Comprehensive Guide to Structural Engineering Terms & Definitions

Understanding the Importance of Structural Engineering Terminology

Essential Structural Engineering Terms Explained

Navigating the world of structural engineering can be daunting with its intricate terminology. But fear not! Whether you’re a budding engineer, an architecture enthusiast, or simply curious, we’ve broken down the most essential terms for you.

Dive in to demystify the jargon and gain a clearer understanding of the foundational concepts that shape our built environment.

Beam: The Backbone of Structures

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.

Beam-Column: Where Beam Meets Column

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: Distributing Forces

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 Normal Stress: Responding to External Forces

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: The Internal Resistance

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.

Camber: The Upward Curve in Beams

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.

Cantilever: The Unsupported Overhang

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.

Column: The Vertical Support Pillar

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: Uninterrupted Connection in Structures

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: Energy Dissipation in Structures

Damping is the rate of decay of amplitude for floor vibrations.

Dead Load: Permanent Weight on Structures

Dead load describes the loads from the weight of the permanent components of the structure.

Deflection: The Bending or Deformation Response

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.

Dynamic Load: Varying Forces Over Time

This type of load varies over time.

Footing: The Base Support of Structures

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.

Foundation: The Groundwork of Buildings

A foundation is a concrete element used to support the structure and transfer all the loads into the ground.

G-Type Joist Girder: Specialized Support Systems

A type of Joist Girder using joists located at panel points where diagonal webs intersect the top chord of the joist only.

Gable: The Triangular Roof Section

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: The Thickness Measurement

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.

Girder: The Main Horizontal Support

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.

Glulam: Glued Laminated Timber

A type of engineered lumber that allows for larger size beams, girders, and columns while using smaller trees. Glulam stands for Glued-Laminated Timber.

Grade: Quality Classification of Materials

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.

Header: The Framing Element Above Openings

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.

Hip Roof: Sloping on All Sides

A roof that slopes downward on all sides of the building. These are used more in snowy or high wind areas.

Joist: The Horizontal Support Members

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.

Kip (k): A Unit of Force

A kip is equal to 1000 pounds. It is used most frequently when talking about point loads, building weights, or base shear values.

Diving into Types of Loads in Structural Engineering

Every edifice, from majestic high-rises to quaint cottages, endures the push and pull of various external and internal forces. These forces, termed as loads, are the backbone of structural stability and design.

In the realm of structural engineering, grasping the nuances of these loads is paramount for the resilience and safety of a structure. Let’s embark on a journey to unravel the multifaceted nature of loads and their significance in shaping our built environment.

Loading: Applying Forces to Structures

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.

Load: Forces Acting on Structures

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.

Area Load: Distributed Forces Over a Surface

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.

Collateral Load: Additional Non-Occupancy Weight

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.

Dead Load: Permanent Weight of Structures

A dead load is a static load applied by the permanent weight of the structure and its components.

Distributed Load: Forces Spread Over Length

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.

Dynamic Load: Forces Changing Over Time

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.

Live Load: Temporary Weight on Structures

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.

Point Load: Specific Force at a Point

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.

Roof Live Load: Temporary Roof Weight

A live load that occurs only at the roof level, typically this is around 20 psf.

Rain Load: Weight from Rain Accumulation

A load that occurs during roof flooding.

Seismic Load: Earthquake-Induced Forces

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.

Snow Load: Weight from Snow on Roofs

A load that occurs due snow accumulation and drifts on the roof.

Static Load: Unchanging Forces on Structures

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.

Torsion Loads: Twisting Forces on Members

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.

Wind Load: Forces from Wind Pressure

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.

Expanding Your Knowledge in Structural Engineering

The world of structural engineering is vast, intricate, and ever-evolving. As the backbone of our urban landscapes, it intertwines science, art, and innovation to create safe, functional, and aesthetically pleasing structures. Delving deeper into this discipline reveals a myriad of concepts, methodologies, and breakthroughs that have shaped our modern world.

Whether you’re a budding engineer, an architecture enthusiast, or simply curious, broadening your understanding of structural engineering can offer fresh perspectives on the built environment around you. Dive in, explore its depths, and discover the marvels of engineering that stand tall against time and nature.

Load Combinations: Combining Different Load Types

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.

Load Path: Ensuring Continuous Force Transfer

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.

Modulus of Elasticity (E): Material’s Stiffness Measure

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: The Rotational Force

Moment is the tendency of a force to cause a rotation about a point or axis which in turn produces bending stresses.

Moment Connection: Joining Members to Resist Rotation

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.

Moment of Inertia (I): Resistance to Rotation

A measure of the resistance to rotation offered by a member’s geometry and size.

Normal Stress: Axial Stress in Members

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.

Pin Connection: Simplified Support Mechanism

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: Describing Slope of Members

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.

Pounds per Linear Foot (plf): Measuring Distributed Loads

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.

Pounds per Square Foot (psf): Measuring Area Loads

An Area Load acts on an area in psf (lb/sq ft).

Reaction: Forces at Supports

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 Acting Parallel and Opposite

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).

Simply Supported: Basic Beam Support Mechanism

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.

Slab: Concrete Floor or Roof System

A concrete floor or roof system, typically these range from 3-8 inches in thickness.

Span: Distance Between Supports

The distance from one support to the other for a single member.

Stiffness: Resistance to Deformations

The slope of a force-displacement graph, the stiffness of a member describes its resistance to deformations.

Structural Steels: Metals for Load-Carrying Members

Steels suitable for load-carrying members in a structure.

Strut: Part of a Bracing System

A strut is part of a brace that is used to resist tension and compression forces.

Stud: Vertical Wall Framing

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: Resultant of Torque

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.

Warping Stress: Stress from Non-Circular Beam Torque

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.

Dive Deeper into Structural Engineering

Structural engineering is more than just beams, columns, and load calculations; it’s a symphony of science and creativity that brings buildings to life. As you delve further into this captivating field, you’ll uncover layers of complexity, from the intricacies of material science to the art of sustainable design. Each project is a puzzle, challenging engineers to balance aesthetics, functionality, and safety.

By diving deeper, you’ll gain a profound appreciation for the silent guardians—bridges that connect cities, skyscrapers that touch the clouds, and homes that shelter families. So, take the plunge and immerse yourself in the fascinating world of structural engineering, where every structure has a story waiting to be told.

Expanding Your Knowledge

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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