Earthquake performance of buildings (CAMUS project) I - Discretization of the structure and numerical modelling of linear response

This paper presents the CAMUS project (Conception et Analyse de MUrs sous Séismes, 1997-1998) with reference to the LCPC's entry to the forecasting competition associated with this programme (digital modelling of the seismic response of a building). The experimental model of the building was tested on a vibrating table at the CEA in order to conduct an experimental analysis of its seismic response. This first part of the study deals with the modelling of the dynamic linear response of the structure (using CÉSAR-LCPC) and analysis of the way the characteristics of the model influence the modal parameters. Analysis of the intrinsic modes of vibration of the structure alone does not give the natural frequencies determined by experiment. Two comprehensive models (one two-dimensional, the other three-dimensional) were then used to analyze the structure/vibrating table combination. The natural frequencies they output were lower and nearer to the observed frequencies. We were then able to detect the intrinsic vertical mode of vibration, caused by the flexibility of the table supports. The dynamic linear response was determined using a modal superimposition technique and the contribution of each mode of vibration was analyzed (effective masses). Part two of the paper will provide an account of the nonlinear dynamic analysis and the comparison with experimental results.