Deformation of crane hardstands

Abstract

Crane hardstands serve as crucial platforms for supporting heavy lifting equipment and ensuring operational efficiency. However, crane hardstands are not infinitely stiff and will deform upon loading. Uneven loading during wind turbine installation will result in differential deformation of the crane hardstand, causing the crane to tilt. A small tilt of 0.3°, which is equivalent to around 30-60mm differential settlement depending on the crane, will create safety hazards, causing construction to be discontinued. As a result accurate deformation predictions are required to design a sufficient crane hardstand.

This research is conducted to investigate the influence factors of the deformation of a crane hardstand, evaluate the current prediction method and to improve the accuracy of future deformation predictions, so the hardstands can be designed more efficiently.

The research begins with a literature study on the above surface influences on the magnitude of the load and the corresponding soil behaviour of the soil profile beneath the hardstand. Furthermore the current prediction method is analyzed to dictate shortcomings. The expected influences found in the literature study are examined with full scale monitoring and testing cases. Finally, a sensitivity analysis is performed on the current prediction model to specify the parameters with the biggest influence on deformation for different variants. These parameters are then assessed on how a more accurate determination might influence the predicted deformations.

The numerical simulations are carried out using advanced finite element analysis software Plaxis, specifically the HS(small strain) model. This model enables the investigation of various factors affecting hardstand deformation, such as varying soil stiffness, load distribution, and foundation characteristics.

The biggest shortcoming of the current prediction method is found to be the exclusion of time dependent behavior. And the most influential soil parameters of the HS(small strain) model after the addition of a consolidation phase to the model are found to be the stiffness and permeability parameters. The deformation prediction is done for the entire range of uncertainty of these parameters (5-, 25-, 50-, 75-, 95- percentiles) to quantify prediction accuracy improvements were these parameters determined witch precise. For both peat and clean clay the permeability coefficient is found to, when determined more accurately, have a 50% chance to result in a predicted deformation reduction of between 40 to 60 %, while a more accurate prediction of the stiffness parameters E_oed E₅₀ E_ur has a 50% chance to result in a predicted deformation reduction of between 65 to 75%

The findings of the research can be used by engineers to test the effectiveness of their own hardstand deformation prediction method and provide advise on the benefits extra soil investigation might lead to.



Keywords: Crane hardstands, deformation analysis, differential settlement, cyclic loading, Hardening soil small strain, FEM-modeling, sensitivity analyses.