Keywords: aluminium, stress reduction, lifting brackets, finite elements, structural aluminium.

To increase the efficiency of fabrication, reduce welding and reduce costs a fabricator wished to determine if changing from their existing L shaped lifting bracket, fillet welded on four sides to the structural member, to a T shaped or block shaped lifting bracket fillet welded to the structural member on either four sides or on two opposite parallel sides would reduce aluminium stresses.

A 1000 N load was applied at the centre point on the horizontal top surface of the vertical upstand of the lifting brackets. The loads were applied individually in the positive x, negative x, positive y, negative y, positive z, negative z directions plus a twisting load to model the rotation of the structural member when being lifted.

Each model was analysed to determine the maximum principal nodal stresses in the welds, the lifting brackets and the base plate. Based on these results, the shape of the lifting bracket and the required number and location of the welds that gave the lowest principal nodal stresses was determined.

The base plate, welds and lifting brackets were modelled and analysed using linear elastic analysis and finite element software. Twenty node solid finite elements with three directional degrees of freedom, x, y and z per node were used together with finite elements which modelled the separation between the base plate and the base of the lifting brackets across the coincident nodes to allow sliding.

The results showed that the lowest maximum principal nodal stress occurs when using the T lifting bracket in 33 of the 38 cases considered, with the lifting brackets welded on four sides giving the lowest maximum principal nodal stress in 16 of the 18 cases considered. The T lifting bracket, welded on four sides was the preferred option

The maximum principal nodal stresses were compared with corresponding principal centroidal stresses. It was found, for example, for one case considered, the nodal stress results were between 32% and 257% higher than the corresponding centroidal stress results. Further investigation of the maximum principal nodal stresses showed they very often occurred at common nodes at the weld- lifting bracket interface or at common nodes at the weld-base plate interface. This led the authors to reduce their confidence in using maximum principal nodal stresses preferring to use maximum principal centroidal stresses for the assessment of these brackets.

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