Nonlinear seismic torsional pounding between an asymmetric tower and a barrier

Seismic torsional pounding between an asymmetric single-story tower and a neighboring barrier under harmonic ground excitation is modeled as the nonlinear Hertz contact in this paper. The governing equations of motion are numerically solved using the fourth-order Runge-Kutta method with an adaptive step size control. An analytical solution is obtained for the first time for a special case of periodic torsional pounding. Results of our numerical simulations reveal that torsional pounding tends to be much more complex and unpredictable than translational pounding, and most of them are either multiple or chaotic impacts. The maximum torsional impact velocity tends to be insensitive to the changes of separation distance and eccentricity as long as impact is developed. Although the analytical solution fails to predict the exact impact velocity of multiple torsional pounding, it does provide some useful insights into this complex phenomenon. The analytical solution succeeds in predicting the overall patterns as well as the abrupt jump of torsional impact velocity spectra.