Elastic buckling strength evaluation method of ribs used in support structures

Abstract

Ribs are used to increase the stiffness of support structures such as skirts and lugs. The ribs are usually welded on two sides to the skirt and base plate or to the vessel and lugs, and often free on the other two sides. The skirts and lugs, which are the support structures of the vessel, generate a large moment mainly due to the response to earthquakes, and the ribs provided on the skirts and lugs are subjected to compressive loads due to the moment. The rules on design and construction for nuclear power plants of the Japan Society of Mechanical Engineers have restrictions on the width-thickness ratio and the effective slenderness ratio in consideration of the buckling of members subjected to compressive loads. These are shape restrictions considering the buckling of the plate under compressive load, and do not correspond to the loading conditions and support conditions of the two-side fixed ribs under the moment mentioned above. In order to clarify the buckling behavior of the ribs, buckling eigenvalue analysis was performed to obtain the buckling moment and the elastic buckling modulus for the ribs constrained on two sides.