Class of structure which may be reconfigured, either at installation, or during use. Adaptable Structures are often composed of standard modules.

See Pneumatic Structure.

See Pneumatic Structure.

High pressure Pneumatic structural Component capable of resisting bending. Arch forms are most common but linear columns are also used.

See Pneumatic Structure.

See Isotropic.

An Anticlastic surface has Gaussian Curvature less than zero. Locally, Anticlastic surfaces are Saddle shaped. Most Boundary Tensioned Membrane Structures are composed of Anticlastic surfaces.

Commonly used expession for all structural Components whose bounding volume is significantly larger in one of the three principal axes directions. These include Struts, Ties and some beams and frames.

A Finite Element used to represent an Axial Structural Component.

See Coated Textile.

During Computational Modelling any Axial element capable of resisting bending is termed a Beam Element whatever the name of the physical Component it represents.

In the context of Lightweight Structures the term Biaxial is typically used in connection with the elastic behaviour of the Membrane surfaces. Biaxial Membrane stresses are measured using Biaxial material tests. In some cases Uniaxial tests are also performed.

The traditional sailmaking expression used for a Keder Textile Boundary.

See Boundary.

One of the two main classes of architectural Membrane structures. Unlike Pneumatic structures where Prestress is introduced by air pressure, Boundary Tensioned Membrane Structures are Prestressed by the location of the Boundary.

The terms Boundary and Border are synonomously used to refer to both the complete Boundaries of Tensile surface structural Components, as well as the individual Boundary sections.

A class of structural roofing configuration based on Tensegrity principles. Cable Domes are efficient for wide span applications.

Surface Structures composed of netting fabricated from Cables. Cable Nets are classified as being either Regular or Irregular depending on their mesh geometry. Early Cable Net structures were usually Regular and often waterproofed by cladding with semi-rigid materials. Currently Cable Nets are typically used for zoo aviaries as well as the reinforcement of Pneumatic Cushions.

A flexible Tensile Component usually made from stranded rope.

The pure geometrically defined shape of a Cable or chain hanging under self weight only. Sometimes the expression is, loosely, used to describe any flexible Boundary or Funicular shape.

Although the term Cloth is often used to mean Textile material, it usually refers to the individual pieces of Membrane material from which the Panels of Textile Structure Fields are fabricated.

Unlike most Air Supported Structures which have constant internal pressure, Closed Cell Pneumatic Structures have constant, or close to constant, volume. Accordingly internal pressure varies under applied load.

Most of the materials used for architectural membrane structures are Coated Textiles. These are composed of a woven Base Cloth and a Coating. The most common Base Cloth Textiles are Polyester and Glass. Polyester Textile is usually coated with PVC. Glass Textile is usally coated with PTFE, though Silicon coating is increasing. PVC Coatings ar e often pr otected with a Top Coat or protective Film to increase Dirt Resistance. Materials used include PVDF.

See Coated Textile.

The process of reducing the size of Cutting Patterns so as to introduce the desired level of Prestress. It is usual to perform non-uniform Compensation with the level of Compensation reduced close to the Field Boundary. When this reduction is performed as an additional step, rather than as part of a single Compensation procedure, it is termed Decompensation.

A prefabricated physical object from which a structure is assembled.

A force which shortens a structural member. Depending on the context, the term Compressive can mean carrying Compression, or capable of carrying Compression.

Term given to a variety of numerical mathematical techniques applied to solving the equations that govern fluid flows and aerodynamics.

The process of using computational tools to represent and predict the behaviour of a physical system. Computational Modelling of Lightweight Structures is used for Formfinding, Load Analysis, Cutting Pattern Generation, visualisation, as well as the prediction of environmental behaviour.

The process by which water vapor changes into water droplets.

One of the most common forms of Textile roofs. The term refers loosely to Cone shaped forms and not to pure Euclidean Cones.

State of Stress in a surface where the principal Stresses are uniform at all points. Minimal Surfaces have Constant Stress.

See Adaptable Structure.

