Pseudo-Dynamic Testing Method For MDOF Structures

The pseudo-dynamic test (also referred to as the on-line computer controlled test) is an experimental technique for simulating the seismic response of structures and the structural components with respect to the time domain. In this technique, the dynamic response of a non-line structure in each step is computed by adopting a step-by-step integration procedure to solve equations of motion. Then the restoring forces developed by the structure are measured experimentally and physically imposed on a test specimen. It is believed that pseudo-dynamic test methods can provide more accurate results because of using measured restoring forces instead of the mathematical description of the non-liner model which is very hard to predict accurately.The center different method, double β parameters method (explicit) and a -C method (implicit) are introduced in this article. The computation algorithm used by these three integration method are programmed for simulating the dynamic responses of the given models. The period distortion effected by the integration time interval is studied. The results show that a -C algorithm based on Newton iteration can eliminated the spurious higher-frequency vibration signal arose by experimental errors. With the stimulation procedure, more suitable integration time interval can be checked before testing. For big stiffness structures, unreasonable result will be obtained due to its characters and the system errors, so it can be concluded that the pseudo-dynamic test is not suitable for the big stiffness structures.The step-by-step loading method is proposed based on the current servosystem. The target displacement signal can be generated without being interrupted by the computation of equations of motion, extrapolation and interpolation procedures using a Lagrange polynomial for accurate displacement are explicated. "Response Analysis Task" and "Signal Generation Task" are separated run for saving the memory of the controller. The hardware constituents and software functions and modules of the testing system with MDOF are designed. For the conventional purpose, the computed procedures are programmed as sub-function which is independent with the main control procedure and can be easily altered by other calculated functions.