31 January 2022

        MRT of Bridge Cables

A recent project saw TENSOLOGY carry out condition assessment of large diameter, sheathed locked coil hanger cables on a major road bridge.  The assessment method included Magnetic Rope Testing (MRT) of the free length of cable in order to check for any signs of damage or deterioration.

The Jack Williams Gateway Bridge is a skewed bowstring arch bridge, spanning 70m across the A465 near Abergavenny in Wales.  The deck is connected to the arch using locked coil rope assemblies which are over-sheathed with white HDPE, providing additional corrosion protection and increasing the aesthetic appeal of the bridge.  A total of 20 sheathed locked coil rope assemblies, each with an outside diameter of 92mm, are incorporated in the structure. 

When the client wanted to check the integrity of the hanger ropes, they placed their trust in the knowledge and experience of TENSOLOGY.  The use of sheathed hangers presents an obvious problem in relation to the conventional means of condition assessment - it is not possible to carry out a visual inspection of the steel wires.   The fact that the bridge carries road traffic and sits approximately 30m above a busy trunk road also creates its own difficulties when it comes to inspection.

In order to check the integrity of the ropes, TENSOLOGY first carried out a site visit and then worked with the client to develop a safe and effective method, with all risks identified and mitigated.  INTROS Magnetic Rope Testing equipment was chosen to carry out the test due to its ability to “see through” the HDPE sheathing and check right through to the centre of the rope.  The INTROS equipment utilises strong rare earth magnets to fully magnetise the section of rope under test and a number of different internal sensors to accurately detect, locate and quantify any deterioration or damage to the underlying steel.  The locality of the inspection demanded that all work was carried out under night time road closures with the amount of time on site strictly limited.  In order to guarantee that testing was completed within the allowable timeframe, a novel method of moving the MRT equipment along the rope was employed.

With all plans in place, the A465 trunk road was closed, diversions set up and the testing was successfully completed.  Following testing, TENSOLOGY engineers established the condition of the hangers by analysing data using WINTROS software and a written condition assessment report was issued to the client.