accumulation and drifts on the roof.
A load type that does not change over time, which includes loads like Dead, Live, Roof Live, Rain, Snow, as well as Equivalent Wind and Seismic.
A load applied perpendicular to the member which causes a twisting motion in the member about its longitudinal axis. A couple or moment in a plane perpendicular to the axis produces simple torsion.
A load applied to the structure due to wind pressures. While the wind pressure itself is not a static load, we treat it as one for simplicity of analysis.
Load combinations are used to create loading conditions with multiple loads acting on the structure or one of its’ components, but factored to account for the statistical likelihood of them happening together.
This is the how the loads are carried through the structure, providing a continuous load path to the ground is the structural engineer’s most important job.
Named Young’s Modulus, the Modulus of Elasticity is the slope of the straight line in the elastic region of a stress-strain graph. For structural steel used in most building applications, the Modulus of Elasticity is equal to 29,000 ksi (kips per square inch).
Moment is the tendency of a force to cause a rotation about a point or axis which in turn produces bending stresses.
A moment connection carries shear and moment, it can also be called a fixed connection. This connection is used in most lateral force resisting system (LFRS) frames. Support C in the figure below is a moment connection with its’ three reactions, vertical horizontal, and moment.
A measure of the resistance to rotation offered by a member’s geometry and size.
The normal stress in a beam is resultant from axial loading. This type of loading is a compressive or tensile force that acts through the centroid of the section. Although the normal stress can be uneven through the cross section of the beam near the points of loading it is usually taken as an average in the stress calculation.
A pin connection only carries shear forces to the reaction. Pin connections are the most common connection in repetitive framing. Support B in the figure below is a pin connection with two reactions, a vertical and horizontal force.
Pitch is the slope of a member defined as the ratio of the total rise to the total width. The pitch is most commonly used to describe the slope of a roof system.
A Distributed Load acting on a member in plf (lb/ft). The two line loads shown in the figure would be expressed as this unit type.
An Area Load acts on an area in psf (lb/sq ft).
A reaction is the force and/or moment that occurs at a support. When transferring forces from member to member the reaction force is the force that is transferred. At each support in the figure below, the reactions at each different support type are shown as pink arrows.
Shear forces can most easily be described as forces acting opposite and parallel to one another. These forces cause sliding between the two materials or members, which can act in the vertical (Pin Connection) and horizontal direction (Shear Wall).
A member at which one end is a pin connection and the other a roller connection. This is the most common member type. Span 2, the middle span of the figure, if by itself would be a simply supported beam.
A concrete floor or roof system, typically these range from 3-8 inches in thickness.
The distance from one support to the other for a single member.
The slope of a force-displacement graph, the stiffness of a member describes its resistance to deformations.
Steels suitable for load-carrying members in a structure.
A strut is part of a brace that is used to resist tension and compression forces.
A stud is a 2x dimensional lumber or cold-formed steel used vertically for wall framing. Studs are spaced anywhere from 16 inches on center to 24 inches on center. At the ends of walls sometimes studs are doubled up and can be called a “King Stud”.
Torsional shear stress is the resultant of a torque on the beam. When torque is applied to the beam each cross section is experiencing this shear stress in the plane of the cross-section.
One stress that is not commonly accounted for in general beam design is the warping stress. This stress occurs when a torque is applied to a non-circular beam where the cross section of the beam will warp out of the plane and cause normal and shear stresses throughout the affected section.
These most used structural engineering terminology definitions provide a baseline understanding of engineering jargon for the average consumer and new students. If you’d like to learn more about structural engineering topics, browse the rest of our blog.
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