Tension members are structural elements that are subjected to axial
tensile force
In physics, tension is described as the pulling force transmitted axially by the means of a string, a rope, chain, or similar object, or by each end of a rod, truss member, or similar three-dimensional object; tension might also be described as t ...
s. Examples of tension members are bracing for buildings and
bridge
A bridge is a structure built to span a physical obstacle (such as a body of water, valley, road, or rail) without blocking the way underneath. It is constructed for the purpose of providing passage over the obstacle, which is usually somethi ...
s,
truss
A truss is an assembly of ''members'' such as beams, connected by ''nodes'', that creates a rigid structure.
In engineering, a truss is a structure that "consists of two-force members only, where the members are organized so that the assembl ...
members, and
cable
Cable may refer to:
Mechanical
* Nautical cable, an assembly of three or more ropes woven against the weave of the ropes, rendering it virtually waterproof
* Wire rope, a type of rope that consists of several strands of metal wire laid into a hel ...
s in suspended
roof
A roof ( : roofs or rooves) is the top covering of a building, including all materials and constructions necessary to support it on the walls of the building or on uprights, providing protection against rain, snow, sunlight, extremes of te ...
systems.
Calculation
In an axially loaded tension member, the stress is given by:
F = P/A
where P is the magnitude of the load and A is the cross-sectional area.
The stress given by this equation is exact, knowing that the cross section is not adjacent to the point of application of the load nor having holes for bolts or other discontinuities. For example, given an 8 x 11.5 plate that is used as a tension member (section a-a) and is connected to a
gusset
In sewing, a gusset is a triangular or rhomboidal piece of fabric inserted into a seam to add breadth or reduce stress from tight-fitting clothing. Gussets were used at the shoulders, underarms, and hems of traditional shirts and chemises made ...
plate with two 7/8-inch-diameter bolts (section b-b):
The area at section a - a (gross area of the member) is 8 x ½ = 4 in
2
However, the area at section b - b (net area) is (8 – 2 x 7/8) x ½ = 3.12
in2
knowing that the higher stress is located at section b - b due to its smaller area.
Design
To design tension members, it is important to analyse how the member would fail under both yielding (excessive deformation) and fracture, which are considered the limit states. The limit state that produces the smallest design strength is considered the controlling limit state. It also prevents the structure from failure.
Using
American Institute of Steel Construction standards, the ultimate load on a structure can be calculated from one of the following combination:
1.4 D
1.2 D + 1.6 L + 0.5 (L
r or S)
1.2 D + 1.6 (L
r or S) + (0.5 L or 0.8 W)
1.2 D + 1.6 W + 0.5 L + 0.5 (L
r or S)
0.9 D + 1.6 W
L= 14
* D… is the dead load or the weight of the structure itself
* L… is the live load which vary for different structures
* S… is the snow load
* W… is the wind load
the central problem of designing a member is to find a cross section for which the required strength doesn't exceed the available strength:
P
u < ¢ P
n where P
u is the sum of the factored loads.
to prevent yielding
0.90 F
y A
g > P
u
to avoid fracture,
0.75 F
u A
e > P
u
therefore, the design must consider the loads applied to this member, the design forces acting on this member (M
u, P
u, and V
u) and the point where this member would fail.
See also
*
Compression member
Compression members are structural elements that are pushed together or carry a load; more technically, they are subjected only to axial compressive forces. That is, the loads are applied on the longitudinal axis through the centroid of the mem ...
References
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Arches and vaults