Measurement and assessment of geometric imperfections in thin-walled panels

Thin-walled members may be subject to performance limitations arising throu gh local or distortional buckling of slender elements comprising the cross- section of the member, or overall buckling of the member. The effects of st ructural instability may be aggravated by the presence of geometric imperfe ctions in these elements. An investigation is presented into methods of mea suring and assessing geometric imperfections in cold-rolled thin-walled ste el panels. These methods can be used to characterise the geometry of prisma tic thin-walled members that exhibit performance sensitivity due to geometr ic imperfections. The measurement procedures investigated include close-ran ge photogrammetry, precise optical levelling, and the use of a co-ordinate measurement machine. The assessment procedure comprises a least-squares spe ctral decomposition of the measurements to characterise the imperfections e xistent in the panels under investigation, and estimates of the precision o f the derived Fourier coefficients are used to inter-compare the three meas urement procedures. The investigation has demonstrated that statistically s ignificant imperfections may exist in thin-walled members at short and medi um wavelengths, leading to a reduction in the load carrying capacity. Both optical levelling and the co-ordinate measurement machine technique can yie ld desirable results, but for high precision work, use of the co-ordinate m easurement machine is recommended. (C) 1999 Elsevier Science Ltd. All right s reserved.