Reinforced concrete (RC) structures are subjected to combinations of axial, shear, flexure, and torsional loading during an earthquake event. Comprehensive understanding of the behavior of shear panels is essential to predict the response of members under combined loading. This work focuses on the analytical modeling of RC shear panel elements. A baseline fixed strut-angle model (FSAM) was initially proposed for the shear behavior of RC panel elements, satisfying the three basic principles of mechanics: stress equilibrium, strain compatibility, and material constitutive behavior. The FSAM was later modified to consider the effect of dowel action and aggregate interlock through empirical relationships. Use of modified FSAM formulations for the estimation of the monotonic response of shear panels with different reinforcement ratios in longitudinal and transverse directions leads to loss of convergence after yielding of the transverse reinforcement. Thus, an accurate estimation of postyield response is not possible using the existing FSAM, which is critical for seismic design. This paper presents an improved algorithm for FSAM by employing experimentally validated constitutive relationships for the aggregate interlock mechanism. Comprehensive correlation studies considering parameters including the amount of reinforcement and concrete strength are reported to understand the improved FSAM. Predictions of the improved FSAM for shear panels with unequal reinforcement are better than those derived using the existing FSAM approach. © 2021 American Society of Civil Engineers.