Pseudo-dynamic Testing Method For Specimen With Large Stiffness

Pseudo-dynamic (PSD) testing is an important tool to evaluate and studyseismic performance of structures. With the development of economy andtechnology, modern engineering structures become much larger and more complexand the traditional scaled model tests cannot satisfy the needs of the scientificresearch and engineering applications any more. Therefore, large-scale evenfull-scale model tests have obtained increasingly attention in structural experimentalengineering, in which the stiffness of the test specimen is usually very large.However, owing to the limited resolution of the displacement control of the actuator,it may be difficult to impose small displacement commands on large stiffnessspecimens in displacement control, and hence reliable PSD test results are also hardto attain. Thus, it is necessary to study the PSD testing method for the large stiffnessspecimens, which is of great significance in enriching and improving the traditionalseismic test methods.This study focuses on problems of PSD testing for large stiffness specimens.Main work and finding are as follows:1. A discriminate formula defining the range of large stiffness specimens isproposed from the view point of tests, which can be used to establish a reasonabletest plan. A full-scale single-storey single-bay masonry model is fabricated tosimulate a single-layer ten-bay original structure. At first, the mechanical propertytest of the structural material is carried out. Then, the PSD test of this model underlarge earthquake excitation is performed to explore its seismic performance. Resultsshow that this kind of structures has excellent seismic behavior that greatly exceedsthe seismic precautionary criterion under the rare earthquake attack of our country.Finally, numerical simulations of the PSD test of this model are performed. Resultsshow that PSD tests of large stiffness specimens under small earthquake excitationwith displacement control is difficult to accomplish.2. In order to clearly further demonstrate difficulties in displacement control,loading tests of small displacements are carried out. A mixed displacement-forcecontrol method is presented, which brings a high-resolution sensor into thedisplacement control loop to circumvent insufficient accuracy of the loading devices.The stability and steady state error of this method with a proportional-integraldisplacement controller are analyzed, and then a practical method for designingparameters of the displacement controller is introduced. Finally, the feasibility andeffectiveness of this method for tests of large stiffness specimens is verified by numerical simulations and real experiments. Research shows that this particularapproach can well resolve problems in displacement control of large stiffnessspecimens.3. The reaction force of large stiffness specimens is usually larger even at asmall displacement response and thus force control mode is more suitable forhydraulic-servo actuators. For this reason, force control mode of actuators isproposed to incorporate to the equivalent force (EF) control method, which is a PSDmethod based on an implicit integration algorithm replacing numerical iteration withforce feedback control. The stability condition and steady state error of the outerloop with a proportion-integration EF controller are analyzed. Numericalsimulations and real experiments are performed to verify the feasibility andeffectiveness of this method. Results show that this method is superior to the EFcontrol method with displacement control of actuators.4. A force-displacement switching control method based on the positivedisplacement feedback loop is proposed in order to combine the advantages of theforce control mode and the displacement control mode and to accomplish automaticswitching in PSD. Firstly, the switching process is theoretically analyzed. Numericalsimulations and test results demonstrate that this method can provide automatic andsmooth switching between force control and displacement control, which can bewell applied to the PSD with large stiffness specimens.