The understanding and controlling of the restrained shrinkage is critical for the application of ultra high performance concrete (UHPC). This study made an analysis of restrained shrinkage mechanism of four kinds of UHPCs based on the direct tensile test accompanied with acoustic emission (AE) source location, free shrinkage test and restrained shrinkage test. The effects of UHPC tensile properties (strain softening or strain hardening) and high performance calcium sulphoaluminate (HCSA, a new kind of expansion agent) dosages (0%, 3% and 6% by mass of total binder) were investigated. The restrained shrinkage cracking mechanism of strain hardening UHPC and strain softening UHPC was analyzed based on AE analysis method under direct tensile loading. The results indicates that strain hardening UHPC shows multiple micro-defects to relax the restrained tensile stress marginally while strain softening UHPC shows several hairline cracks to relax the restrained tensile stress evidently. In ASTM C1581-04 ring test, the restrained shrinkage of strain hardening UHPC with HCSA dosage of 0%, 3% and 6% at 80d is 141 με, 96 με and 16 με, respectively. The HCSA expansion agent can effectively reduce the restrained shrinkage of UHPC and the influence on the structure.

Cable-stayed bridges have commonly been built for crossing large-span obstacles, such as rivers, valleys, and existing structures. Obtaining an optimum design for a cable-stayed bridge is challenging, due to the large number of design variables and design constraints that are typically nonlinear and usually conflict with each other. Therefore, it is a reasonable alternative to turn the large and complex optimization problem into two sub-problems, i.e., optimizing the internal force distribution by adjusting the cable prestressing forces, and optimizing the other sizing or geometrical parameters. However, conventional methods are lacking in efficiency when dealing with the problem of optimization of cable forces in the first sub-problem, under the circumstance that iteration between the two sub-problems is required. To address this, this paper presents a surrogate-model-assisted method to construct a cable forces predictor ahead of the structural optimization process, so that cable forces can be effectively predicted rather than optimized in each iterative round. Additionally, B-spline interpolation curve is adopted for variable condensation when sampling for the surrogate model. Finally, the structure optimization in the second sub-problem is performed by leveraging an optimization program based on particle swarm optimization method. The performance of the proposed framework is tested with a practical engineering application. Results show that the proposed method showcases good efficiency and accuracy. The theoretical raw material consumption of the towers and the cables is 32% lower than the original design.

This paper describes the concept of a novel stay cable with a Carbon Fiber Reinforced Plastic (CFRP) and steel composite section. In this concept CFRP core conserves all the advantages of CFRP materials such as light weight and high strength, while steel coat provides protection for the CFRP core and ensures reliable anchorage performance. The steel coat can reduce cost and provide higher stiffness than CFRP materials in some length range. Following this concept, several configurations were proposed for the composite structure. Effects of the key design parameter of the proposed stay cables, namely the ratio of the CFRP section area to the whole section area, were examined through a parametric study using analytical solutions. By doing this, an appropriate range of the ρ value was suggested. Factors that can affect the appropriate range of the ρ value, including the horizontal projected length of stay cables, cable force, and pylon height (i.e., vertically projected length of stay cables), were also studied. Finally, the feasibility of the proposed stay cables was conceptually verified. It was shown that the proposed stay cables could be an excellent alternative to the pure CFRP or traditional steel stay cables.

This paper introduces the mechanical and economic performance of cable-stayed bridges with ultra-high-performance concrete (UHPC) girders. Based on the determined general layout and structure system, aiming at minimizing material consumption and considering multiple constraints, the parametric analysis and optimization process of the UHPC girder were discussed. Subsequently, full-scale models of a 1,200 m cable-stayed bridge with UHPC girders and those with steel girders were established and analyzed under load combinations to evaluate their static mechanical performance. Additionally, the material consumption estimation equation was established to evaluate the economic performance of cable-stayed bridges. The economic performance of cable-stayed bridges with UHPC-girder scheme and that of steel-girder scheme were investigated and compared by theoretical calculation and finite element modelling. The results indicated that UHPC-girder cable-stayed bridges are highly competitive for super long-span cable-stayed bridges and represent a promising alternative for the design of large-span bridges in the future. This study provides valuable insights into the feasibility and potential of UHPC-girder cable-stayed bridges.

Bridges are typical structures that provide connections between destinations and therefore achieve transportation functionality

面对交通量日益增加的现状，双层交通拱桥因其良好的力学、施工和经济性能得到了广泛的应用。但目前对于双层交通钢桁架拱桥的讨论尚不够充分，且对于各类设计参数对于结构性能的影响研究存在不足。因此，本文以某大跨度双层钢桁架拱桥为研究对象，首先对四种索力优化方法得到的索力分布与成桥状态效果进行对比，分析不同方法的区别，明确了最适宜的成桥状态优化方法；进而研究了边中跨比、主梁桁高、主拱桁高等参数的变化对结构的影响，并深入探讨了其中的力学机理，通过总结规律，为同类型工程的设计提供了参考。