Tension / Tensile Structures Terminology
Anchor Bolts - Threaded bolts used to
fasten structural members to masonry. Anchor
bolts can be in the form of “J” bolts or
simply a threaded rod. If a threaded rod is
used, there will typically be a nut and a
washer secured to the imbed section of the
bolt to help resist the possibilities of the
bolt being pulled from the concrete.
Anisotropy – The feature of fabric wherein
the physical properties and behavior are not
the same in all directions.
Anticlastic – A surface with positive
(Gaussian) curvature in one principal
direction and negative (Gaussian) curvature
in the other. A saddle shaped surface
Base Fabric – The uncoated fabric, also
known as greige goods.
Bias – Oriented at 45-degrees to the warp
and fill directions of the fabric.
Biaxial – Taken along two concurrent
orthogonal directions, usually principal
Boss Plate – Doughnut-shaped plate
attached to a cable ear plate to reinforce
the pinhole and allow a thinner plate.
Butt Seam – Seam created when the two
pieces being joined are butted together and
joined with a strip twice the width of the
Cable Cuff – Edge treatment in which the
fabric is folded over on itself to form a
pocket in which a catenary cable can be
Cable Fitting – Device attached to the end
of a cable to allow a connection to another
member. Fittings can be swaged, speltered or
Catenary – The curve theoretically formed
by a perfectly flexible, uniformly dense,
inextensible “cable” suspended from each of
two end points. In fabric structures
experience, this shape is probably not ever
truly developed, but is commonly used to
describe the shape developed at the boundary
of a uniformly stressed fabric structure
attached to a cable which is restrained only
at its end points.
Catenary Cable - Steel cables that run
through the pockets on the perimeter of a
tension structure fabric. The shape of the
cable follows that of the pocket, which is
typically curved with a ratio of 1:10. The
length of the cable is to be determined from
by the engineer supplying the fabric
patterning. The thickness of the cable is to
be determined by the engineer who is
calculating the reaction loads at the cable
Catenary Edge – Method of securing the
edge of a panel with a cable tensioned
between two fixed points.
Catenary Pocket (AKA “Banana Pocket”) -
This is the pocket that is placed at the
perimeter of the fabric cover to secure the catenary cable. The pocket has a curve with
a ratio that is defined by the fabric
patterning, but is typically close to a 1:10
ratio. This means for every 10 feet of
length, there will be about a foot of bend
to it. Due to the curvature of the shape,
the pocket is typically fabricated by
sealing together two halves of the pocket
together with an overlap of 1” to 2” at the
outside edge of the pocket.
Clevis – Device used with a cable stud end
or a threaded rod to form a pinned
connection that is somewhat adjustable.
Coating – A material applied to a fabric
for waterproofing and protection of the
Coating Adhesion – Strength of the bond
between the substrate of a fabric and the
Compensation – The operation of shop
fabricating a fabric structure or pieces of
the structure smaller in the unstressed
condition than the actual installed size, to
account for the stretch at pre-stress level.
Crimp – The extent of deformation normal
to the plane of the fabric that the fill and
warp yarns undergo as they are woven
Detension – Relieve the tension or stress
in a membrane.
Elongation – The change in lengths of a
material sample; normally this is associated
with some load or force acting on the
sample. In fabric, this elongation does not
normally refer to true strain of the fiber
elements as in the classical sense; but,
rather, normally refers to the “apparent”
strain resulting from a straightening out of
the crimped yarns in the fabric matrix.
Equilibrium Shape – The configuration that
a tensioned fabric surface assumes when
boundary conditions, pre-stress level, and
pre-stress distribution are defined.
Fabric – A woven or laid cloth made of
Fabric Clamp – Device for clamping the
edge of a fabric panel, usually a bar or
channel shape and made of aluminum or steel.
Fiber – The basic thread of the material
from which the yarns and fabrics are made.
Fill Yarns – The shorter yarns of a
fabric, which usually run at right angles to
the warp yarns. Also known as weft yarns.
Flutter – Excessive, uncontrolled
movement, usually caused by the interaction
between the structure and wind. This occurs
when the fabric lacks sufficient pre-stress.
Footing - The large concrete anchoring
structure that holds the tension structure
securely to the ground. The top of the
footing is typically flush with the ground
level. The footing is comprised of a matrix
of steel rebar that is referred to as a
cage. The concrete is poured into the hole
in the ground that holds the cage. The
anchor bolts get placed into the top of the
footing at their precise location as
indicated in the shop drawings. A certified
engineer must calculate the size of the
footings. The size of the footing must
contain enough weight to hold down the
tension structure for the wind loads in the
Form Finding (AKA "Form Generation") – The
process of determining the equilibrium shape
of a fabric structure.
Greige Goods – Uncoated fabric. Also known
as the base fabric.
Guy Cable - This steel cable is used to
support the structural integrity of the
steel frame. It may be attached at the ends
of the steel struts (or “arms”) to hold them
together and resist them from movement
relative to each other. Unlike catenary
cables, the lengths are calculated by a
straight point-to-point dimension. The
engineer will need to determine the
thickness by calculating the maximum stress
on the cable.
