Development of innovative control system for hybrid testing of stiff structures under seismic excitation

TitleDevelopment of innovative control system for hybrid testing of stiff structures under seismic excitation
Publication TypeThesis
Year of Publication2012
Palios X
Thesis TypePhD

Hybrid simulation of stiff structures encounters significant difficulties when relying on the displacement control of hydraulic actuators. The reason being that in hybrid tests the restoring force in each step is used to calculate the displacement of the next step; therefore a potential error in the calculation (intrinsic in the case of stiff structures) has a cumulative effect, leading to results of questionable validity. Furthermore, in many cases interaction between actuators hinders the execution of tests of stiff structures. A solution to this problem encountered when testing stiff structures may be given if tests are conducted in force control rather than displacement control. This, however, presupposes that the forces to be applied by actuators in each step are known beforehand. Dominant approaches in terms of calculating forces in each step are either based on the secant stiffness matrix, or on iterations. The present doctoral thesis introduces an innovative approach which bypasses the secant stiffness matrix calculation. Two PID controllers are used (instead of one, which is the standard practice) in order to control each actuator. The first controller converts the target displacement to target force, whilst the second one controls the actuator based on the force calculated by the first controller. Moreover, when combining this strategy (dual type control strategy) with the continuous pseudodynamic method, iterations that may lead to unwanted loading-unloading cycles are avoided. The validity of the proposed strategy was assessed by conducting hybrid tests on a large-scale stiff reinforced concrete specimen. The same specimen was also used to assess the application of the strategy to cyclic tests. Lastly, the telepresence system of the Structures Laboratory is presented, which upgrades the test control system and at the same time contributes to the quality of testing and to the distribution of results to the scientific community.

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