Dynamic method for measuring critical buckling load of sway frames

The critical sway buckling load is the upper limit of the allowed vertical frame loading. This load is defined by the frame configuration, cross-sections of the columns and horizontal beams as well as configuration and stiffness of the connections between them. In known non-destructive methods of determining the side-sway frames critical load an implementation of vertical loading is technically difficult that is especially essential at full-size tests. The value of the applied load is limited also by significant deformation of the frame approaches the critical load value. The paper deals with a new non-destructive method for experimental determining the critical sway buckling load of frames. For ensuring mobility of the frame in the sway mode the vertical loading is carried out by the flexible traction element mounted between the frame beam and fixed base through the loading device. The critical vertical load of the "frame-traction element" combined system is higher than of single frame. This fact allows to load the system with loading that corresponds to critical load of a frame without loss of system stability. Procedure of the experiment includes: determining of free vibration natural frequency of the combined system "frame-traction element" for different tensions of traction element, determining the lateral stiffness of the system, calculation the corresponding stiffness of the frame and its critical load. The accuracy of the method is verified by comparison the experimental and theoretical results.