Reinforced concrete precast beam with a stepped joint

The object of research is a precast reinforced concrete beam with a stepped joint strengthened by composite reinforcement bars. Method. The study employed an experimental-numerical approach. Four beam specimens were prepared, including one monolithic control specimen and three composite specimens consisting of two reinforced concrete parts connected by a stepped joint. The joint zone was reinforced with composite rods installed in preformed holes and grooves. Static loading tests were carried out using a P-50 hydraulic press to determine the load-bearing capacity, deformation response, and failure pattern of the beams. In parallel, a finite element model was developed in the LIRA-SAPR software package with consideration of the physical nonlinearity of concrete. The numerical model was calibrated and compared with the experimental results. Results. The experimental study showed that the reinforced concrete precast beam retained its load-bearing capacity up to an ultimate load of approximately 25 kN. Failure occurred predominantly in the stepped joint zone and was accompanied by crack development, local concrete damage, and loss of stiffness. Numerical analysis reproduced the general deformation pattern and stress concentration in the joint region; however, the calculated ultimate load exceeded the experimental one by approximately 1.8 times. The discrepancy is attributed to material heterogeneity, technological imperfections in specimen fabrication, and the simplified representation of the joint behavior in the numerical model. The results confirm the feasibility of using stepped composite joints in precast reinforced concrete beams, while indicating the need for further optimization of anchorage depth and reinforcement layout to improve structural performance.