| Local structures of large concrete bridges are in a complex stress state with large tensile stress, such as 0# section and closure section of continuous rigid frame bridge, which causes cracking and affects durability of bridge structures. More engineering practice shows that using ordinary high strength concrete to improve material strength can not meet the crack resistance and durability requirements of bridge structures. High strength and high ductility are the development trend of material performance requirements in civil construction and transportation area. Therefore, this study starts with the mechanical properties of materials and conducts the secondary development of "steel fiber reinforced polymer modified concrete" with independent intellectual property rights to develop a new composite material named steel fiber polymer high strength structural concrete which can be used in long-span bridges. C60 concrete was used as reference material to discuss basic mechanical properties, crack resistance behavior, temperature fatigue properties and durability of the new material. Research results have important scientific significance and engineering application value for disaster prevention, repair and enhance the structure durability of long-span bridges in constructions and services. The main study content and conclusions were as follows:1) Research and development of "steel fiber polymer high strength structural concrete" (SPHSC) which is a new composite material used in long-span bridge structures. In premise of ensuring basic mechanical properties and functions of the bridge structures, modified concrete material called SPHSC which has similar strength of the existing high strength concrete such as C60 concrete and better behaviors of cracking resistance, fatigue resistance and durability through a lot of mix design, material composition and mechanical properties of macro and micro analysis.2) Cracking resistance study on "Steel fiber polymer high strength structural concrete". Considering the inherent defects of concrete materials, in this paper, fracture toughness was taken as the main cracking behavior indicator. Combination methods of both experimental and theoretical analysis were used. Fracture toughness in non-geometric similarity condition of SPHSC was tested. Effects of characteristic size of the specimen (beam height H), relative height of the initial crackα0 and material composition on the fracture toughness on fracture toughness were discussed. Micro toughening mechanism of steel fibers and polymer were analyzed. Size effect formulas of single K and double K fracture toughness of high strength concrete under geometric and non-geometric similarity conditions were deduced based on Bazant scaling law and verified by tests. The results show that SPHSC has better crack resistance compared with C60 concrete. The size effect formulas of fracture toughness derived in this paper is valid, and its predictive value agrees well with the experimental data.3) Fatigue resistance study on "Steel fiber polymer high strength structural concrete". On basis of experimental study, comparative analysis was used. Under room temperature and five load levels, fatigue behavior of SPHSC and C60 concrete which has similar static mechanical properties and fatigue mechanism of adding material were discussed. The results show that SPHSC has better fatigue resistance compared with C60 concrete for adding of steel fibers and polymer. Fatigue limit of SPHSC from S～N test curves increases 31.3% compared with that of C60 concrete. This is a great contribution to bridge fatigue performance and durability.4) Temperature fatigue behavior study on "steel fiber polymer high strength structural concrete". First, according to the classical theory of fatigue strength and assumptions, temperature fatigue life expressions of SPHSC were derived. And then, constant coefficients in the expressions were determined by temperature fatigue tests using SPHSC material under 3 working temperatures (20℃, 50℃,80℃) in accordance with subtropical climatic conditions and four load levels. The results show that fatigue resistance behavior of SPHSC changes with working temperatures and decreases when working temperature is relatively high. Using the semi-empirical formula proposed in this paper, the temperature fatigue life and fatigue limit of SPHSC material in working conditions of the subtropical climate area can be effectively and easily presumed.5) Structural mechanics and durability analysis of SPHSC box girders. SPHSC of this research was used in 0# and closure sections of a long-span continuous rigid frame cantilever bridge in a super highway. Analysis of bending capacity, shear strength, crack resistance and durability of SPHSC box girders have further confirmed the excellent structural mechanical properties and construction behavior of SPHSC material developed by this research group and achieved the purpose of research and development of the material.
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