Can temperature changes alter guy-wire tension?

The short answer

Yes. Temperature changes can alter the cable’s unstressed length and the positions of its supports, changing tension in a restrained system. The direction and magnitude depend on relative thermal movement, stiffness and geometry. A tension measured at one temperature should therefore not automatically be compared with a value specified for another condition.

Separate free expansion from restrained force

An unconstrained cable can change length with temperature without developing a large additional axial force. In a guyed tower, the cable is restrained by the tower and anchor geometry, so some thermal change can appear as tension change or structural movement.

If cable and supporting structure move together in compatible ways, the effect can differ from a model with perfectly fixed endpoints. Cooling does not justify a universal tension adjustment rule for every tower.

Include the real thermal and structural conditions

The cable, tower and ground need not share one temperature. Sun exposure, wind and shading can create different component temperatures, while anchor movement or sag affects the equilibrium further.

Record the applicable reference temperature and the measurement conditions when comparing tension evidence. A nominal ambient reading may be useful context but is not always the temperature of every structural component. Apparent disagreement can reflect different conditions rather than a loose or damaged cable.

Use the tower designer’s temperature basis

The structural assessment should define the relevant thermal cases and how tension limits or installation targets apply. Any measurement or adjustment procedure must belong to that assessed tower, cable and anchor arrangement.

Do not retension guys merely because a seasonal reading differs from an old record. First establish comparability and assess consequences for tower compression, anchors and directional stiffness. OpenFAST theory explains thermal initial-strain and pretension mechanics; it does not provide a temperature correction, tension target or field adjustment instruction for MARSTON installations.