This study investigates the flexural behavior of hybrid reinforced concrete beams incorporating both steel and glass fiber reinforced polymer (GFRP) bars. A combined theoretical and experimental approach was employed. The theoretical analysis developed analytical models to predict flexural response at various loading stages, considering different failure modes (concrete crushing, steel yielding, and GFRP rupture). The experimental program tested four singly reinforced concrete beams (steel-only, GFRP-only, and two hybrid combinations) under three-point bending. Results showed that hybrid beams develop a gradual yield point between cracking and ultimate loads, unlike GFRP-only beams, which fail immediately after cracking. This observation is consistent with theoretical predictions. The theoretical analysis also indicated increased ductility, measured by the deflection ratio at ultimate to yielding, with increasing GFRP ratio (1.06, 3.68, and 8.34 for 0%, 33.33%, and 66.67% GFRP area content, respectively), suggesting a corresponding decrease in stiffness. Experimentally, increasing the GFRP ratio reduced the ultimate load-carrying capacity, with 114.29 kN, 102.24 kN, 80.05 kN, and 61.71 kN for 0%, 33.33%, 66.67%, and 100% GFRP, respectively. The failure mode observations revealed GFRP debonding, particularly in the GFRP-only beam, which prevented it from reaching its expected capacity. All beams exhibited flexural-shear cracking, affecting load capacity. Beams with a higher steel-to-GFRP ratio showed a more distinct yield point, while those with a higher GFRP-to-steel ratio tended to maintain higher load capacity until debonding. This research provides insights into the behavior of hybrid reinforced concrete beams and proposes a procedure to calculate the ultimate moment capacity of the beams.
Phattaraphong Ponsorn (Mon,) studied this question.