Preventing Rope Sag: Maintenance and Tensioning Solutions

Rope sag is a problem that starts off harmless enough and slowly turns into a major one. Apart from looking unprofessional and untidy, an unstretched rope reduces the overall structural stability of the installation, creates a tripping hazard, allows movement in load bearing applications and in some cases, stresses the anchor points.

However, sag can be easily prevented, as understanding the reasons behind loss of tension of the rope makes it possible to easily control it.

Why Cables and Ropes Lose Tension

It's natural to expect that once the correct tension is established, it will remain constant throughout time. However, this is not the case, as there are several factors that work against it.

Stretch is the most common reason for the loss of tension. The steel rope is elastic, and when subjected to a load, it elongates. Although this is the normal state of affairs, this means that the installation usually requires re-tensioning after the initial period of time passes.

Thermal expansion/contraction is one of the major reasons for loss of rope tension in case of outdoor installations. The temperature affects the size of the steel rope – it grows during the warm season and shrinks during the cold one. If the rope was tensioned during the cold season, then during summer, it will be loose. Taking this fact into account when establishing initial tension is recommended, especially in case of longer installations.

Anchor points are subject to movement due to several factors, including soil shifting and loosening of the fixations. Any tiny shift on each end results in sagging of the rope in the middle of the run.

Wear and fatigue of the old rope installation results in it becoming unable to keep the required tension. It might have broken wires or other deformations that prevent proper adjustment of the tension regardless of the settings of the fittings.

Practical Solutions for Maintaining Tension

Depending on the installation, different approaches should be taken, although certain principles can be applied universally.

Allow for the adjustment in your installation from the start. Fixed terminals leave no room for compensation for the stretch and movement that happen automatically. Installations with adjustable fittings (rigging screws and turnbuckles) provide possibility for re-tensioning without having to take apart the installation. This is a usual procedure for marine rigging, but also works fine for architectural installations, agricultural fencing, and industrial applications.

Adjust the initial tension above the necessary level. The initial stretch results in the rope being adjusted closer to the proper tension rather than becoming loose. The exact amount of the tension depends on cable construction, length of the installation, and load conditions.

Re-tension the rope after the initial weeks. Re-tensioning the rope within a month of installation eliminates most of the sag issues arising shortly after installation due to natural elongation.

Inspect the rope and adjust the tension seasonally for outdoor installations. Spring and autumn checks of tension account for the changes in tension due to thermal movement. When the right fittings are installed, adjustment is done within minutes.

Choosing the Right Tensioning Hardware

The choice of the fittings determines how easy maintenance of the rope tension will be.

Rigging screws with eye or jaw ends suit permanent architectural and structural applications. Closed barrel design of the screw protects the mechanism from moisture – important feature for installations that are subject to long-term weather exposure.

Open body turnbuckles provide same functionality but at the lower price point and are suitable for applications where the aesthetics are not as important – agricultural fencing, industrial support ropes, temporary structures and the likes. Open body makes it easier to monitor remaining thread engagement while adjusting.

For installations requiring precise tension control over longer distance or applications where the precise tension is critically important, using tension gauges is recommended at the initial phase of installation. Such simple devices eliminate any guesswork about rope tension and provide a base for future adjustment.

Regardless of the fittings used, it is important to ensure they are suited to the size of the cable and the expected load. Under-specification of the hardware causes the problems itself – the fitting deformed by tension becomes useless.

The Broader Context

Wire rope sagging is a maintenance issue, not an engineering inevitability. With the right fittings in place and regular seasonal check procedure, most installations will maintain their tension for years.

When dealing with existing installations that have problems with maintaining tension, it is worthwhile checking if anchor points are secure, the rope is still in a good shape and adjustment fittings were installed initially. Sometimes, adding a simple rigging screw to the installation helps greatly with maintenance of the rope tension in the long run.

For all types of tensioning hardware, wire rope, and other materials necessary for installation maintenance, browse our range of products.