Experimental study on section optimization and flexural behavior of UHPC-NC composite beams

Purpose This study proposes a UHPC-NC composite beam system to address deformation incompatibility issues caused by significant elastic modulus mismatch in conventional steel-NC composite beams. To further reduce the construction cost of UHPC-NC composite beams, an optimal cross-section design method based on an improved genetic algorithm is introduced. Design/methodology/approach Taking a 16 m simply supported T-beam as the engineering case study, a preliminary UHPC-NC composite beam cross-section is designed. With material cost minimization as the objective function and cross-sectional parameters as variables, an optimization model incorporating bearing capacity and deformation constraints is established. An enhanced adaptive genetic algorithm is employed, wherein crossover and mutation probabilities are dynamically adjusted to substantially improve global optimization performance and convergence efficiency. The mechanical performance and practical behavior of the optimized composite beam are validated through a 1:2 scaled four-point bending test. Findings The optimized UHPC-NC composite beam achieves a 21.91% reduction in total life-cycle cost, significantly improving economic feasibility. Test results indicate that the composite beam undergoes a sequence of four characteristic phases: elastic phase, crack propagation, fiber reinforcement and ultimate failure. The measured strain profiles are consistent with the hypothesis that cross-sections remain plane under loading. For the composite beam, the measured flexural capacity is 21.8% greater than the specified design value. When loaded to the serviceability stage, the maximum crack opening is under 50 micrometers. The deflection remains limited to less than l/600. Originality/value The optimized design achieves a balance among lightweight construction, high load-bearing capacity and low maintenance requirements, providing theoretical foundations and practical references for the broader engineering application of UHPC-NC composite structures.