Tension member

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Tension members are structural elements that are subjected to axial tensile forces. Examples of tension members are bracing for buildings and bridges, truss members, and cables in suspended roof systems.

Bridge structure built to span physical obstacles

A bridge is a structure built to span a physical obstacle, such as a body of water, valley, or road, without closing the way underneath. It is constructed for the purpose of providing passage over the obstacle, usually something that can be detrimental to cross otherwise. There are many different designs that each serve a particular purpose and apply to different situations. Designs of bridges vary depending on the function of the bridge, the nature of the terrain where the bridge is constructed and anchored, the material used to make it, and the funds available to build it.

Truss structure that consists of two-force members only

A truss is an assembly of beams or other elements 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 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. Although this rigorous definition allows the members to have any shape connected in any stable configuration, trusses typically comprise five or more triangular units constructed with straight members whose ends are connected at joints referred to as nodes.

Wire rope rope made from wire

Wire rope is several strands of metal wire twisted into a helix forming a composite "rope", in a pattern known as "laid rope". Larger diameter wire rope consists of multiple strands of such laid rope in a pattern known as "cable laid".

Contents

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 plate with two 7/8-inch-diameter bolts (section b-b):

Gusset piece of fabric

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 of rectangular lengths of linen to shape the garments to the body.

The area at section a - a (gross area of the member) is 8 x ½ = 4 in2

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:

American Institute of Steel Construction

The American Institute of Steel Construction (AISC) is a not-for-profit technical institute and trade association for the use of structural steel in the construction industry of the United States.

1.4 D

1.2 D + 1.6 L + 0.5 (Lr or S)

1.2 D + 1.6 (Lr or S) + (0.5 L or 0.8 W)

1.2 D + 1.6 W + 0.5 L + 0.5 (Lr or S)

0.9 D + 1.6 W

L= 14

the central problem of designing a member is to find a cross section for which the required strength doesn't exceed the available strength:

Pu < ¢ Pn where Pu is the sum of the factored loads.

to prevent yielding

0.90 Fy Ag > Pu

to avoid fracture,

0.75 Fu Ae > Pu

therefore, the design must consider the loads applied to this member, the design forces acting on this member (Mu, Pu, and Vu) and the point where this member would fail.

See also

Related Research Articles

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Most of the terms listed in Wikipedia glossaries are already defined and explained within Wikipedia itself. However, glossaries like this one are useful for looking up, comparing and reviewing large numbers of terms together. You can help enhance this page by adding new terms or writing definitions for existing ones.

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References