A term for force, adopted for the Eurocodes. This implies movement but in the case of a structure is generally intended to remain static.


A horizontal member that carries vertical loads along its length. It can be made out of timber reinforced concrete, steel or aluminium.

Bending moment

The bending force in, for example, a beam. The units of bending moment are those of force x distance, for example, kiloNewton-metres.


Computer Aided Design: A term applied to systems or techniques for design and drafting that utilize integrated computer hardware.


Overhanging beam, roof or floor.

Civil engineering

Civil engineering is a professional engineering discipline that deals with the design, construction, and maintenance of the physical and naturally built environment, including works like roads, bridges, canals, dams, and buildings.


The seperately-applied exterior finish of a framed building.


A vertical member designed to resist axial load (direct compression), such as the weight of a building. May be made of any suitable material such as concrete, masonry, steel or timber. Design is governed by the slenderness (ratio of length to breadth) to resist the tendency to fail by buckling.


An axial force in the "pushing" or "squashing" sense; the opposite of tension. Columns are designed to resist compression, but it is also produced in bending of beams.

Continuous Beam

A beam with more than two points of support.

Dead Load

The force on a structure resulting from the weight of the structure itself. This is normally constant, except of course during construction or demolition when the changes in load need to be considered to ensure safety at each stage.


The change in shape resulting from the application of a force or load. Beams deflect due to bending, even when made of steel or concrete. Limiting deflection to an appropriate value is often the governing consideration in design of buildings, to ensure serviceability in use. Bouncy floors, sticking doors, leaky roofs and cracked finishes are symptoms of excessive deflection.


Deformation in continuum mechanics is the transformation of a body from a reference configuration to a current configuration. A configuration is a set containing the positions of all particles of the body.

Design check

Evaluation of the design to determine whether it conforms with the design brief and can be expected to provide a safe engineered solution.

Factor of Safety

A figure by which the design strength of a structure is reduced (or the design load increased) in order to ensure the structure has a reserve of strength against failure or collapse. This is intended to cater for variations in material strength or uncertainties in determining the design load.

Finite Element Analysis FEA Method

The finite element method (FEM) is a numerical technique for finding approximate solutions to boundary value problems for partial differential equations. It is also referred to as finite element analysis (FEA).


Fundamental to engineering science, an influence that causes a body to change its speed, direction or shape. Structures are usually intended to resist movement, so the effect of the force is to change the shape of the structure, causing deflection. The stiffness of the structure determines the amount of deflection for a given force.

Imposed Load

The load imparted to a structure by the objects that it supports, such as people, furniture, vehicles and so on. Other imposed loads are caused by snow on roofs, for example.


A structural steel section shaped like an I, such as a Universal Beam.

Live Load

Another term for Imposed Load.


A measure of force causing a turning effect due an offset distance between the line of action and reaction. This is used to assess problems of bending in beams, or overturning in structures such as retaining walls or dams. A moment is calculated by multiplying the force by the length of the "lever arm" perpendicular to the direction of the force, hence its unit: newton metres (Nm).

Permissible stress

Stress that can be sustained safely. Codes of Practice for structural design used to specify permissible stresses with which the actual stress was to be compared.


A column or pillar in Architecture and Structural engineering is a structural element that transmits, through compression, the weight of the structure above to other structural elements below. In other words, a column is a compression member.

Plate theory

In continuum mechanics, plate theories are mathematical descriptions of the mechanics of flat plates that draws on the theory of beams. Plates are defined as plane structural elements with a small thickness compared to the planar dimensions.


Sloping structural member supporting a roof.

Rigid frame

A rigid frame in structural engineering is the load-resisting skeleton constructed with straight or curved members interconnected by mostly rigid connections which resist movements induced at the joints of members. Its members can take bending moment, shear, and axial loads.


The distance between the centres of supports for a beam or truss. This is greater than the width of the opening but less than the length of the beam. Where spans are quoted in design calculations this should not be taken as the length of the beam.


The condition of a structure or a mass of material when it is able to support the applied stress for a long time without suffering any significant deformation or movement that is not reversed by the release of the stress.


Statics is the branch of mechanics that is concerned with the analysis of loads (force and torque, or "moment") acting on physical systems that do not experience an acceleration (a=0), but rather, are in static equilibrium with their environment.

Steel building

A steel building is a metal structure fabricated with steel for the internal support and for exterior cladding, as opposed to steel framed buildings which generally use other materials for floors, walls, and external envelope.


Is the measure of internal force within a body, defined as the amount of force per unit area.

Structural analysis

Structural analysis is the determination of the effects of loads on physical structures and their components.

Structural Engineering

A branch of engineering dealing with structures, such as buildings and bridges.

Structural glass

Glass used in situations where it will or may support more than just its own weight. Glass balustrades, stairs and floor panels are becoming common.

Structural load

Structural loads or actions are forces, deformations, or accelerations applied to a structure or its components.

Loads cause stresses, deformations, and displacements in structures. Assessment of their effects is carried out by the methods of structural analysis.

Structural steelwork

A frame of steel sections supporting other parts of the structure

Structural system

The term structural system or structural frame in structural engineering refers to load-resisting sub-system of a structure. The structural system transfers loads through interconnected structural components or members.


In engineering, a truss is a structure that "consists of two-force members only, where the members are organized so that the assemblage as a whole behaves as a single object".

A "two-force member" is a structural component where force is applied to only two points.

Ultimate Limit State

(ULS) The condition in which the factored loads are compared with the capacity of the structure. The working loads are multiplied by factors so as to provide a margin of safety against failure, as opposed to the allowable stress method which reduces the calculated strength to compare with the working loads.

Young's modulus

A measure of the elasticity of a material. Defined as stress divided by strain; see modulus of elasticity.