Load-carrying ability of traditional and pre-stresed bimetallic beams under plastic response of their wall material

The article theoretically determines maximum load-carrying ability of traditional bimetallic beams, optimal distribution of material along flange sheets and wall, and height of wall material zone of flowage. It is established that using high-strength steels according to GOST 27720 for bimetallic beam flanges, plastic deformations of wall material penetrate into depth of beam section at the distance of 0.3h (h-height of beam section). There is no plasticity hinge in wall material. The problem of finding depth, length and areas of plastic deformations in bimetallic beams prestressed by wall stretching is solved. Based on the works of N. A. Makhutov and R. Peterson, stress concentration coefficient and safety factor of pre-stressed beams are determined. Service life of beams with zone of plastic deformation in wall is 1.338. When a beam is cyclically loaded, its prestresses reduce the level of stresses causing plastic deformation and at the 9thor10th loading cycle, fluidity of wall material is eliminated. The study establishes the law of monotonic decrease in the height of plastic deformation zone of beam wall material. Reduced modulus of elasticity of the material of prestressed beam in state of elastic-plastic deformation is determined. It is established that margin of relative plastic deformation is 1.738. Based on the fourth energy theory of Huber, Mises and Gencki, limiting reduced stresses are determined, indicating absence of brittle cracks probability in plastic deformation zone of wall material. The local yield limit of material and its stiffness coefficient are established.