Mechanical Characteristic Analysis Of Anchoring Steel Bar During Pull-out And Double Shear Tests

Anchoring steel bars have a significant influence on concrete and jointed rock masses structure.If the anchor force fails,anchoring structure will damage due to no resistance ability.Thus,it is necessary to research the mechanic characteristics of anchoring steel bars to evaluate structural stability.In order to study the anchoring mechanism and the failure modes between the grout and steel bar,a series of pull-out tests and fully grouted steel bar double shear tests were carried out.The grout cracks expansion,anchorage force-displacement relationship during pull-out tests and the mechanic characteristics of steel bars and resistance ability of shear plane in jointed rock masses were analyzed by theoretical analysis and numerical simulation.The main research results as follows:(1)The pull-out test show that the grout front transverse rib displayed wedge-shape damage and the grout exhibited radial splitting failures in the pull-out test under low confining pressure.The anchoring force of the transverse rib bar increased with the grout strength increasing and it did with the effective transverse rib angle increasing.The double shear tests show that the stress states of the fully-grouted steel bar on both sides of the shear plane were opposite.The shear force of the fully-grouted steel bar increased with the shear displacement increasing and the relationship curve of shear-force and shear displacement show a apparent staging character.The analytical expressions of shear force and axial force of the bolt showed the linearly variation with the shear displacement increasing.The shear force was much greater than the axial force and the shear force predominated in the shear test.(2)Base on the pull-out tests,the anchorage grout during the pull-out tests displayed the splitting failure mode and the relationship curve of anchorage force-displacement can be simplified into four stages: debonding stage,ascent stage,splitting stage and residual stage.Then the analytical derivation and segregate expressions to the relationship curve of anchorage force-displacement at different stages were carried out by using the nested cylinder model.Furthermore,the numerical simulation results verified that the grout in front of the transverse rib presented the wedge-shape force and the anchorage grout displayed the splitting failure mode ultimately.(3)Based on the double shear tests,the elasto-plastic characteristics of the fully-grouted bolt under double shear tests were verified by the simplified analytical model.Moreover,the sensitivities of influence parameters of the fully-grouted bolt performances by the numerical analysis were analyzed.The analytical result show that the confining pressure on the shear strength of the fully-grouted bolt is the most significant factor,the strength of the jointed rock is the second,and the jointed surface parameters have the least effect.From the above analysis result,it is concluded that the mechanical characteristics of anchor reinforcement effect on the stability of anchorage structure,which provides a theoretical reference for engineering practice of anchoring concrete and joint rock masses.