Construction in high-density urban areas necessitates rapid execution and enhanced structural integrity, driving the innovation of precast composite enclosure structure (PCES) that integrates the advantages of precast and cast-in-situ technologies. However, quantifying sustainability benefits and determining optimal precast thickness for PCES remain challenging, often causing structural overcapacity redundancy or safety compromises in emission-reduction efforts. This study proposes a sustainability efficiency assessment model integrating carbon-mechanics and cost-mechanics, investigating PCES performance under varying precast thicknesses in terms of sustainability per unit flexural capacity. Key findings include: (1) PCES with minimum precast thickness exhibits comparable usage-stage flexural capacity (1217.98 kN m) to conventional cast-in-situ enclosure structures (1216.19 kN m); (2) PCES reduce greenhouse gas emissions by 12.89 % and costs by 12.41 %. Interestingly, both emissions and costs rise with increasing precast thicknesses due to heightened precast production and transportation demands; (3) For PCES adopting normal concrete, a 50 % precast-to-total thickness ratio optimizes the balance between flexural capacity and sustainability, increasing emissions and costs by merely 1.10 % and 0.67 % while enhancing flexural capacity by 1.47 % compared to the lowest-emission-cost scheme. This demonstrates the sustainability efficiency model's effectiveness in mitigating single-indicator decision biases; (4) High-performance concrete with ≥10 % reduced emission coefficient reverses the emission trend, enabling optimal sustainability efficiency at maximum allowable prefabricated thickness. This study presents an innovative sustainability efficiency assessment framework for PCES, offering theoretical guidance for high-performance, low-carbon and cost-effective structural design. • Integrating GHG emissions, cost, and bending resistance to assess the sustainable efficiency of PCES. • Interestingly, PCES's emissions and costs increase with rising prefabricated thickness. • Optimal sustainability efficiency at 50 % structural prefabrication thickness. • ≥10 % emission factor reduction for prefabricated concrete shifts optimal thickness determination.
He et al. (Tue,) studied this question.