In the context of Surface Structures, the term Corner usually refers to the discontinuities in the Boundaries of the Tensile surface Fields. Corners usually require reinforcement or other connection Detailing.

Wind loading pressure coefficients dependent on structural form and local environment. Can be derived from wind tunnel tests but often derived from published data and experience.

The bending of the yarns in a Textile. Weft yarns typically have higher levels of Crimp compared to the Warp. Warp and Weft Crimp is more uniform with Précontraint ® Polyester Textile.

Multiple Layer Pneumatic surface Component, typically used for ETFE roofs and walls.

Process of creating planar patterns for the fabrication of a Doubly Curved Surface Structure.

The layout of the individual Cloth Seams relative to the overall surface Fields. The two most common layouts are, Parallel Layout, and Radial Layout.

See Compensation.

Computational Modelling technique often used during Load Analysis. The Primary Structure is first assumed fully fixed and a Geometrically Non-Linear Load Analysis performed on the Secondary Structure. The Reactions from this analysis are then applied as loads in a conventional rigid frame Load Analysis of the Primary Structure. The technique is only valid when the Primary Structure has low Geometric Non-Linearity.

See Mobile Structure.

See Mobile Structure.

The process of designing the connection and adjustment details, as well as Membrane reinforcements.

Developable surfaces have Gaussian Curvature equal to zero. They may be unrolled, or developed, to a flat state without in-plane deformation. Due to their poor structural behaviourn Developable surface forms are rarely used for stressed Membrane structures.

As air is cooled, its relative humidity (RH) rises until it is saturated and can no longer hold all the moisture in it. The temperature at which this occurs is the Dew Point, and this will vary according to the initial moisture content of the air.

Material property indicating resistance to permanent adhesion of environmental polution. PTFE and ETFE are highly Dirt Resistant whereas PVC is much less so. PVC coated Textile used for architectural applications is therefore usually protected with a Top Coat.

A surface with Gaussian Curvature not equal to zero has Double Curvature.

See Multiple Layer.

Popular method used for the Formfinding, Load Analysis and Cutting Pattern Generation of Lightweight Structures.

See Stiffness.

See Stiffness.

See Finite Element.

Increasingly popular film material made from Ethyl Tetra FluorEthylene. Typically used for Pneumatic Cushion structures.

Surface material fabricated from threads. Most Fabrics used for Lightweight Structures are woven Textile, but non-wovens are also available.

Structurally continuous Tensile Membrane Component bounded by flexible or fixed Boundaries. Fields may be composed of one or more prefabricated Panels.

American name for the Weft of a Textile.

See Foil.

Individual discretisation object of a computational Mesh used for the engineering modelling of structures. Typically elastic link, membrane triangles and bending resistant elements are used.

Process of transforming a Doubly Curved surface (Non-zero Gaussian curvature) to a planar shape. Typically used during Cutting Pattern Generation.

A Mast which, rather than being supported from the ground, is suspended from Ties.

Strictly the term Foil refers to a metalic Membrane. However, it is now the most commonly used term for all Isotropic structural Membranes including the popular ETFE Films.

Popular method used for the Formfinding, Load Analysis and Cutting Pattern Generation of Lightweight Structures.

The ratio of the force in a Link Element divided by its current length. Used in the Computational Modelling of Lightweight Structures with the Force Density method.

State of a structural model where for all degrees of freedom of the Mesh, the summation of internal and external forces acting are zero.

See Cp Factor

The process of determining the Force-Equilibrant Prestress shape.

Force Equilibrant Structure experiencing only Axial forces under Prestress loading.

The Gaussian Curvature

K of a surface is equal to the product of the two principal curvatures k1 and k2,

K = k 1 . k 2

A line across and between two points on a smooth surface where every point’s osculating and tangent planes meet at right angles. When Developed, Geodesic Lines are straight. Commonly mis-defined as being the shortest distance between two points over a surface. Shortest lines are Geodesic, but Geodesic lines need not be shortest. The difference is important because it is the angular, as opposed to the length, aspect of Geodesic lines which make them attractive.

A Cutting Pattern based on Geodesic Seam lines.

