Bridge Residual Stress Testing

Bridge residual stress testing is used to measure stresses that are ‘locked-in’. Applications include measurement of stress in pre-tensioned or post tensioned structures and in-situ dead load stress in bridges.

Having an accurate understanding of the dead load stress is so important for understanding the health and capacity of a structure. We’re proud to have extensive experience with a huge range of services that can help determine dead loads and in-situ stresses in pipelines, bridges and other structures and special components.

Our in-situ stress determination techniques typically involve a controlled localised removal of material to measure the surface strain change, then relating this back to the usual stresses by measuring the material properties. In some situations, vibration measurement methods are used.

We have enhanced and adapted centre-hole drilling techniques to measure residual stress – this is mainly used in aerospace and mechanical engineering (as per ASTM E837-08) – for use in civil engineering applications. We worked with universities and client organisations to develop and calibrate data to make sure raw data is converted into accurate and insightful outputs.

Bridges and Structures

Frequently, the assessed structural capacity isn’t enough to support the live load that’s intended, and the effects of self-weight and dead loading have only been estimated. Likewise, there are situations where the physical condition and degradation of a structure can affect its integrity and capacity.

We provide multiple testing methods that are tailored for the material and characteristics of the specified structural element.

Concrete and Post-tensioned Structures

Because of the sturdiness risks that are associated with post-tensioned concrete bridges and the huge reliance on the strength of the tensioned tendons to support their load capacity, it is necessary to be aware of the local pre-stressing forces and their influence on global concrete stress.

The tests appropriate for concrete structures are:

• Concrete stress measurement using 78mm, 36mm or slot cutting
• Post-tensioning tendon load measurement on individual wires or solid bars

GET IN TOUCH

Masonry Structures

By measuring the pressure compensation slotting for load measurement between brick courses, you can find out the compressive stresses in masonry structures like retaining walls, bridges and tunnels.

Steel Structures

When investigating surface stresses caused by the manufacturing process, the centre-hole strain relief drilling method can be effectively applied.

The effects of dead loading and deduction of the localised effect of manufacturing processes can be measured by modifying this technique. By using careful planning to optimise the test, you can measure stress through the thickness of the material.

Cable Supported Structures

The average approach when measuring stay cables of hanger loads involves measuring vibration and calculating tension by using empirical equations.

The baseline level of dead load stress can be decided with each of these techniques. This can then inform the assessment calculation and can gauge structural health monitoring systems, so that changes to strain and load values can be measured.

Pipelines

Landslips and mining-related incidents put welded steel pipelines at higher risk of fracture due to ground movements.

Typically, three centre-hole drilling tests are completed at each cross-section – at 120-degree intervals around the circumference. Then, data is calculated from the stress and bending in the pipe. This information can then be used to determine whether the pipe needs to be fully excavated and jacked to relieve the bending. Strain gauges are usually fitted adjacent to the test locations while they’re exposed for testing so that future stress changes can be monitored.

Other Applications

We can apply these techniques to any and all scenarios and other residual stress measurements. Examples of this have included railway tracks, offshore structural nodes, helicopter rotors, nuclear power station elements, gun barrels, and train wheel sets and other components.