I have always been fascinated by the underground mine headgear, or headframe as it is called in North America. I love the idea of the hoist that lifts men and materials from deep below to surface.

Thus I was intrigued when Wardrop provided this brief Project Description entitled Structural Health Monitoring by Dr. Emile Shehata and Robert Van Ginkel.

With the need for increased production, the impact of higher hoisting speeds on the structure supporting the hoist was recently evaluated for the PCS Potash – Allan Division. This elevated steel structure is known as a headframe and is susceptible to vibrations that became more of an issue at higher hoisting speeds. In order to assess the impact of these vibrations on the headframe, a thorough structural and mechanical investigation was undertaken. A numerical structural analysis for the headframe was undertaken by Wardrop engineers and PCS Allan personnel. The team is also taking innovative measures by conducting in-service structural health monitoring (SHM) to assess the headframe structure. The PCS Allan site was the first site to be assessed this year using the SHM techniques.

The technique involves the use of two sensors along with a mobile Data Acquisition system (DAQ) to monitor the headframe’s structural response to different motor speeds. A tilt-beam sensor to measure the vertical rotation (tilt) and a tri-axial accelerometer to measure the acceleration in the horizontal direction were used for the in-service structural monitoring. The two sensors were installed on a column located at an elevation just below the motor floor. Data recorded from the sensors indicated that the motor causes the structural deformation to increase by 30 percent while the motor speed increase is only 16 percent. This is attributed to the fact that the oscillation of the motor is getting close to the fundamental natural frequency of the structure. With this information, measures to improve the dynamic characteristics of the structure can be looked at to allow for even higher motor speeds.

To put it simply, using the SHM techniques, Wardrop engineers are checking how many beats per minute the heart of the structure and the effect the higher heart rate has on the structure.