Situation where the deflection of the structure must be taken into consideration during Load Analysis. Most Lightweight Structures are Geometrically Non-linear.

Short for Hyperbolic Paraboloid. Note it is not a short form for High Point.

The most typical form of welding used for fabrication of PVC/Polyester Textile Structures.

Commonly used expression for a Radially patterned Conical structure with elevated Mid-Ring.

Simple form of welding which can be used for onsite assembly and repair of PVC/Polyester Textile Structures.

The expression Hypar, derived from Hyperbolic Paraboloid, is commonly used to refer to Saddle shaped surfaces. even those which are not pure Hyperbolic Paraboloids.

See Hypar.

The total luminous flux received on a unit area of a surface. Illuminance is analogous to Irradiance, but Illuminance refers only to light and contains weighting for the wavelength response of the human eye.

The direct, diffuse, and reflected solar radiation that strikes a surface.

A material whose mechanical properties are similar in all directions is termed Isotropic. Conversely if the material’s mechanical properties vary with respect to loading orientation, it is termed Anisotropic. The Coated Textiles typically used for architectural Membrane Structures are strongly elastically Anisotropic, while ETFE Foils are nearly Isotropic.

Encased Cable edge treatment for Membrane surfaces. Either used in conjunction with grooved profile extrusions or with plates, for connection to rigid Boundaries, Corner plates and Boundary Cables.

Aramid yarn material used for high performance composite and Textile Structures. Used for some Textile roof projects in the 1980’s but rarely considered today.

Class of structure covering a broad range of configurations, including many which are bending resistant, and some purely Compressive. Nevertheless the term Lightweight Structure seems to have become mainly associated with Lightweight Tensile Structures.

Modelling assumption often used wherein a Non-Linear relationship is simplified by representing it with a linearly dependent relationship. The linearisation of the non-linear elastic behaviour of materials is a common example.

General term used in Computational Modelling to refer to any Axial Element representing Ties, Struts, Bending resistant Components, as well as Axial Elements representing Textile.

The process of simulating the mechanical behaviour of a structure subjected to a range of applied load cases. Requires Geometrically Non-Linear elastic analysis tools.

Surface coating which is highly reflective to longwave portion of the radiation spectrum, while ideally demonstrating a high transmittance to solar radiation, and in particular to visible light. The term “low-e” is also often used for this type of coating and refers to their Low Emittance in the long-wave infrared range.

A compression support usually located in the interior of a structure.

The Mean Curvature

H of a surface is equal to the arithmetic average of the principal curvatures k 1 and k 2,

H  = (k 1 + k 2)              
              2

Class of structure utilising Biaxially Stressed Membrane Components.

A Surface Structure with no bending resistance and therebye capable of resisting only Tensile forces.

Expression used during the Computational Modelling of structures to describe the connected collection of Finite Elements representing the surfaces and other structural Components.

Usually circular rigid Component employed in the central regions of Conical shaped surface forms.

Minimal surfaces are defined as surfaces with zero Mean Curvature. Usually refers to surfaces of minimum area spanning a specified Boundary. Also commonly used for the minimum energy surfaces enclosing specified volumes, or subject to specified Pneumatic pressure.

A structure which can be moved from location to location. Usually complete or partial dismantling is required.

In order to improve the climatic behaviour of Membrane structures, double or triple Membrane surfaces may be used. The space between the Membranes may be unfilled, filled with insulation, or pressurised.

A Computational Modelling condition where a response can be active or inactive subject to the current configuration. The inability of Tensile materials to carry Compressive forces must be modelled with On-Off Non-Linear Elements.

A material is Orthotropic if it is Anisotropic with the axes of Anisotropy oriented normally. The woven Textiles typically used for Textile architecture have Orthotropic Anisotropy.

The condition of having more Stress in a structure than designed for the long term condition. This is often deliberately planned in order to allow for the relaxation of the Textile.

A prefabricated Tensile Membrane Component composed of Cloths which have been welded or sewn along Seams. Panels may be connected onsite to assemble multi-panel Fields.

