Improving the Reliability of Measuring Critical Buckling Load in Sway Mode Frames

In the present study a method for improving the reliability of measuring the elastic critical buckling load of sway frames is proposed. The critical load is obtained by extrapolating the dependence between the lateral stiffness and vertical load that acts on the frame up to zero value of the lateral stiffness. The reliability is improved by planning of testing procedure and nearing the testing load to the buckling one. The testing procedure includes planning and correction of the lateral load during the experiments in order to avoid plastic deformations under high vertical loads. Theoretical dependence of lateral stiffness on the vertical load is obtained considering the stiffness in connections between the frame elements is found. Errors due to extrapolation, limited measurements’ quantity and measuring accuracy are considered. The theoretical results are further verified experimentally for various elements connection schemes. It is shown that using linear extrapolation of the dependence between lateral stiffness and vertical load provides high accuracy. Moreover, it’s determined that increasing the maximum testing load decreases the difference between the experimental and analytical values of the buckling load. Therefore the proposed method can be successfully used for testing sway frames in laboratory and real conditions.