## 6 Conclusions  
1. This study proposes standardized design criteria for a bottom-supported ultra-high-performance rectangular concrete-filled steel tube composite truss bridge with a length of 110 m. The design features a height-to-span ratio of 1/8.1, a width-to-span ratio of 1/6.1, and a span length of 15.5 m. The chord members utilize PBL-stiffened steel tubes with ultra-high-performance concrete infill, and prestressing tendons are tensioned within the concrete of the lower chord. The web members are designed with a rectangular cross-section, and the bridge deck system incorporates longitudinal and transverse beams with precast deck panels. The construction methods proposed include lifting and pushing techniques. This standardized design approach, combined with factory prefabrication and assembly construction, aims to minimize onsite work, reduce the environmental impact during construction, and achieve rapid bridge assembly, providing a reference for designing prefabricated bridges in large-span highway applications. 2. The load conditions of the proposed design during both bridge completion and construction phases are analyzed using finite element software. The results indicate that, under vehicle loading, the main truss deflection reaches 216 mm. Under the most unfavorable loading condition, the maximum stresses at the main truss nodes are \(-\)164.6 MPa for the upper chord, 34.3 MPa for the lower chord, \(-\)244.9 MPa for the compressed web members, and 215.9 MPa for the tensioned web members. Under fatigue model I, the maximum normal stress amplitude for the main trussmembers is 34.81 MPa. The strength, stiffness, and stability checks of the proposed design meet the relevant code requirements. * Compared to the original design, the proposed scheme reduces the safety factors of the upper chord, compressed web, and tensioned web members by 12.8%, 29.5%, and 28.7%, respectively, while ensuring structural safety. This results in a significant improvement in material utilization. Additionally, the proposed design reduces steel usage by 23.5%, concrete usage by 11.6%, and total costs by 17.29%, demonstrating superior economic benefits. * Compared to steel truss bridges, the composite truss bridge with ultra-high-performance concrete inside the chord members improves the components' load-bearing capacity and ductility while reducing steel usage. It prevents potential buckling issues of the steel tube walls during construction, making the process more convenient. No temporary support is needed, saving materials and labor costs and reducing the construction time. Additionally, the concrete-filled steel tube structure offers better corrosion resistance, fire resistance, and seismic performance than steel tube structures, leading to lower maintenance and operation costs. Therefore, the composite truss bridge is more economically advantageous. Although composite truss bridges have been employed in some projects, issues such as node fatigue, cracking of under-deck panels, and high-strength material matching require further research. Conceptualization, S.S. and L.J. ; Methodology, S.S.; Validation, L.J. ; Formal analysis, S.S.; Investigation, Y.D. ; Resources, Y.D. ; Data curation, Y.D. and Z.L. ; Writing--original draft, S.S.; Writing--review & editing, L.J., Z.L. and R.P. ; Visualization, R.P. ; Supervision, L.J. All authors have read and agreed to the published version of the manuscript. This research was funded by National Natural Science Foundation of China grant number 52478125, Fundamental Research Funds for the Central Universities grant number 300102213207 and Overseas Students Science and Technology Activities Project Merit Funding in Shaanxi Province (2021-11). Not applicable. Data Availability Statement: Data is contained within the article. Authors [PERSON], [PERSON], [PERSON] and [PERSON] were employed by the company Shandong Expressway Infrastructure Construction Co., Ltd.