The global plastic pollution crisis is a pressing issue that demands urgent and innovative solutions. In recent years, the integration of 3D printing technology in the construction sector, particularly in large-scale projects using recycled plastics has shown promise. However, a significant gap remains in understanding the structural behavior of such materials during the design process. This is further complicated by many architects’ limited familiarity with 3D printing technology, which hinders its broader adoption in architectural design. This paper presents a study focused on simulating and evaluating the structural behavior of 3D-printed stairs mounted on a steel framework. Using finite element analysis (FEA), the performance of stairs fabricated from recycled plastic is investigated. The methodology involves designing stair elements in the Grasshopper environment, setting up the FEA model, and conducting simulations in Abaqus. Key steps include defining material properties and cross-sections, generating the mesh, applying boundary conditions based on the European Organization for Technical Approvals (ETAG 008), and running the analysis. The results of the FEA will guide iterative adjustments to the printing setup, aiming to optimize the final design. This study aims to demonstrate how architects can effectively use FEA tools to evaluate their designs, particularly through examining stress distribution and spatial displacement. The findings offer valuable insights into the mechanical response of large-scale 3D-printed plastic components, highlighting their potential for diverse applications in sustainable construction.