Research On Axial Force Test Method Based On Vibration Characteristics Of Concentrated Anchor Bolt

Concentrated anchor bolt is widely used in various geotechnical engineering in China.Its main purpose is to support the surrounding rock of roadway,maintain the stability of surrounding rock,maintain the normal working state of roadway during service and avoid safety accidents.The construction quality is highly concerned by the owner and government regulatory departments.The technical code for geotechnical bolt and shotcrete support engineering stipulates that the special and comprehensive class A Laboratory of highway engineering bridge and tunnel must be equipped with bolt quality detector and have the ability to test the axial force of bolt.However,the axial force test of tunnel and slope anchor bolts is still carried out by embedding force measuring sensors or pasting strain gauges in the anchor bolts in advance and measuring through special reading instruments.Its axial force test method is one of the common means of scientific research,but its test method is complex and the cost is high,so it can not realize the universal supervision of project quality.Therefore,it is necessary to study a simple,efficient and widely used axial force test method.Frequency method is a low-cost and efficient nondestructive testing method,which can quickly and effectively detect the effective tension of prestressed anchor bolt,and is widely used in the detection of vertical prestress of bridge.It is obvious that the anchorage method of prestressed anchor rod is similar to that of prestressed anchor rod,but it is still different from that of prestressed anchor rod.Referring to the test method of vertical prestressed finish rolled deformed steel bar of bridge,this paper plans to study the axial force detection method of anchor rod by using the frequency method.According to the stress characteristics of anchor rod anchorage system,indoor model test is designed,and three simplified models are proposed based on the centralized anchorage system to study its vibration characteristics,form the contact stiffness tension fitting curve,and realize the axial force test of centralized anchorage anchor rod based on the frequency method.The main work and achievements are as follows:(1)Establish the indoor concrete beam model,study and analyze the relationship between the excellent frequency of the unstressed section and the tensioning force and the unstressed length,and analyze the relationship between the excellent frequency of the unstressed section and the vibration frequency of the tensioning section;(2)Based on reasonable assumptions,three simplified models are proposed to obtain the frequency equation.Based on the inherent relationship between the contact stiffness and the monotonic increase of the normal stress of the contact surface,a fitting formula of the relationship between the normal stiffness of the contact surface and the tension of the anchor rod is formed.(3)Based on the above model,the influence factors of high tension,with or without ball pad,butterfly tray contact object and tension section length on the relationship between normal stiffness of contact surface and bolt tension are studied;(4)Carry out the simulated field test,compare the data with the indoor model test database,and study the applicability of the bolt axial force nondestructive test scheme in practical engineering.