This paper presents a simplified beam design method for semi-rigid composite frames with vertical loading at the serviceability limit state. Equations were developed to determine the deflections of the com-posite beam allowing for both joint flexibility and beam sectional properties, along with a formula for the connection secant stiffness. The equations for the connection stiffness are more accurate than previous equations used because it considers the beam-to-column stiffness ratio and the beam-to-connection stiffness ratio. The equations were validated by the experimental results for two semi-rigid composite frames. The equations agree well with the experimental data because they take into account the actual beam-to-column connections and the composite action between the steel beam and the concrete slab. This paper presents a simplified beam design method for semi-rigid composite frames with vertical loading at the serviceability limit state. Equations were developed to determine the deflections of the com-posite beam allow for both joint flexibility and beam sectional properties, along with a formula for the connection secant stiffness. The equations for the connection stiffness are more accurate than previous equations used because it considers the beam-to-column stiffness ratio and the beam-to-connection stiffness ratio. The equations were validated by the experimental results for two The equations agree well with the experimental data because they take into account the actual beam-to-column connections and the composite action between the steel beam and the concrete slab.