IDAC Performs Structural Analysis on Shaft Lift Structure
Stannah Lifts required a lift shaft structure originally designed for hydraulic lifts 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, the applied load (imposed load from the lift car) is applied downwards at the top of the guides.
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 chassis. The stress distribution, deflected geometries and safety factors were reviewed to assess the structural performance of the structure.
Stannah Lifts provided IDAC with the geometry. This was then 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 chassis 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 model was meshed with high order solid elements and solidshell elements. 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 chassis lift at two different heights. The location of the chassis lift was parameterised so that any location could be analysed. Four loading locations were used to represent the chassis lift 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, 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. The regions that did have safety factors less than 1.5 were located at the top of the structure and a safety factor of 1.28 (135MPa – maximum stress) was seen at this location for both load cases.
The FE analysis of the traction lift structure showed stress levels below two thirds of the yield stress in all components including the welds. High stresses of 135MPa were found to occur locally and were deemed not to affect the integrity of the structure; however, there may be an impact in a fatigue assessment.
Use of the sub-modelling technique and inclusion of any non-linearities could assess the stress levels and distribution on these parts more accurately.
A finite element analysis of the lift structure provided an invaluable way of assessing design performance prior to installation.