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PROCEEDINGS OF THE ELEVENTH INTERNATIONAL CONFERENCE ON COMPUTATIONAL STRUCTURES TECHNOLOGY
Edited by: B.H.V. Topping
The Effects of Seismic Loading on Pallet Rack Semi-Rigid Joints
K.O. Kwarteng1, R.G. Beale2, M.H.R. Godley2 and S.D. Thomson1
1CS&A Capability, Risley, United Kingdom
K.O. Kwarteng, R.G. Beale, M.H.R. Godley, S.D. Thomson, "The Effects of Seismic Loading on Pallet Rack Semi-Rigid Joints", in B.H.V. Topping, (Editor), "Proceedings of the Eleventh International Conference on Computational Structures Technology", Civil-Comp Press, Stirlingshire, UK, Paper 21, 2012. doi:10.4203/ccp.99.21
Keywords: seismic, pallet racks, semi-rigid joints, steel structures, numerical modelling.
A literature review  of existing research on rack structures shows that connection models that are often adopted for the study of frame behaviour are usually based on the pre-yield stiffness of these connections.
This paper shows an alternative means of investigating the semi-rigid and post yielding behaviour of a typical beam-end connector. Under seismic loading pallet rack connections undergo degradation of stiffness called the pinching effect. The pinching behaviour of the connection was determined through experiments. The pinching was associated with a significant looseness in the connection and this was shown in the moment rotation curve to get bigger with increases in the number of load cycles. A connection model to describe the "butterfly shaped" stiffness curve was then developed through regression analysis and is given in the paper.
Numerical models of sample pallet rack frames were then investigated using Ansys. and subjected to simulated earthquake loadings Comparisons of the behaviour of the frames were made with different connection models - firstly using rigid joints, secondly using the European racking code BS EN15512 , thirdly, stiffnesses calculated using the European scaffolding code BS EN 12812-3  and lastly, using the stiffnesses found by the experiments. From these studies the experimental stiffness was found to be more ductile than the bi-linear stiffness of the European finite element code  however, with the introduction of either a single coefficient to account for pinching or a slight reduction in the recommended Eurocode load factors the bi-linear stiffness derived using the Eurocode for scaffolding code  was found to give results that were generally within 5% of those produced using the experimental moment - curvature curve. It was then concluded that although the moment - curvature curves from the experimental specimens exhibited low stiffnesses due to the pinching effect, these stiffnesses did not affect the overall structural behaviour under simulated earthquake as the rotations required for pinching to occur were not achieved for the earthquake simulations.
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