Revised Seismic Intensity Parameters for Middle-Field Horizontal and Rocking Strong Ground Motions

This paper presents a new method for determining rocking ground motion considering the effects of both time delay and loss of coherency in spatially variable seismic ground motions. Acceleration, velocity, and displacement response spectra resulting from the rocking component are also derived. Next, new seismic intensity parameters are proposed to estimate the combined action of the middle-field horizontal and rocking motions on the earthquake excitation of structures. These seismic intensity parameters are revised forms of the widely used ones for characterizing translational components, namely, peak ground velocity, peak ground displacement, cumulative absolute displacement, acceleration response spectrum, acceleration spectrum intensity, Fajfar intensity, and Kappos spectrum intensity. In addition, an expression for the estimation of the effect of the base tilt due to the rocking ground motion on the structural response is presented. The main advantage of the proposed relations is that they can be easily used to evaluate the approximate effect of the rocking component on the seismic excitation of structures.