UNBALANCED FORCE COMPENSATION IN SUBSTRUCTURE TESTING BASED ON ONLINE SYSTEM IDENTIFICATION

摘要

Concerning algorithms for substructure tests, there are some advanced methods that can deal effectively with interaction between experimental and numerical substructures such as analog feedback (Thewalt et al. 1987), digital feedback (Dorka et al. 1990) or predictor-corrector (Ghaboussi et al. 2005), etc. The main advantage of these methods is that accuracy of implicit schemes can be benefited. In this research, the digital feedback algorithm is used for real-time substructure test. In substructure tests with digital feedback, error of algorithm comes from integration scheme and sub step control. A suitable implicit integration scheme with proper parameters for a certain application should be used in order to ensure stability and critical accuracy. Besides the use of integration scheme, error in sub step control should be treated by choosing an adequately small value for sub step time. The error due to sub step control would theoretically approach null, if the sub step time interval approaches zero. However, a problem is that the sub step time interval cannot be too small because of large numerical effort, digital error, measuring and control limitations. The non-zero error of sub step control is an unbalanced force which should be compensated to improve the accuracy of substructure tests. This paper introduces an unbalanced force compensation method that is based on online system identification in time domain. Since the unbalanced force is very well related to the dynamic response of the system, this force can be estimated and then compensated in every step. Numerical results and tests of some example models with earthquake loads show the applicability of the compensation method. In addition, convergence and other properties of the method are also discussed.