Experimental Verification Of High-precision Loading Control Method For Loading System With Three Degrees Of Freedom

At present,a three-degree-of-freedom loading system is often used to simulate the seismic response of engineering structures under various conditions.As the size of the structural test specimens becomes larger and larger,the boundary conditions become more and more complex,and the accuracy requirements of the loading system are correspondingly higher.The three-degree-of-freedom loading test is controlled by its affiliated MTS 793 software.The relevant parameters in the test change,and the internal program needs to be modified accordingly.Therefore,it is complicated and inconvenient to implement the test through the built-in calculation editor.And for the force-displacement mixed control method considering the geometric nonlinearity,its computational ability is limited.Therefore,the main research contents and conclusions of this paper are as follows:(1)Perfect and improve the three-degree-of-freedom quasi-static test loading control software.Use the software for numerical simulation,The simulation results show that: The results of the software are accurate.It is connected to the MTS 793 software and applied to the actual test to verify the reliability of the software.The test results show that: The three-degree-of-freedom quasi-static test loading control software has strong reliability in actual test control,and the operation is convenient and simple.(2)The three-degree-of-freedom quasi-static test was performed using the control software to verify the accuracy of the force-displacement mixed control(based on actuator feedback in the vertical direction)method based on the feedback of the external displacement sensors.The test results show that: The actual horizontal displacement of the specimen has a significant error with the target horizontal displacement.The error between the actual corner of the specimen and the target corner is more obvious.The force-displacement mixed control(based on actuator feedback in the vertical direction)method based on the feedback of the external displacement sensors does not allow the actual response of the specimen to track the corresponding target command well.(3)The three-degree-of-freedom quasi-static test was performed using the control software to verify the accuracy of the force-displacement mixed control(based on LVDT feedback in the vertical direction)method based on the feedback of the external displacement sensors.The test results show that: This method is effective and feasible when using the variable horizontal displacement fixed-axis force instruction with zero angle command.However,when the variable horizontal displacement variable axial force variable angle complex command is adopted,the error is still obvious,and the control of the horizontal displacement still needs to be improved.(4)The three-degree-of-freedom quasi-static test was performed using the control software to verify the accuracy of the force-displacement mixed control method considering the geometric nonlinearity.The test results show that: The method can make the actual reaction of the test piece track the corresponding target command well,with the smallest error and the best control effect.