No abstract

Steel-concrete composite pylons are rarely used in long-span cable supported bridges. This paper introduces a new type of steel-concrete composite pylon, which is applied to a cable-stayed bridge with a main span of 600m. For this new type of pylon, the steel shells are connected with concrete through PBL shear connectors and studs, and the inner steel shells are connected with the outer steel shells by angle steels. Numerical analysis and full-scale model tests show that the pylon structure exhibits excellent mechanical properties and construction performance. On the other hand, highly factory-manufactured modular assembly of the reinforced steel shell structure can effectively reduce the intensity and difficulty of on-site operations, and improve the quality of the project, with low construction risks. Whereas, the modernization level of the construction of the cable pylon has been greatly improved.

Ultra High Performance Concrete (UHPC) has gradually become the most promising high-performance material, and has achieved good results in the field of impact and explosion protection engineering. In general, normal reinforced concrete (NC) beams subjected to impact load are prone to local punching shear failure. Although pure UHPC beams can improve their impact performance, their further application is limited by the high cost. In order to achieve the balance between impact resistance and economy, this study puts forward the design scheme of local replacement and wrapping with UHPC to improve the impact resistance of reinforced concrete beams. In this work, the different research conditions including NC beam, UHPC beam and NC-UHPC composite beam are designed, and the impact resistance of specimens is compared and analyzed. The results show that UHPC local replacement scheme can effectively avoid local punching shear failure of beams. As for the UHPC wrapping scheme, the failure mode of the beam changes from punching shear failure to bending failure. Compared with NC beams, two schemes can effectively reduce the peak displacement and residual displacement in the mid-span. The peak displacement and residual displacement in the mid-span of the UHPC local replacement beam are smaller than that of UHPC wrapping schemes, and the mid-span bearing capacity is better. In this work, it is recommended to take a local replacement length greater than 2 times the beam height to avoid local punching shear failure.

This paper introduces a new type of steel-concrete composite pylon that has been applied to Nanjing Fifth Yangtze River Bridge (a three-pylon cable-stayed bridge with a main span of 600 m). For this new type of pylon, the steel shells are connected with concrete through PBL shear connectors and studs, and the inner steel shells are connected with the outer steel shells by angle steels. Numerical analysis and full-scale model tests show that the pylon structure exhibits excellent mechanical properties and construction performance. The application of BIM technology, the research and development of special spreaders and construction platforms ensure the precise installation of structures. Highly factory-manufactured modular assembly of the reinforced steel shell structure can effectively reduce the intensity and difficulty of on-site operations, and improve the quality of the project, with low construction risks. Whereas, the successful application of this steel-concrete-steel sandwich composite pylon marks the formation of a complete set of construction technology of steel-concrete-steel sandwich composite pylon, which can be widely used in similar bridges.

This paper aims to study the influence of key design parameters (e.g., reinforcement ratio, cover thickness, stud spacing, and thickness of the ultra-high-performance concrete (UHPC) layer) on the longitudinal and transverse bending performance, as well as the cracking load and ultimate bearing capacity calculation theory of steel–UHPC lightweight composite deck (LWCD) structure. Four transverse bending tests and four longitudinal bending tests on steel–UHPC composite plates and steel–UHPC composite beams were conducted, respectively. The refined finite element models of components with different key design parameters based on ABAQUS were established. The influences of different key design parameters on the transverse and longitudinal flexural behaviors (e.g., load-mid-span displacement curve, cracking stress, stiffness, elastic limit load, critical slip load, ultimate bearing capacity and ductility) were compared and analyzed in detail. The ultimate bearing capacity can be improved by increasing the thickness of UHPC layer and the reinforcement ratio of longitudinal reinforcement, and reducing the cover thickness and the spacing of studs. According to the longitudinal bending characteristics of the steel–UHPC lightweight composite deck structure, the calculation formulas for the cracking load and the ultimate bearing capacity of the steel–UHPC composite beam are proposed, and the calculated values are in good agreement with test results (the errors are basically within 10%), which is convenient for practical engineering applications.