Keywords: discrete element method, ancient columns, earthquake, object oriented programming.

The seismic behaviour of ancient monumental structures with monolithic or multi-drum classical columns and colonnade systems in two rows is investigated. In particular, the discrete element method (DEM) is utilized in the study of ancient columns subject to strong ground excitations, by simulating the individual rock blocks as distinct bodies. A specialized software application is developed, using a modern object-oriented programming language, in order to enable the effective simulation of multi-drum columns and colonnades subject to harmonic and earthquake excitations. The results obtained using the software developed are compared with results from analytical equations of motion of rigid blocks, so as to validate the software.

A large number of parametric studies have been performed in order to investigate the effect of excitation characteristics as well as the influence of geometrical and mechanical characteristics of multi-drum columns on their behaviour and response under harmonic and earthquake excitations. Furthermore, colonnade systems with epistyles, as well as, with two rows of columns, one over the other, are examined for earthquake ground motions.

Parametric studies have been performed by varying the excitation frequency and acceleration, as well as the friction coefficient and the geometric characteristics of the simulated columns and colonnades in order to assess the influence of these parameters in the seismic response of the structure.

The analysis results indicate that the frequency and the peak ground acceleration of the excitation, significantly affect the seismic response of multi-drum columns and colonnades in two rows. In particular, for low frequency harmonic excitations, the exhibited response is dominated by rocking, while sliding prevails in cases of harmonic excitations with very high frequencies. In between the two extremes, the response contains both rocking and sliding phenomena. Furthermore, the results indicate that the required acceleration to initiate rocking or sliding decreases as the excitation frequency increases. The acceleration that is required to overturn the column also increases as the frequency increases.

By examining the stability of multi-drum columns and colonnades for earthquakes that were selected from regions, where these monuments are often built, such as the Eastern Mediterranean regions, the simulations reveal that the columns have the capacity to successfully withstand strong earthquakes. The required acceleration to overturn a column decreases as the predominant frequency of the earthquake decreases.

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