Study On Bending Performance Of Fiber Reinforced Shotcrete Plate

In the high in-situ stress environment,sprayed concrete is prone to cracking or falling off under bending loads,which has a very adverse impact on the safety of tunnel construction.Improving the toughness of sprayed concrete and improving the bearing capacity of support structures has been a hot and difficult research topic in this field.In recent years,many scholars have devoted themselves to the research of fiber reinforced shotcrete to improve the stability and safety of concrete structures,and have obtained some practical applications in underground engineering.In previous studies,the toughening effect of fiber on concrete was mostly studied using three point bending or four point bending tests of small beam specimens,but the actual wet sprayed concrete shotcrete anchor structure is closer to the bending process of plate shaped specimens under concentrated load,and the relevant research on plate shaped specimens is not yet in-depth.This article mainly explores the impact of synthetic fibers on the deformation characteristics,failure process,and flexural toughness of concrete plate shaped specimens.The main research contents and conclusions are as follows:(1)The influence of fibers on the failure modes of concrete slab specimens under concentrated load is studied.The results show that polypropylene coarse fiber can effectively improve the crack formation and propagation characteristics of concrete slabs subjected to concentrated load bending,effectively inhibit the crack propagation speed of concrete slabs,and can still expand along the crack width direction after the occurrence of cracks,making them change from brittle failure to ductile failure.(2)The influence of fiber on the spatial distribution of stress and deflection of concrete slab specimens under concentrated load was studied using strain and deflection collection devices.The results show that the network structure formed by the random distribution of polypropylene coarse fibers in the structure can improve the transfer of stress inside the concrete slab,making the stress distribution inside the concrete slab more uniform,and facilitating the transfer of load from the weak unstable region to the stable region after the occurrence of cracks.Polypropylene coarse fiber has little effect on improving the initial crack load of concrete slabs,but can significantly increase the ultimate load of concrete slabs;With the increase of fiber content,the ultimate load of concrete slabs gradually increases;After reaching the ultimate load,the load of ordinary concrete slabs rapidly decreases to zero,and the concrete slabs mixed with fibers can still bear a larger load after reaching the ultimate load.(3)The influence and mechanism of reinforcement mesh on the failure mode and flexural toughness of concrete slabs were studied,and the differences between reinforcement mesh and polypropylene coarse fiber in toughening were discussed.The results show that the flexural toughness of fiber to concrete is mainly reflected in the cracking stage and the failure stage.With the increase of fiber volume content,the more obvious the toughening effect on the specimen is.Polypropylene coarse fibers mainly enhance the bending toughness of materials by enhancing the deformation ability of structures;The reinforcement mesh mainly enhances the flexural toughness of the structure by enhancing the strength of the material.Adding coarse polypropylene fibers into reinforced concrete can not only enhance the strength of the structure,but also enhance the deformation ability of the structure,making the flexural toughness significantly improved.(4)A program was developed to generate the three-dimensional random distribution of fibers,and a three-dimensional finite element model was established to analyze the stress state of fibers during the loading process.The results show that the fiber can bear the load together with the concrete matrix during structural deformation,and the fiber can transfer the load from the weak position of the structure to the stable region of the structure after cracks occur.