One of the most common Cutting Pattern layouts. The seams of the developed Cloths are not strictly parallel, but are “more parallel” than the triangular shaped Cloths created from Radial Pattern Layouts.

See Cutting Pattern Generation.

The process of pulling a Welded Textile Seam apart by out-of-plane loading. Needs to be avoided by careful consideration during the Detailing design phase.

See Temporary Structure.

Process typically used for the determination of structural forms through the use of physical materials. The two main techniques use super-elastic stocking fabric, or soap films. Traditionally used for production Formfinding and Cutting Pattern Generation. Though largely superceded for production design by Computational Modelling, the technique remains appropriate and is widely used at the conceptual design stage.

One of the two main classes of architectural Membrane Structures. Unlike Boundary Tensioned Membrane Structures, where Prestress is introduced by the location of the Boundary, Pneumatic Structures are Prestressed by differential air pressure. Buildings in which the entire inner space is pressurised are termed Airhalls.

Material constant relating the elastic behaviour between orthogonal directions. Sometimes used to model the Crimp interchange behaviour of Coated Textile.

The failure condition where snow, rain or combined loading, causes a local depression to progressively´form in an area of a Membrane surface. Flat horizontal areas are susceptible to this problem.

Proprietary technique used to reduce the elastic Anisotropy of PVC/Polyester material by stressing the Weft yarns during Coating.

The ratio between the Prestress levels in the Warp and Weft directions of a Textile Structure. More generally, the ratio between the principalm Prestress values of a Membrane Structure.

The Stress carried by a structure when subject to no externally applied loading.

The Components of a Tensile Structure are often divided between the Primary and Secondary structures. The Primary Structure is composed of Masts, arches and other semi-rigid supports. The Secondary Structure is composed of the Membrane and associated Cables.

Woven glass Textile coated with PTFE (Poly Tetra Fluor Ethylene). Commonly used for permanent Textile Structures requiring long life.

Woven polyester Textile coated with PVC (Poly Vinyl Chloride). The most commonly used material for fabrication of Textile Structure Membranes. Dirt Resistance can be increased through the use of various Top Coats.

See Coated Textile.

One of the most common Cutting Pattern arrangements typically used for Conical shapes and Pneumatic Structures. The resulting Cloth patterns are typically roughly triangular.

Forces acting on the foundations, or in the case of Decoupled Load Analysis, on the Primary Structure.

The ability of a structure to maintain structural stability following the partial failure of either the Primary or Secondary Structural Components.

Structural configuration composed of surfaces spanned between a series of upper and lower Cables. Resembles a corrugated fan.

Common general expression for Anticlastic architectural surfaces which are neither Conical nor Ridge and Valley shaped.

The ratio of the sag to the chord length of a Boundary cable expressed as a percentage.

Expression commonly used in architectural contexts to describe stressed Textile Structures. Though common, it is somewhat misleading as the sails of boats are stabilised by normal air pressure. This sometimes leads to the inappropriate specification of triangular Textile Structures.

Architectural term used to describe a Boundary composed of multiple Cables, due to the resemblance to a scallop seashell.

Linear connection between individual Cloths of a Membrane Structure. Usually made by welding, but in some cases still by sewing or glueing.

See Primary Structure.

The cross sectional geometric properties of a structural member used during Load Analysis.

See Cp Factor.

Surface structure with bending resistance. The Textile and Foil materials used for most Tensile Structures have negligible bending stiffness and therefore behave as Membranes. Sometimes the term Shell is loosely used in architectural contexts to describe Tensile Membrane Sructures which are not structural Shells.

Woven glass Textile coated with silicon. Still less used than PVC/Polyester or PTFE/Glass, Silicon/Glass is increasingly popular.

The equivalent temperature of the clouds, water vapor, and other atmospheric elements making up the sky to which a surface can radiate heat.

Physical Modelling technique used to determine Constant Stress forms by exploiting the energy minimising behaviour of soap films.

Pressure-driven airflow produced by convection as denser cool air sinks and forces warm air to rise, creating a positive pressure at the top of the building and a negative pressure area at low level.