HDPE – High Density Polyethylene (HDPE) fabric is an
extra heavy duty woven mesh fabric that
blocks up to 95% of harmful UV rays.
This superior Fire Rated Knitted shade
fabric is designed for use in modular shade
structures and shade sails.
Hysteresis – The failure of fabric to
return to its original geometry after the
strain-inducing force has been removed.
Keder – Brand name for the solid PVC cord
used at a “rope edge”. Rope edges provide
strength and a surface to evenly distribute
fabric tension forces.
Lap Seam – Seam created when the two
pieces being joined are overlapped by the
width of the seam.
Light Transmission – A measure of the
portion of light striking a fabric surface
that passes through the fabric and into the
space to provide daylighting.
Mast – The principal upright in a tension
Membrane – The fabric panels used in
Membrane Plate – Metal plates attached to
the membrane corners used for securing the
membrane to the frame.
Modulus of Elasticity – The ratio of the
change in stress to the change in strain.
Usually defined as a force per unit width of
a membrane material.
Node Points – Intersection points of the
elements used to define the fabric shape in
the structural analysis; these are normally
given in terms of a three-dimensional
Patterning – The process of defining
two-dimensional pieces of fabric, which can
be spiced together to form a desired
three-dimensional shape. M-Panel is an add
on tool for AutoCAD that has the ability to
assist in the process of patterning.
Poisson’s Ratio – The ratio of lateral
strain to longitudinal strain; may take a
wide range of values due to the deformation
characteristics of a woven material.
pre-stress – The stress state that exists
in a fabric structure when it is not acted
upon by service loads; usually induced by
the boundary conditions of the fabric
PTFE - “Polytetrafluoroethylene”, commonly known by its trademark name Teflon™. This coating is applied to a fiberglass scrim to produce a high strength tension structure fabric membrane with a life expectancy of thirty plus years. PTFE may also be expanded and woven into a fabric that can be coated with a fluoropolymer to create a high strength architectural fabric.
PVC - “Polyvinyl chloride”, properly mixed
with plasticizers for flexibility and
applied to a polyester scrim makes for a
high strength and popular tension structure
fabric membrane. The life expectancy and
cost are proportionally lower than PTFE.
Radius of Curvature – The inverse of the
magnitude of (Gaussian) curvature at a
location on a membrane surface. The
magnitude is typically considered in two
principal directions. The orientation of the
principal directions and their magnitude may
vary continuously over the surface.
Rebar Cage – A reinforcing matrix of steel
rods used to strengthen concrete.
Reinforcement – An additional layer of
fabric placed in an area of high stress to
protect the main fabric.
Roll Goods – Edge treatment in which the
edge of the fabric is folded over on itself
and a rope or cord is incorporated in the
fold to increase the strength of the clamped
Sectionalizing – Method of field joining
large fabric panels utilizing clamping
Sleeve – A tube of fabric, which loosely
contains a structural element such as a
cable, rod, etc.
Spelter – Type of cable fitting in which
the strands of the cable are opened inside
the fitting and molten lead is poured into
the fitting to secure the cable.
Stay Cable – A steel cable that is used to
stabilize the mast in response to the forces
created by wind loads. The stay cables are
used to resist movement of the structure
relative to the earth. One end of the cable
will typically connect to the end of the
steel frame near the fabric connection. The
other end will terminate to a sturdy section
of the mast or a footing in the ground.
Swage – Type of cable fitting in which a
sleeve fits over the outside of the cable
and the sleeve is compressed around the
cable to form a tight fit.
Synclastic – A surface with positive
(Gaussian) curvature in both principal
directions. A bubble shaped surface.
Thimble – Device used in a simple cable
loop end to secure the cable and bear
against the pin. Thimbles are usually used
Top Finish (AKA "Topping") – An additional
coating sometimes used on fabric for greater
protection against UV degradation or for
ease of cleaning purposes (i.e. Ferrari’s PVDF named “T2®”; or Dupont’s PVF named
Turnbuckle – Threaded device used with
cables or rods to allow adjustment.
Ultraviolet (UV) Degradation – The
deterioration of a fabric under long-term
exposure to sunlight. Using a top finish on
the fabric will help prevent the UV
Uniaxial – Taken along one direction,
usually a principal direction.
Warp Yarn – The long straight yarns in the
long direction of a piece of fabric.
Weaving – The process of making a fabric
from yarns passing alternately over and
under each other.
Weft Yarn – The shorter yarns of a fabric,
which usually run at right angles to the
warp yarns. Also called the fill yarns.
Weldment – Connection component, usually
steel, for the attachment of cables and/or
fabric. If may be free-floating or connected
to other membranes.
Wicking – The conveying of liquid by
capillary action along and through the yarns
of the base fabric.
Wire Rope Clip – U-shaped bolt with a
special insert, specifically designed to
clamp a wire rope to itself when forming a
loop end for temporary cables.
Wrinkles – Furrows or ridges on the
normally smooth surface of a fabric
structure, which are indicative of extreme
differences between the principal stresses
typically resulting from a lower stress
perpendicular to the furrow.
Yarn – A number of fibers grouped together
to make a thicker strand for weaving. They
may be twisted together or parallel to each