Abstract
Composite frame beams utilize the composite action between steel beams and concrete slabs to improve bearing capacity and stiffness. However, the longitudinal slab reinforcement is generally interrupted by the steel column, limiting the slab contribution at the beam end under negative bending. Consequently, composite beams are often conservatively designed as bare steel beams, which may underestimate actual capacity and increase the risk of a strong-beam-weak-column mechanism. Existing solutions provide continuous force transfer by welding the slab reinforcement directly to the steel column. However, this detail may reduce the local stability and strength of the column flange and complicate on-site construction. To address these issues, this study proposes an integral composite frame beam with end-plate connections (ICFB-EP), in which the reinforcement is anchored to end plates bolted to the steel column. A finite element modelling approach validated against published experiments was used to investigate the monotonic response under positive and negative bending. Parametric analyses examined the effects of reinforcement diameter, concrete strength, column flange width, and steel beam dimensions. The ICFB-EP exhibited greater ultimate moment resistance and initial rotational stiffness than the corresponding bare steel beams, with approximately 25% higher ultimate moment resistance under negative bending in the comparisons examined. Reinforcement anchorage provided greater benefits under negative than positive bending. Failure was governed by tensile fracture and local compressive buckling of the lower beam flange under positive and negative bending, respectively. The existing calculation method overestimated the effective slab width at the beam end under positive bending; a revised expression was therefore proposed based on the numerical results to support the design of the ICFB-EP.