Experimental and finite element analysis of permanent formwork impacts on flexural failures of reinforced concrete beams

The use of precast permanent formwork in construction is an advanced method gaining attention due to its numerous benefits, especially in projects where dismantling formwork after concrete pouring is challenging. While most previous studies focus primarily on the mechanisms of reinforced concrete (RC) components with permanent formwork under specific design scenarios, where the formwork design parameters remain largely unchanged, this study provides a more comprehensive understanding of how formwork affects the flexural failure mechanisms of RC beams. It aims to optimize formwork system design by considering a wider range of design scenarios. This study includes entirely original flexural tests and efforts to develop a finite element model with accurate component models, particularly applying a cohesive model for the interface between the formwork and the cast-in-place concrete. The key contribution of the study is its clarification of the flexural failure mechanisms of beams using precast permanent formwork systems through both experimental and simulation approaches. Additionally, it includes a comprehensive parametric analysis that identifies how permanent formwork can delay critical failure points, such as flexural cracking and reinforcement yielding, while enhancing the ultimate load-bearing capacity of beams. Notably, increasing concrete strength and formwork thickness is more effective in delaying the onset of flexural cracks, whereas augmenting the diameter or tensile strength of the reinforcement within the formwork is more effective in postponing the reinforcement yielding and enhancing the beam ultimate load. These insights offer new perspectives on optimizing formwork systems for improved structural performance.