Research For The Load-transfer Mechanism And Anchorage Properties Of The Glass Fiber Reinforced Plastic Anti-floating Anchor

Due to the poor corrosion-resistance,the durability of steel anti-floating anchor is questioned in the underground environment with rich corrosive ions.With the better dielectricity and corrosion-resistance,the Glass Fiber Reinforced Plastic(GFRP)anti-floating anchor has become one of the best replacements of the steel anchor.With the Fiber Bragg grating sensor testing technology and through the methods of theoretical derivation and experimental research,the paper studied some properties of GFRP anti-floating anchor in the inner-anchorage section such as the stress distribution rule along the anchorage depth,the load transfer rule in the anchorage body,the displacement rule of the head of anchor,and the critical anchorage length.Additionally,the external-anchorage section properties of the straight and bending GFRP anti-floating anchors such as bearing capacity and displacement rule are also researched.The research provides a theoretical and practical reference for the application of GFRP anti-floating anchor.The main research contents are as below:1.On the basis of the load-transfer theory and Kelvin displacement solution,we derived the distribution function of the GFRP anti-floating anchor rod body and compared with a pullout test for 2 GFRP anti-floating anchors.The comparison results show:(1)The theoretical curves of the axial force and shear stress are similar to the test results,proves the practicability of the method mentioned above.Due to the unevenness of the anchorage body and debonding effect of the anchor near the head of the hole,however,the main distribution range of the test axial force and shear stress is bigger and deeper than the theoretical results and the test shear stress maximum value is lower than the theoretical value.(2)In order to reduce the error between the test and theoretical results,we presented the average shear stress attenuation method under the fixed debonding length and the method of moving down the elastic section to correct the theoretical axial force and shear stress distribution function.The accuracy of the revised load-distribution curves promoted obviously.2.With the Fiber Bragg grating sensor testing technology,we successfully monitored the distribution for the axial stress at the different cross section and the shear stress at the different axial interface of GFRP anti-floating anchor under the pullout load.Furthermore,we analyzed the load transfer rule in the anchorage body and the displacement change rule of the head of the anchor.Test results show:(1)The bearing capacity of the GFRP anchor with rupture failure model is higher than that of the anchor with the slip failure model.The load-displacement curve of the GFRP anchor body with slip failure model occurs an uptrend phenomenon,hence,the displacement of the GFRP anchor body with slip failure model is higher than the anchor with rupture failure model.Increasing the anchor body diameter is beneficial for improving anchor bearing capacity and limiting the anchor body displacement.(2)The load-displacement difference curve of the anchor body and anchorage body of the GFRP anchor with slip failure model is higher than that of the anchor with the rupture failure model.Increasing the anchor body diameter is beneficial for reducing the displacement difference of the anchor body and anchorage body.(3)The distribution of the axial stress on the monitored cross-section in the inner-anchorage section,reduced along the anchorage length,shows a reversed-S form along the anchorage length direction.The shear stress of the axial interface promotes firstly and then reduces to 0 near the critical anchorage length,and the shear stress transfers from the first interface to the second interface with an obliquely upward direction.(4)The displacement difference of the anchor body and anchorage body,calculated by the simplified model for the distribution of the shear stress,meets the anchor using requirement,and the theoretical result is similar to the test result of the GFRP anchor with slip failure model.3.We deduced the analytical function for critical anchorage length of GFRP anti-floating anchor based on the concentric thin-walled cylinder shear model and simplified shear stress distributional model of the anti-floating anchor.The rationality of the above analytical calculation method and the basic hypothesis is verified by comparing the actual test results and phenomena.What's more,we made some other understanding that:(1)When designing the GFRP anti-floating anchor,2/3 of the theoretical critical anchorage length is taken as the reference value of the actual anchorage length of GFRP floating anchor,which can improve the material utilization and guarantee the bearing capacity at the same time,reduce the project cost.(2)The theoretical critical anchorage length will increase with the increase of the elasticity modulus ratio of the anchor bolt and rock-soil mass and the increase of the anchor bolt radius,which has practical value.4.Different types of reinforcement and GFRP floating anchor were fixed to the inverted concrete floor,and we conducted a pullout test to research the external-anchorage section performance of GFRP anti-floating anchor body.The test results show:(1)Bending treatment can effectively solve the problem of short anchorage length of steel anchor in concrete floor,but the bearing capacity of bending GFRP anchor reduces obviously due to the lower mechanical properties at the bending location of GFRP anchor.The longer the bending length is,the more obvious decline of the bearing capacity.(2)The longer the diameter and anchorage length of the GFRP anchor is,the higher the bearing capacity will be,which is explained reasonably from the perspective of anchor load-transfer mechanism and proved by introducing the generalized efficiency coefficient.(3)Bending treatment could limit the displacement of the steel and GFRP anti-floating anchor and reduce their deformation,and the longer the bending length is,the more obvious the limiting effect shows.Additionally,the displacement of GFRP anti-floating anchor body will reduce with the increase of the anchorage length.(4)Introducing the anti-floating anchor bending effect coefficient to illuminate that bending treatment is not conducive to the lifting of the bearing capacity of GFRP anti-floating anchor.Due to the bending treatment can effectively limit the displacement of GFRP anti-floating anchor body in the concrete floor,however,it is necessary to further study and determine the optimal bending form of GFRP anti-floating anchor.