Sustainable multi-objective topology optimization of composite hybrid tubular trusses

Purpose The construction sector significantly contributes to global CO2 emissions, underscoring the need for structural optimization methods that explicitly integrate mechanical performance, cost, and environmental criteria. However, existing composite-truss optimization studies do not simultaneously couple truss topology and member sizing with composite slab geometry and reinforcement while considering these competing criteria. This work addresses the gap by developing an integrated multi-objective formulation for hybrid composite concrete–high-strength steel trusses, featuring a concrete-filled upper chord and simultaneous optimization of slab geometry with reinforcement. Design/methodology/approach Two assessment stages were conducted: (1) single-objective optimization across spans of 8–24?m to quantify the structural and environmental benefits of pairing hybrid trusses with optimized slabs; and (2) multi-objective optimization for the best-performing span from (1), including slab capacity as an explicit objective. Particle swarm optimization (PSO) and multi-objective particle swarm optimization (MOPSO) algorithms were used to solve the single- and multi-objective problems, respectively. Findings Results show that hybrid trusses combined with optimized slabs reduce emissions by up to 24% relative to the corresponding homogeneous trusses combined with catalog-based slabs, consistently select concrete strengths greater than 40 MPa for upper-chord filling, and achieve slab-depth reductions relative to the catalog-based slab configurations through reinforcement optimization. Compared with the minimum-CO2 solutions obtained using PSO, the selected MOPSO solutions provide improved slab load-bearing capacity with limited increases in emissions and cost. For usual loads ranging from 2 to 5 kN/m2, slab load-bearing capacity increased by up to 2.5 times relative to the MOPSO solution at 2 kN/m2 for the same span, with corresponding increases of up to 25% in CO2 emissions and 52% in construction cost. Higher load demands lead to substantial growth in both. Research limitations/implications The study focuses on medium-span structures (8–24 m) and considers a specific set of material grades and design assumptions, which may limit direct generalization to other structural typologies or boundary conditions. Future research could extend the formulation to larger spans and alternative composite configurations. Practical implications The proposed framework enables engineers to design more efficient hybrid truss–slab systems by explicitly balancing structural performance, cost, and CO2 emissions. The results demonstrate practical potential to reduce material use in slabs and to optimize concrete strength selection in composite trusses, supporting more sustainable design decisions in real-world applications. Social implications By reducing material consumption and associated emissions in structural systems, the proposed approach helps lower the environmental footprint of buildings. This supports broader sustainability goals in the construction sector, including climate change mitigation and more responsible use of natural resources. Originality/value This study introduces an integrated optimization framework that simultaneously couples truss topology, member sizing, and composite slab reinforcement design within a unified multi-objective formulation. Unlike previous studies, it explicitly links slab structural performance with hybrid truss optimization, providing a more comprehensive and sustainability-oriented design methodology.