Numerical Study on Semi-Rigid Racking Frames

摘要

Slender beam and column structures are used in the storage industries for palletised goods. All connections between uprights and beams, at upright splices, and between uprights and base-plates, are usually semi-rigid. Experimental momentrotation curves for these joints are highly non-linear. This paper is concerned with the analysis of a pinned-base portal frame under a combination of point loads normal to the ground and with proportionally increasing side loads. Stability functions were used to model the beam and the uprights. Semi-rigid joints at the end of the beam were incorporated into the beam stiffness matrices. rnUsing a mirror arrangement of portal frames tied together by a tension jack an experimental investigation was undertaken. Single storey portal frames were tested with different percentages of side load and were free to sway. To investigate joint behaviour numerically three different models were used in the analysis. The most accurate model was a multi-linear model consisting of a tri-linear loading curve together with a bi-linear unloading curve. The second and third models used bilinear loading and unloading lines with the same slopes used for loading and unloading. The values of the elastic stiffnesses were chosen to be the stiffness at half the ultimate failure moment (as used in the SEMA code) and the value of stiffness as calculated by the FEM code. The multi-linear loading model agreed closely with the experimental results for both moments and the deflection. The FEM model gave moment results with gave the same accuracy as the tri-linear analysis but gave sway deflections which were typically 10% higher than the experimental values. The SEMA code stiffness is higher than the values used in the other analyses and produced deflections which were significantly lower than experiment. rnThe multi-linear model was applied to analyse two storey, single bay and two bay, single storey frames.