This study investigates the influence of construction-joint geometry within the shear span on cracking, stiffness, deformation, energy absorption, and ultimate capacity of reinforced-concrete T-beams. Four beams were compared under three-point loading over a 1,000 mm net span (shear span, a = 500 mm; a/d = 2.94): a monolithic reference beam and beams containing vertical, inclined, and keyed construction joints in the shear span. All beams had identical reinforcement and a measured concrete cube compressive strength of 30 MPa. Relative to the monolithic reference beam, the jointed beams exhibited first-crack-load reductions ranging from 0.0% to 15.4% and ultimate-load reductions ranging from 0.9% to 4.5%. The maximum reductions in first-crack load and ultimate load were 15.4% and 4.5%, respectively, indicating that joint geometry affected cracking resistance more strongly than ultimate resistance. At 50 kN, the vertical, inclined, and keyed jointed beams exhibited midspan deflections that were 20.0%, 8.0%, and 3.0% greater than that of the reference beam, respectively. The keyed joint retained 97.1% of the reference secant stiffness at 50 kN and 99.1% of the reference ultimate load. Overall, the keyed configuration most closely reproduced monolithic behavior, plausibly because its geometry increased the effective contact area and mechanical interlock, whereas the vertical joint produced the largest stiffness and deformation penalty.
