Case Study: Using Motion Amplification Techniques to Investigate and Resolve Structural Cracking Issues

Our Asset Excellence Team is comprised of Engineers with a passion for problem solving, asset health monitoring, investigating asset dynamics and resolving troublesome asset failure modes at their root cause.

In-house, real-time data acquisition tools include motion amplification, synchronous vibration data capture and of course access to Rockfield’s Design team who are specialists in simulating dynamic and modal scenarios involving both forced and/or natural excitation motives.

In this particular case, real-time data revealed that there was no loading/excitation bias being transmitted to the troublesome monorail. Despite this, the motion amplification study revealed two conclusive outcomes:

1. The dominant flexure mode in each monorail was a natural mode (which occurred at a slightly different for frequency for the troublesome monorail).
2. The physical flexure being generated by this natural mode was significantly higher at the troublesome monorail.

Whilst physically checking the integrity and structural bracing arrangements around the troublesome monorail, the structural bay supporting the troublesome monorail was found to contain unique structural brace connections.

Project overview:

Dynamic simulations were run for both structural bay types, confirming that the variation in brace design was the root cause of the additional monorail flexure. Peak stresses of 60MPa were predicted in the troublesome monorail (at the location of cracking), compared with 29MPa in the sister monorails. A BS7608 assessment then confirmed that the troublesome monorail was the only one likely to have a finite service life.

Rather than replacing the unique brace connections (a relatively significant undertaking), Rockfield simulated and produced fabrication drawings for a new bolt-in monorail installation that achieved an infinite fatigue life without having an adverse effect of the dynamic response of the local area or the broader structure.

This project consisted of the following tasks:

• Real-time data acquisition – to quantify the excitation levels transmitted to each monorail by overhead vibrating screens.
• Motion amplification – to capture and quantify the physical flexure (or dominant mode shape/s) apparent at each monorail.
• Dynamic simulation – to replicate the physical flexure of each monorail, quantify cyclic stresses and determine the dominance of natural and forced modal responses.
• Fatigue analysis – to determine whether cyclic stresses form a catalyst for cracking; and if so, where cracking would be most likely to occur.
• Remediation – to predict the dynamic response and root cause remediation effectiveness of Engineered solutions prior to installation.
• Support – to ensure the client has what they need to execute and measure the success of the solution (from fabrication drawings to a turn-key project management solution).