Local Fracture of a Reinforced Concrete Beam Under High-Velocity Impact on Biaxial Bending and Torsion Deformation

Designing buildings and structures that meet advanced mechanical safety standards is a relevant task in the present-day socio-economic environment, given that structural safety is evaluated by resistance to progressive collapse. The design of key elements, capable of withstanding accidental actions, means preventing the escalation of progressive collapse. This task also involves evaluating the bearing capacity of reinforced concrete beams under high-velocity impacts triggering supplementary dynamic loading by bending and torsion moments. The authors present their method for the dynamic load analysis based on the development of limiting surfaces. For this purpose, the value of the J-integral is computed to analyze the fracture of a rebar, and the inability of a rebar to take loads is simulated by a normalized time function. The resulting conclusion is that the proposed design method, applied to key elements of buildings and structures, improves their mechanical safety in the case of dynamic loading that causes local damage and triggers resistance to combined stress, including bending in two planes and torsion. It has been established that at a bending load level constituting 80% of its ultimate value or higher, a combined impact bending-torsional load, as low as 25% of its own ultimate capacity, can cause the rupture of tensile reinforcement and lead to a loss of mechanical safety in conventionally designed beams.