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This article presents a comprehensive, step-by-step tutorial on modeling a reinforced concrete beam using OpenSeesPy. Focusing on a simply supported beam with a 600‑inch span and a 24‑inch depth, the tutorial covers everything from establishing a basic two-dimensional model and defining nodes and support conditions to assigning nonlinear material properties for both concrete and reinforcing steel. Special emphasis is placed on constructing a detailed fiber section model—which discretizes the beam's cross-section into concrete patches and steel layers—to capture the nonlinear moment–curvature behavior accurately. Finally, the guide explains how to apply loads, run a static analysis using a force-based beam–column element, and post-process the results by extracting the mid-span displacement. Whether you're a practicing engineer or a student in structural analysis, this tutorial provides a clear pathway to using OpenSeesPy for advanced reinforced concrete modeling from openseespy....