DETERMINATION OF STORY STIFFNESS OF 3-DIMENSIONAL FRAME BUILDINGS

Few past system identification studies have attempted structural model s with many degrees-of-freedom (DOFs) owing to the numerical difficult y with regard to convergence and computational speed. Even fewer studi es have considered a three-dimensional building with the torsional res ponse taken into consideration. in this respect, an 'improved condensa tion' method for the system identification of multistorey three-dimens ional frame buildings is developed. Specifically, reductions in storey stiffnesses are determined for the quantification of structural damag e or deterioration in each storey of a building. Both static and kinem atic condensations are employed to reduce the DOFs of a (complete) mat hematical model for the building, resulting in a condensed model of mu ch fewer DOFs. The modelling error is minimized by introducing a remed ial model whose parameters are identified by using the extended Kalman filtering technique. A stiffness correction factor is computed to suc cessively update the complete model. Finally the method yields integri ty indices to quantify changes in the respective storey stiffnesses. A numerical simulation example of an asymmetric three-storey frame buil ding which has a total of 270 DOFs is presented. Three cases of differ ent damage status of the building are considered. The proposed method is implemented to identify the storey damages, under the influence of input and output noise. The numerical results show that this method ac curately reports the extent of stiffness reduction at each storey of t he building and is computationally efficient because of a smaller syst em used for identification in the remedial model.