A Tensile support Component usually connecting a Boundary Corner to the foundations.

In general engineering, the material constant used to represent Stiffness is Young’s Modulus E. E is defined as the ratio between the Stress and Strain of an elastically linear material. Due to the complex microstructure of the Coated Textile and rope materials typically used for Tensile Architecture, Stiffness is more usually measured and specified together with the cross sectional area. The combination of the material Stiffness constant E with the area A is referred to as the EA Value. In the case of Textile, EA values are specified for a unit width.

Ratio of the extension under load of a structural member to the unstressed length.

The usual engineering definition for Stress is force per unit area. Due to the complex non-uniform nature of the Coated Textile materials used for Tensile architecture, Textile Stresses are usually expressed as force per unit width.

An Axial structural Component capable of resisting both Tensile and Compressive forces.

See Primary structure.

The process in which a heat flux is exchanged between a surface and the adjacent air layer.

A structure composed of Membrane, Shell or Cable Net structural Components.

A Tensile support Component usually connecting a Mast top to the Secondary Structure. The term is used for a broader range of components than in the field of bridge engineering.

A Synclastic surface has Gaussian Curvature greater than zero. Locally, Synclastic surfaces are dome shaped. Pneumatic Structures are composed of either exclusively Synclastic surfaces, or combinations of Synclastic and Anticlastic surfaces.

The Computational Modelling of Tensile Structures is performed using the geometry of the various structural Component centre lines. This is termed the System Line geometry and is further processed during the Detailing design phase to provide the final production Component geometries.

The legislative procedures for the realisation of structures which are Permanent are significantly different to those applying to structures which are Temporary. The distinction between the two situations will greatly affect the resulting design.

Name derived from the words Tension + Integrity by R Buckminster Fuller to describe a class of truss structures discovered by K Snelson. In a pure Tensegrity truss all structural Components are either Struts or Ties, and no Strut connects directly to any other. Tensegrity principles are popular in two main ways. They can offer high structural efficiency for wide span applications such as with the Cable Dome. They also offer interesting aesthetic possibilities. In practice, applications of Tensegrity structures are rarely pure and incorporate ring beams and Membrane cladding.

Class of structural configurations where most of the structural Components experience only Tensile forces.

A force which lengthens a structural member.

Fabric material usually woven from orthotropic oriented yarns.

One of the basic mechanisms for energy transfer between regions at different temperatures, radiation is the emission of energy by the flux of an electromagnetic field. The net radiative energy exchange between a surface and its surroundings is the difference between the thermal radiation received and emitted by the surface. Unlike convection and conduction, radiation does not rely on an intermediate material medium and the energy transfer is effectively instantaneous.

Thermal property that expresses the amount of energy transferred by combined heat transfer coefficients at both surfaces and conducted through a material as the result of a temperature difference of 1°C between the air temperatures at the two sides. Its value is expressed in W/m

2K. The thermal transmittance, often referred to as the U-value, is widely used in the construction industry to define the rate of heat transfer through building constructions.

The most typical type of welding used for fabrication of PTFE/Glass Textile Structures as well as of ETFE Foil Membrane Structures.

An Axial structural Component capable of resisting Tensile but not Compressive force or bending.

See Coated Textile.

The degree to which diffused light can pass through a material.

Device composed of a doubly threaded cylinder commonly used to provide length adjustment of Cables.

See Thermal Transmittance.

See Constant Stress.

See Biaxial.

See Ridge and Valley.

The ratio between the Stress levels in the Warp and Weft directions of a Textile Structure.

The yarns running lengthwise and parallel to the selvage in a woven Textile.

Woven flat strip material used for reinforcing Textile Structures. Popularly used as an alternative to steel rope for the Boundaries of small structures.

The filling yarns running perpendicular to the Warp yarns.

The flow of a liquid into a Textile through the yarn due to capillary action at unsealed edges.

Puckered or creased Membrane surface condition. May occur when Biaxial Tensile stressing is not achieved during installation, or subsequently following Textile relaxation.

See Stiffness.

A developable surface.