To study the relationship between the mutation segment of tension test curve and the clip bite force when using the lift-off method to test the force of prestressed steel strand, the high-frequency acquisition technique in the resistive pressure sensor was used to test the prestressed steel strand forces of a prestressed concrete beam under and outside the anchorage when the clip disengages. A total of 20 samples were tested. The clip bite force test scheme was designed. A total of 326 samples were tested and the statistical analysis was performed. The calculation formula for the clip bite force considering the tension was established. Through the verification test of 37 samples, the test accuracy of bite force correction results was studied. 257 samples were tested in the actual project, and the test results were compared with the proposed calculated formula results. Research result shows that the clip will break away from the original bite mark when the steel strand extends more than 4.5 mm. However, when the clip disengages during the actual test, the tension will be stopped in time, so the lift-off test will not change the effective prestress of prestressed steel strand under the anchorage and affect the project quality. When installing the clip, if the clip does not completely fit the taper hole of socket, the clip will have a large elastic pressing force in the lateral direction to form an additional friction force. The friction force will completely disappear when the clip is separated from the socket. The change of tension outside the anchorage is not obvious at this moment, so the slope of descending segment of tension test curve obtained by the lift-off method has a dispersion after the peak tension, and it is related to the clip installation precision. The bite force of socket in the lift-off test consists of the transient internal force redistributions under and outside the anchorage. The proposed calculation formula for clip bite force can eliminate the test error caused by the bite force between the clip and the socket, and improve the test accuracy by 6.78%. The test bite force in the actual project is larger than the mutation segment of tension test curve obtained by the lift-off method. Therefore, when using the lift-off method to test the prestressed steel strand, the effective prestress under the anchorage is the difference between the peak value of tension test curve obtained by the lift-off method and the bite force. © 2019, Editorial Department of Journal of Traffic and Transportation Engineering. All right reserved.
