The design and analysis of static pallet racking systems.
The essential purpose of a pallet racking system is to support the largest load possible in relation to its self weight, while maintaining ready access to individual pallets and preventing damage to stored goods. This should be achieved within the constraints imposed by design and safety considerations. This basic requirement has ensured that most current rack designs consist of thin-walled (<3mm) steel elements whose self weight typically accounts for between 2% to 3% of the total weight of the structure. In general, the design is complicated by the semi-rigid nature of beam/upright and upright/floor connections, and by the use of perforated upright members in large, multistorey sway frames.Currently, a UK code exists (SEMA) to design racking installations using a permissible stress philosophy. However, the development of limit state design in conjunction with advances in computing power and the emergence of the single European market have combined to create an environment in which the development of a new European design code has become logical and desireable. A code has been developed at the request of the European industrial pallet racking manufacturers association (FEM), to take account of the latest developments in steel design. When the FEM code has been fully evaluated (to April 2000), and assuming that no modifications are necessary, it will be implemented as a Euro-norm with the intention of replacing all of the national codes in Europe. This thesis is intended to form a part of that evaluation process. The purpose of this document is to examine the performance of a single manufacturers industrial pallet racking system in relation to the FEM code. In the first instance, this involved the design and application of suitable experimental procedures, followed by the completion of a sufficient number of tests to generate a reliable statistical characterisation of each of the components in the system. Approximately 2000 tests were completed during the course of this exercise. An approach was subsequently established using this characteristic test data, and based on the recommendations contained within the FEM, in order to predict the load capacity of any given racking system. To this end, the use of finite element predictive software was investigated, typically incorporating second order analysis techniques to the treatment of sway frames with loose and semirigid connections. This 'novel' design approach has been documented using a detailed worked example. Any considerations necessary for the purposes of design are included within a full design procedure.The European code has subsequently been compared to the national SEMA code, in order that an assessment can be made of the accuracy and limitations of each. This includes an investigation into the key differences between test methodologies and the interpretation of experimental results. In addition, twenty eight structures possessing a broad range of rack geometries have been analysed using each code, in order that conclusions can be drawn on the consequences for the UK racking industry of designing to a new European code. This investigation has calculated a mean reduction in load carrying capacity of 15.2% for FEM designed rack, with a range distributed between a 12.8% increase in capacity to a 36.5% reduction. This is the first indication available as to the effect of the implementation of the FEM code on the load capacity of racking. Finally, a sensitivity analysis has been performed on twenty four further structures to identify some of the critical factors that are most influential in determining the load carrying capacity of a rack, based on the design approach already identified. Variables included: beam end connector looseness; moment capacity and rotational stiffness; floor connector stiffness and upright yield stress.
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Sheffield Hallam University (United Kingdom).