Initial Research On Mould-bag Steel Fiber Concrete Bracket Material Properties And Component Strength Characteristics

Bracket support is the common support method in roadway, which can effectively control the deformation of surrounding rocks.Considerring the advantages and disadvantages of traditional arch structure, steel fiber reinforced concrete and geotextile bag concrete, the mould-bag steel fiber concrete bracket support system which is low cost and convenient construction was developed and researched.In order to explore the mechanical properties of the core material(steel fiber reinforced concrete), the axial tensile and axial compression tests of steel fiber reinforced concrete specimens were carried out. The results showed that with the increase of fiber volume rate, the growth trend of steel fiber reinforced concrete axial tensile strength was more and more gentle, the axial compressive stress-strain curves became more and more plump; with the strength of the substrate concrete was increased from C30 to C50, the ultimate tensile strength of steel fibre concrete was increased by 31.6% and 68%, while the latter strength increased only 6.7% and 20%. Based on the theory of composite mechanics, the calculating formulas of elastic modulus and Poisson ratio of steel fiber reinforced concrete were deduced, and the size of the two varies with the external pressure, and the initial value is identical to the ordinary concrete. The compressive strength expression of steel fiber reinforced concrete was deduced, and the tensile strength expression of steel fiber reinforced concrete was improved. The steel fiber reinforced concrete constitutive curves were expressed with formula using damage constitutive model and data fitting method.In order to explore the strength characteristics of the bracket components, the axial compression short column test of different steel fiber volume ratio, concrete matrix strength, axial diameter ratio were carried out. The results show that when the axle diameter ratio was 2.25,compared with the short column of the grain concrete, when the volume ratio of steel fiber was 1%, 2%, 3%, the ultimate bearing capacity of the short pillar was increased by 9.9%, 13.4% and 19.7% respectively, and the corresponding peak displacement increased 7.5%, 12.5% and 29%respectively, and the slope of the descending section was -744, -441 and-302 respectively; In this, the larger the volume ratio of steel fibers, the higher the limit strength of the axial compressive short column components, the more obvious the plastic damage characteristics. When the steel fiber volume was 2%, the axial diameter ratio decreased from 3.3 to 2.5, from 2.5 to 2 o'clock, the limit strength of the short column components increased by 421KN, 546KN respectively, the residual strength increased 53KN, 406KN respectively; therefore, with the decrease of axle diameter ratio, the ultimate strength and residual strength of the short column components increased obviously. The strength of concrete substrate increases from C30 to C40, from C40 to C50, the limit strength increase of the short column member was 353KN,154KN, and the residual strength increment was 80KN and 84KN respectively. Visible as the strength of the concrete substrate increases,the limit strength of the short column components increased obviously,but the residual strength was not obvious.At the same time, the pure bending test were carried out to research the pure curved beam components of different steel fiber volume ratio,admixture material and restraint material. The results show that the flexural bearing capacity of concrete beams restrained by steel fiber +carbon fiber mesh cloth was 2.5 times times as much as the concrete beams. The flexural bearing capacity of the remaining type components(W-2-40-200-I, W-1-40-200, W-2-40-200, W-3-40-200) was 1.14 times times, 1.2 times times, 1.48 times times, 1.67 times respectively, the plain concrete beams. The peak deflection of the steel fiber + carbon fiber mesh cloth restrained beam component was 3.65 times times the plain concrete components, the purity steel fiber reinforced concrete material was followed. The peak deflection of the short-cut RC beams was only 1.02 times times of the plain concrete.Numerical experiment of axial compressive short-column and pure bending beams were carried out with ABAQUS numerical analysis software. The results show that the equivalent stress concentration area of the axial compression short column model gathers from the internal and lower ends of the model to the core, then the new equivalent stress concentration area continues to appear on the internal and lower ends of the model and gathers to the core, so circulating until the model destroys.The mechanical behaviors of the pure flexural beams with different concrete matrix strength are identical in the elastic stage, and the strength of the concrete matrix can be increased to improve the bending moment and the deformation ability of the component.The initial comparison between the support capacity and the cost of the mould-bag steel fiber concrete bracket, the U-steel bracket and the CFST bracket was carried out. The results showed that when the cross-section diameter of the mould-bag steel fiber concrete bracket was increased by one times, the supporting capacity was 1.56 times and 1.15 times respectively of the latter two, but the cost of each frame was only 44.5% and 41.4% of the latter two. The bracket has obviously advantageous in saving labor and materials, which can bring great economic benefit to the roadway support project.