Research On Tightness Measurement Method Of The Joint Plate For The High-strength Friction Bolt Connection Based On Ultrasonic Echo

With the promotion of the steel structure,the steel structure has been widely used in various fields,such as marine structures,railway bridges,buildings and so on.The high-strength bolt connection has become a common form for steel structures,and its function is to transfer the joint force through the friction force generated between the compressed connections under tension of the bolts.To test the tension force,the torque method is usually used with a torque coefficient which has a certain randomness.Such testing is valid only during construction and cannot be repeated.Based on the gusset plate of actual steel truss bridge,this paper proposes a new method to measure the quality of the connection,namely tightness between the between gusset plates,which detects the compression degree between gusset plates quantitatively according to the analysis of rough contact surface between gusset plates and the difference of reflection and transmission wave of ultrasonic at different compression degree,and then the tensioning force of the high strength bolt can be obtained.It provides an efficient method for the construction quality evaluation of high strength bolt joint plate,and also provides a nondestructive testing method to measure the technical status of the steel plate in the existing steel structure,which is of important application value.In the paper,it is showed that the fractal theory is of good accuracy,certainty and uniqueness to solve the problem of rough contact through the introduction and comparison of three kinds of analysis theory of rough contact surface.And then,the mathematical model of the contact pressure between the contact surface and the real contact area is established based on the fractal theory.In consideration of the characteristics of ultrasonic propagation in the splicing board and on the contact surface,the effect of ultrasonic attenuation on the results is considered during data processing,two loss rate indexes of both the primary echo and the second one,are defined,and the relationship between the ultrasonic echo loss index and the real contact area of the contact surface is established.According to the echo loss rate model,the variation curve of the ultrasonic echo loss rate with the tensile strength of high strength bolts are numerically solved in MATLAB with the results of the analysis of ABAQUS for joints under different working conditions.Two sets of gusset plate specimens are designed and manufactured.Under the condition of laboratory,the ultrasonic tests are carried out under different compression degree using compression test machine to simulate high strength bolt connection,the relationship between the indexes of ultrasonic echo loss,the inter plate pressure and the signal voltage is analyzed.Experimental results show that the ultrasonic data can accurately reflect the compression of the gusset plate when great pressure is applied,and the second echo loss rate is more advantageous when the ultrasonic intensity is large.So,the accuracy of the relationship between the ultrasonic echo loss rate and the tensile strength of high strength bolts is verified and the basis for the field test is provided.The 2 sets of plate specimens manufactured according to the standards for the design of the bridge are used to carry out ultrasonic experiments under different states of the screw with portable ultrasonic flaw detector,using the electric wrench to tighten the bolt at the construction site.The measured high strength bolt tensioning force is calculated using the method proposed in this paper and then it is compared with the field measured counterpart,the comparison results show that the accuracy of the proposed method is less than 5%,which can meet the requirement of the measurement precision of the high strength bolt tension in the project.It is showed that the detection method of ultrasonic echo for high strength bolt tensioning force,which is based on the ultrasonic echo loss rate in this paper,is of important application value for the overall performance evaluation of the constructing and existing high strength bolted friction connections and the testing of high strength bolt tension.