Rotational Components of Strong-Motion Earthquakes

Abstract eng:
The rotational components associated with the dynamic response of elastic and of poro-elastic half space can be as important as the actual deformations, for computation of the response of the half space and for the response analyses of engineering structures, and must be included in all analyses. The basic theory of elasticity shows that the Euclerian strain tensor of deformations is expressible in terms of the linear strain tensor and the second order terms of rotation tensor. At present, all structural analyses already deal with the generalized displacement of the 3 components of translations and the 3 components of rotations as the 6 independent components. These six generalized components are often simultaneously estimated using the kinematic equations of forces and moments Since rotations are defined in terms of derivatives of translations, with respect to space coordinates, there always should exist analytic expressions for rotations in terms of the translations. This is certainly the case when the translation components are given in rectangular coordinates. Using surface waves, the method of Trifunac (1971) for generating artificial, synthetic strong motion accelerograms can thus immediately be extended to generate both synthetic torsional and rocking accelerograms and of their response spectra (Lee and Trifunac, 1985, 1987, 2008). Those are constructed from the horizontal and vertical acceleration components. These rotational components of strong ground motions are gaining attention as it is becoming evident that they can contribute significantly to the overall response of structures during strong earthquake motions. This paper intends to stress the importance of the rotational components of accelerograms, to develop theories and algorithms for generating rotational motions from the corresponding available translational motions, and to check such validity from several actual, real rotational recordings.

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