Padeye strength

Padeyes are frequently applied for use as lift points or as hinged connections.Several calculation methods are available (from class and industry) for strength assessment of padeyes. Generally, the following stresses are evaluated:
  • contact stress between pin and eye
  • tensile stress next to the eye
  • tensile stress at the “extreme fibre” of the eye plate
  • shear stress in the eye plate.

Stresses in the connection of the padeye to the structure and in the welds of possible doubler plates in way of the eye are important as well, but not subject of the current project.

Not all methods make use of all stresses mentioned, reflecting different philosophies on stress components governing padeye design. Formulae for stress calculation show principal differences between methods. All methods are using more or less approximate (nominal) calculation methods. However, the compact geometry of padeyes will cause actual stress peaks deviating from the nominal values. These stress concentration effects are accounted for by factors on loads or nominal stresses and / or relatively low allowable stresses. Each method has its own set of factors. Obviously all existing padeye methods are based on experience and give no insight in the actual stress peak values. Furthermore, it is not clear which stress components are actually critical for strength.
ver variables padeyeVER stress 1 padeyeVER stress 2 padeyeVER padeye
Eye plate variables

Tensile stress next to eye
Contact stress padeye

Padeye on platform

R&D project
Eye plate structures are designed for ever growing load levels. In order to guarantee structural safety as well as economic design (plate thickness) Vuyk Engineering Rotterdam initiated a research and development project with the goal to clarify above issues and to develop a tool for more accurate padeye strength analysis.

Finite element analysis is applied to investigate the stress fields in padeyes for a range of geometries and load directions. It was found that each padeye generally is governed by the peak tensile stress at the edge of the hole only. Extreme fibre tensile stress is secondary and shear stress is not significant.

As a next step, the contact condition between the pin and the eye plate was considered. It was found that the classic Hertz theory is very well suited for the contact pressure analysis. The influence of the clearance between the pin and the eye as well as the relative magnitude of loading on stress peaks was investigated. It appeared that higher load intensities have a favourable effect on stress concentration effects, depending on the clearance applied. This resembles the supporting effect of the pin on the padeye where a larger padeye deformation (related to larger stresses) induces a larger contact area which on its turn lowers the stress concentration.

All analyses are performed using fine-mesh models including the modelling of the contact zone which requires non-linear calculations. Using these FE routines for each padeye design is not practical. Therefore, FE results were systematically generated and used as input for a spread sheet program. This tool now facilitates the quick and accurate evaluation of padeye strength, based on thorough knowledge of eye plate stress response and the pin to eye interaction behaviour.

Future developments
Strength evaluation requires accurate stress analysis on the one hand in combination with knowledge of allowable values on the other hand. Allowable stresses should be based on structural failure modes with corresponding critical (failure) values. Since the failure limit of padeyes is not as obvious as one might think, another research project is currently ongoing at Vuyk Engineering Rotterdam.