Non-prismatic RC beams for ventilation integration in underground parking garages: experimental and numerical analysis and implementation

A major challenge in underground parking garage design is integrating structural systems with mechanical, electrical, and plumbing (MEP) services, particularly large ventilation ducts that often conflict with conventional beam depths. This study proposes a ventilation-integrated non-prismatic RC beam (VNP beam) with an inward-recessed mid-span section that accommodates ducts while maintaining structural capacity. A combined program of nonlinear finite element analysis and full-scale testing was conducted on VNPB850 × 600 beams to evaluate flexural behaviour, load capacity, and deformation performance. The VNP beam achieved an ultimate flexural capacity of approximately 1579 kN and exhibited a more uniform stress distribution and enhanced plastic energy dissipation. The recessed geometry effectively guided stress flow, reduced stress concentrations, delayed reinforcement yielding and crack initiation, and improved ductility and post-peak stability. A deep-learning-based semantic segmentation method was subsequently used to automatically extract and map crack patterns that closely aligned with high-stress regions. Quantitative analysis identified 183 cracks with an average length of 136 mm and a width of 2.0 mm, mainly concentrated within the recessed web and shear zones. In practical applications, the VNP beam can reduce story height by 250–350 mm, resulting in considerable construction cost savings.