IDAC Case Study - Structural Analysis of a Shaft Lift Structure


	Stannah Lifts Ltd Structural Analysis of a Shaft Lift Structure

Company Profile

Born in the 1860s, Stannah has its foundations in lift engineering. Always an innovative passenger lift manufacturer, Stannah expanded their portfolio of products in the 1970s to include their world-renowned stairlifts that give people invaluable freedom in their own homes. More recently escalators and moving walkways have been added to their product range.

Over the years they have developed an impressive level of expertise in moving people and goods quickly, safely and comfortably. Working with architects and other professionals to create leading edge designs, they build passenger lifts and goods & platform lifts that last the distance with the back up of great local service nationwide should it ever be needed. All this and more can be found at www.stannahlifts.co.uk

Background

Stannah Lifts Ltd required a lift shaft structure originally designed for hydraulic lift to be reused in a traction lift. As such a new set of forces and boundary conditions needed to be re-evaluated on the structure. With the traction drive, a component of the applied load acts downwards at the top of the guides; no such load exists on a hydraulic lift.

IDAC were required to investigate the structural response of the assembly subjected to these new loading conditions. The Traction Lift structure was analysed for two positions of the lift and were chosen since they were perceived to impart maximum stresses to the structure. The stress distribution, deflected geometries and safety factors were reviewed to assess the structural performance of the structure.

Analysis

Stannah Lifts Ltd provided IDAC with the geometry files in Autodesk Inventor format. This geometry was simplified to remove all non-structural parts and small features that would not affect the stiffness of the system, but would reduce the size of model and hence save time. The lift car and the counterweight were not explicitly modelled; however non-structural parts were added to the model to identify the locations where the loads needed to be applied. The entire model was meshed with high order solid elements and SOLIDSHELL190. The mesh was refined in the areas where the stress gradients were high. ANSYS contact elements were used to ensure connectivity throughout the model. All materials were assumed to behave elastically and homogeneously for the purpose of the design evaluation.

Two load cases were analysed representing the lift car at two different heights. The location of the lift car was parameterised so that any location could be analysed. Four loading positions were used to represent the lift car location, two for the pull out forces and two for the push in forces (horizontal forces). In addition to the horizontal forces, vertical forces were applied at the top of the main and counterweight guides. The same set of constraints was applied for both load cases.

Under the two loading environments analysed, representing expected ‘worst case’ conditions, almost all of the regions of the traction lift structure had a safety factor greater than 1.5 based on the yield stress of the material. Regions with safety factors below 1.5 were examined in greater detail & it was concluded that the structure would not fail for the loading conditions assessed.

The graphics below show some of the equivalent stress plots for loadcase 1.

Detail showing mesh of some component parts of the lift structure.

	Design Benefit Finite element analysis of the lift structure provides an invaluable way of assessing design performance prior to installation.