Tension member

A tension member is a structural element designed to carry loads primarily through tensile forces, meaning it is subjected to stretching rather than compression or bending. These members are integral components in engineering and architectural structures, such as trusses, bridges, towers, and suspension systems, where they provide stability, distribute loads, and resist deformation. Typically made from high-strength materials like steel, wire ropes, or composites, tension members are valued for their efficiency in transferring forces along their length while maintaining lightweight and durable construction. Their design and performance are crucial in ensuring the safety and functionality of structures subjected to dynamic and static loads.

Designers typically adhere to standardised design codes when specifying tension members, which are critical components of structural systems. In the United States, the Steel Construction Manual published by the American Institute of Steel Construction (AISC) is the primary reference for structural steel design, while in Europe, the design is guided by the Eurocodes published by the Comité Européen de Normalisation (CEN). These codes provide comprehensive guidelines to ensure the safety, reliability, and efficiency of tension member designs. Other similar design codes are: GB 50017 in China, IS 800 in India and AS 4100 in Australia.

The design of tension members requires careful analysis of potential failure modes, specifically yielding (excessive deformation) and fracture, which are referred to as limit states. The governing limit state is the one that results in the lowest design strength, as it dictates the member's capacity and prevents structural failure.

There are two primary methods for evaluating the capacity of a structure and its components to withstand applied loads: Load and Resistance Factor Design (LRFD) and Allowable Stress Design, sometimes referred to as Permissible Stress Design. This section provides an overview of calculations using the LRFD method for tension members in steel structures.

According to the Australian code, the nominal section capacity of a tension member is the lesser of -

${\displaystyle N_{t}=A_{g}f_{y}}$ and;

${\displaystyle N_{t}=0.85k_{t}A_{n}f_{u}}$

Where: