In the determination of the tensile stress relaxation performance of the steel strand at ambient temperature (20℃± 2℃), the measurement parameters are the relaxation rate of 5min, 10min, 30min, 1h, 2h, 4h, 8h, 16h, and 24h. Record the relaxation rate every 24h until 100h, and then calculate the relaxation rate at 1000h based on the relationship between the relaxation rate and time. Relaxation testing machine: range 0-300kN, relative error is 0.01kN, microcomputer control system, steel strand anchorage, diameter 15.2cm; 12.7cm; temperature sensor, resolution is less than 0.5℃, relative error is ±1℃ .
Preparation stage: Calculate the preloading force value and initial loading force value of the relaxation test according to the results of the same coil tensile test and the specification of "Steel Wire for Prestressed Concrete". Before the relaxation test, the air conditioner should be turned on and the temperature of the test room should be stabilized at 20°C±2°C, and the 2.5-meter steel strand sample should be placed for more than 4 hours.
Test steps: Turn on the relaxation machine and computer, automatically connect the amplifier Tianjin prestressed anchorage and preheat the amplifier for more than 15 minutes, enter the relaxation test system interface, fill in the test data and confirm it as required. Adjust the position of the tension screw, insert the test piece into the center hole of the tension screw and the tension frame, install the anchors at both ends and pay attention that the outer end of the tension screw should protrude about 30mm from the outer end surface of the casing.
After zeroing the amplifier, click on the preload with the mouse to apply the pre-stretching force to the set force value. The automatic relaxation test arrives and stops automatically. For the automatic relaxation test, press the preload button on the control panel of the relaxation machine to apply pressure until the set force value is stopped. Adjust the centering of the steel strand to the central axis of the tension direction of the relaxation machine. Click the mouse to load the initial load, increase the initial load to the theoretical initial load at a uniform speed, and complete the application within 3 to 5 minutes.
hold the load for 60 seconds, and then automatically transfer to the relaxation test. When the test is stopped, the system defaults to 100 hours. By clicking and data analysis, the test data is fitted and calculated and the fitting formula and line segment are displayed. By clicking the extrapolation calculation, the extrapolation calculation is performed and the calculated value is recorded. The system defaults The time is 1000 hours. After unloading to 0.0kN, press the machine button to remove the anchor and the steel strand, and close the system software.