Hi, I have a problem with the experimental buckling load that I have deduced for a compressive axial load applied to a tube of circular cross section. The buckling load is 2.34% larger than the theoretical buckling load! The beam is connected to supports via knife edges; these are rigid bodies and so will increase the overall buckling load of the beam. However using the correction factor deduced by Karman and Biot (1940) for this beam the buckling load is 1.000005 x P(theoretical), so the effect of hte knife edges can be considered to be negligible. What else might have caused this error? Position of strain gauges? Data acquistion program? thanks for any help.