| As a kind of high-performance construction concrete material, fiber reinforced concrete (FRC) has been widely used in the domain of engineering construction. High strength and high performance become the developing and application trend of FRC today. According to the instruction of China Association for Engineering Construction Standardization, the compilation group organized by Dalian University of Technology make a wholly adaptation to the "Specification for Design and Construction of Steel Fiber Reinforced Concrete Structures (CECS 38:92)". Therefore, the "Technical Specification for Fiber Reinforced Concrete Structures (CECS 38:2004)" is compiled. As a part of the revisal project, a special study on the bond-slip characteristics between steel fiber and high-strength mortar, as well as on the mechanical properties of high-strength SFRC, is performed with experiment. This paper analyzes the bond mechanism on the interface between steel fiber and matrix. The strengthening and toughening function of steel fiber on high-strength concrete is also studied. Furthermore, a new designing method of SFRC industrial ground floors is suggested, taking the toughness of steel fiber reinforced concrete into account.(1) A serials of pullout tests of steel fiber from high-strength mortar of 4 strength grades are accomplished. 5 kinds of fiber are used in these tests, thereinto 4 kinds were profiled. Based on the test data, the bond-slip characteristics between steel fiber and mortar matrix are analyzed. The effects of several parameters, such as the matrix strength, the fiber type and the fiber strength, on the bond-strength and failure form are studied. The applicability of a kind of steel fiber to certain matrix strength is suggested. During the analysis, it is found that the effects of the rising of matrix strength on adherence and generalized friction are higher than on the other components of bond stress. The influences of fiber aspect and matrix strength on the pullout curves and pullout works are studied. When fiber breaks, the toughnees of the bond between matrix and steel fiber is rapdly reduced. Formulas of bond strengths between high-strength mortar and different kinds of steel fiber are statistically regressed with test data.(2) To enlarge the application scope of concrete strength grade of the former Specification (CECS 38:92), large quantities of experiments have been carried through to analyze the behaviors of steel fiber reinforced high-strength concrete under compression, tension, flexure or shear. The effects of fiber aspect, fiber strength, fiber content and matrix strength on the mechanical properties of high-strength SFRC are analyzed. On the base of thecomplex material theory, the ultimate strength formulas of SFRC under the stress conditions mentioned above are statistically regressed. The load-displacement curves of SFRC under uniaxial tension and flexure are analyzed, and a unitized model to evaluate the toughness of SFRC is given. Relational expressions between split strength, tensile strength and flexural strength are educed. With the statistically regressing of the test data, a constitutive equation of SFRC under uniaxial tension is educed. Furthermore, an expression is given to quantify the relationship between flexural crack strength and flexural ultimate strength. A new formula is educed to calculate the shear strength of SFRC, and the formula 1 value well fits the test date.Some conclusions have been draw during the analysis. When be used in construction members to bear compression, steel fiber with large aspect ratio, high strength and minor diameter may be more effective. It is more effective of increasing fiber content on improving the tensile strength of high-strength concrete than on that of common -strength concrete. But as matrix strength rising, the ratio of tensile crack strength of SFRC with certain content of fiber is almost unchanged. The flexural crack strength of SFRC is hardly influenced by fiber type, but the flexural ultimate strength is strongly influenced by fiber type. Through comparing several methods for evaluation criterion of the flexural toughness of SFRC. one of them is selected. The method is not only objective and accurate, but also be easy to calculate. So it is compiled into the "Technical Specification for Fiber Reinforced Concrete Structures (CECS 38:2004)". Another point to notice, the shape parameters of the cross section of steel fiber has much influence on the shear strength of SFRC.(3). Based on the pullout tests, the bond-slip mechanism on the interface between steel fiber and matrix is particularity analyzed. On the base of Cox shear lag theory, SFRC is analyzed as a three phase complexes (reinforcing phase, reinforced phase and interface phase). With refined mechanical deducing, a new bond-slip model between profiled steel fiber and high-strength mortar is educed. Combined with the mechanical property tests and bond-slip model deduced above, strengthening and toughening mechanism of profiled steel fiber on high-strength concrete is systematically analyzes on the base of complex material theory. Finally a new constitutive model of bond-slip between steel fiber and matrix is built.(4). Aim at the vacancy of the design theory on SFRC industrial ground floors in our country, a new design method is given which takes the toughening function of steel fiber into account. This method is based on Meyehoff yield line theory of slab on elastic ground base and "Code for Design of Building Ground Engineering (GB 50037)", refer to the "Concrete Society Technical Report 34: Concrete Industrial ground floors" of the concrete society of England. The formula for SFRC floor slab thickness under many kinds of load conditions are given in this method, in which the effect of the toughness of SFRC after crack is adequatelyconsidered. This content has been compiled into the 10th chapter of the "Technical Specification for Fiber Reinforced Concrete Structures (CECS 38:2004)".
|
PDF Full Text Request