The steelwork was being modified to support a new vibratory screen, feed chute and discharge chute.
Dynamic loads on the vibratory screen were provided by excitors (motor-driven eccentric masses attached to the screen), which shook the screen to separate washed coal based on size. The coal screen was supported on coil spring suspension to isolate the structure from vibrations at the operating frequency.
Advitech was provided with the proposed structural steel layouts and equipment drawings and specifications. We used this information to:
- determine the loadings applied to the structure and review in combination with AS 1170 structural design actions
- assess the existing and proposed steel modifications in accordance with AS4100 steel structures.
Dynamic loads were assessed using Strand7 modelling software, while dynamic actions were calculated based on the excitor mass and the mechanical eccentricity provided in the excitor OEM drawings. The screen was modelled with spring connections to correctly simulate the transfer of dynamic forces to the structure. Structural response was determined for excitor frequencies from zero to twice the operating frequency.
The vibratory screen OEM recommended vertical vibratory modes should be avoided within a ±7Hz band of the screen operating frequency. In order to achieve this requirement, we recommended certain modifications be made to the proposed structural steel layout and members.