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Proceedings of the International Conference on
Advances and New Challenges in Earthquake
Engineering Research, Hong Kong Volume
SIMULTANEOUS ESTIMATION OF STRUCTURAL PARAMETER
AND EARTHQUAKE EXCITATION FROM MEASURED
STRUCTURAL RESPONSE
J.Chen 1 - 2 , J.Li 2 and Y. L. Xu 1
'Department of Civil and Structural Engineering, The Hong Kong Polytechnic University
Hung Horn, Kowloon, Hong Kong, China
Department of Building Engineering, College of Civil Engineering, Tongji University
Shanghai 200092, China
ABSTRACT
This paper presents an element level system identification method in the time domain to
simultaneously estimate structural parameters and earthquake-induced ground motion from measured
structural responses only. The method, named the dynamic compound inverse method, combines the
least-squares technique and the statistical average method together, leading to a proper iterative
procedure for a better solution of the problem. The earthquake-induced ground motion is first
conjectured using the measured structural responses and the assumed initial values of the structural
parameters to be identified. The conjectured ground motion is then forced to comply with the
dynamics of the given structure using the statistical average method. The modified ground motion is
further used to provide a new estimation of the structural parameters using the least-squares technique.
Repeating the iterative procedure until a preset convergence criterion is reached then provides the
simultaneous estimation of structural parameters and earthquake excitation. Numerical example using
a shear building is carried out to demonstrate the feasibility of the dynamic compound inverse method.
The results show that the method can estimate the structural parameters and the ground motion
satisfactorily for the cases that the structural responses are not polluted or slightly contaminated by
noise.
INTRODUCTION
The frequency-domain modal approach is commonly used to identify natural frequencies, modal
damping ratios, and mode shapes of a structure from measured structural responses without requiring
the information on external excitation but assuming the external excitation to be a white noise random
process. Though the natural frequencies and mode shapes are representative of the stiffness of a
structure to some extent, it may not be possible to use the identified natural frequencies and mode
shapes to quantify even a severe level of structural damage because they are not sensitive to the
damage of individual structural members. Furthermore, earthquake-induced ground motion cannot be