Structural Behavior of Stiffened Knee Joints with Thin Webs

Ten experiments concerning the carrying behavior of square knee joints are performed. It is shown that, analogous to transversely stiffened girders with thin webs, tension fields that are anchored on flanges also develop in knee joints. The load capacity of the knee joint is limited by the formation of plastic hinges in the flanges. Comparison with the buckling load shows that a stiffened knee joint with a thin web plate exhibits considerable overcritical load reserves. The failure mechanism of stiffened, square knee joints is described using a simple tension field model. This model introduces two load-carrying parts: one part carried by a shear field, the other by a tension field. The calculated load capacities are approximately 10% greater than the experimentally determined capacities. Further tests are proposed to verify the model and to derive a design concept.