Study On Creep Characteristics Of BFRP Anchor In Clay Soil

BFRP bar is a kind of high performance material with light weight,high strength and good corrosion resistance,which can be used in geotechnical reinforcement instead of traditional anchor rods.It effectively solves the problem of poor durability of traditional steel bar anchors and has a large space for development.On the basis of previous studies,the creep tests of 4 groups of BFRP anchors and 2 groups of steel bar anchors were carried out in this paper.Through the comparative analysis of changing the grouting material and diameter of the test anchors,the long-term pullout resistance and creep constitutive model of different types of anchor are studied.The main research contents and results are as follows:(1)The creep test of BFRP anchor is carried out by using a self-made test device and the results show that the load of the initial creep of the anchor is 40% of the ultimate drawing force,and the failure load is about 75% of the ultimate drawing force.(2)Two commonly used creep empirical models are introduced and applied to this test.According to the test data,three kinds of creep empirical models are established in different functional forms,and the five empirical models are compared and analyzed.It is found that the empirical model based on power-hyperbolic function is the best to describe the creep ability of anchor,and the description ability of the model to the deceleration creep stage is enhanced by modifying the time function in the model.(3)Through the isochronal curve method and stable creep rate method,it is determined that the long-term pullout resistance of the anchor is about(0.55-0.65)instantaneous pullout resistance.Compared with the diameter of the grouting body,the effect of the grouting material on the long-term pullout resistance of the anchor is more obvious,and when the grouting material is made of cement paste,the creep displacement and long-term pullout resistance of the anchor are better than that of cement mortar.(4)The common component combination model is introduced,and the generalized Burgers model is improved by fractional calculus and damage variables.The improved nonlinear model can describe the whole stage of creep.(5)Compared with the steel bar anchor,the results show that: The creep characteristic of BFRP anchor is stronger than that of steel bar anchor,and the brittleness of steel bar anchor is stronger;The change of grouting diameter determines the long-term pullout resistance of the two kinds of anchors.When the diameter is small,the BFRP anchor is better than the steel bar anchor,and the diameter increases,and the long-term pullout resistance of the two kinds of anchors is almost equal;When the drawing force is lower than 0.8,the accuracy of the empirical model is better than that of BFRP anchor,and when the drawing force is higher than0.8,the accuracy of BFRP anchor is better than that of steel bar anchor;When the nonlinear creep model describes the two kinds of anchors,the steel bar anchors are more sensitive to instantaneous load and there is a great difference between the two kinds of anchors in the deceleration creep stage.