The response of a two-degree-of-freedom dynamic sliding system subjected to uni-directional horizontal dynamic and seismic excitations

Abstract

An investigation is presented that studies the response of a two-degree-of-freedom dynamic sliding system; that is a single-degree-of-freedom oscillator being fi xed on top of a rigid block that can slide on its supporting shaking table along a horizontal axis when subjected to unidirectional dynamic or earthquake excitations along this horizontal axis. This problem appears to be of interest in predicting the dynamic and earthquake response of superstructures supported on a large foundation block capable of horizontal sliding by means of seismic sliding isolators. Special mock-ups are tested at the shaking table of Aristotle University for this purpose utilizing horizontal simulated earthquake excitations based on prototype earthquake ground motion recordings. The numerical results, which were obtained by a computer software developed for this purpose, are compared with the corresponding experimental measurements. The measured acceleration and displacement responses of the mock-ups appear to be, in all the examined cases, in reasonably good agreement with the numerical predictions. However, in certain cases, the numerically predicted sliding displacement of the rigid block appears to have an offset that differs from the sliding response that was observed during the experiments. This is more pronounced when there is no spring linking the rigid block with the shaking table and must be attributed to manufacturing tolerances of the mock-ups. It is demonstrated that the developed software, although it tries to represent such a rather complex problem in a simplifi ed manner, can be useful at the preliminary design stage of structural systems resting on sliding isolators. Results from various experimental and numerical tests demonstrate that the oscillator's response is generally made smaller by the sliding of the rigid block. This is true for a wide range of frequencies; however, there is a relatively narrow frequency window in which the oscillator's response is amplifi ed. This frequency window has a peak value that is slightly higher than the oscillator's eigen-frequency when it is considered to be a single-degree-offreedom system fi xed at its base.

The Dynamic Response of a Vertical Dry-Stone Masonry Assembly as a Mock-Up of Masonry Wall Fortifications

“…9b. As can be seen in this figure, the top 5th-stone develops a peak acceleration of approximately 0.68 g. It was observed in the past during the experimental sequences with columns having drums that for a given frequency of excitation there is a boundary between the stable rocking response and the overturning (Manos et al 1990(Manos et al , 1996(Manos et al , 1997(Manos et al , 1999(Manos et al , 2000(Manos et al , 2001(Manos et al , 2002(Manos et al , 2011(Manos et al , 2013(Manos et al 2015. This boundary has relatively high values of non-dimensional excitation amplitude for high frequency values and relatively low values of non-dimensional excitation amplitude for low frequency values (Manos et al 2015).…”

“…The columns and the dry stone masonry are connected at the top with the epistyle (entablature), also composed of monolithic orthogonal blocks, spanning the distance the columns and the stone masonry wall. The earthquake response of free standing columns has been researched by the first author (Manos et al 1990(Manos et al , 1996(Manos et al , 1997(Manos et al , 1999(Manos et al , 2000(Manos et al , 2001(Manos et al , 2002(Manos et al , 2011(Manos et al , 2013(Manos et al , 2015 in the past as well as by other researchers (Abrazeys et al 2011Aslam et al 1978, Demosthenous 1994, Koh et al Koh and Mustafa 1990, Papantonopoulos et al Papantonopulos et al 2002, Psycharis et al 1993, 1990, 2003, and Spanos et al 1984. This paper focuses on the response of square monoliths that lie on top of each other without connecting mortar at their contact horizontal surfaces, as it is typical in the mentioned before dry stone masonry construction.…”

Limit-State Response of Stone Masonry Used in the Construction of Cultural Heritage in Greece

“…From this measurements the friction coefficient was found to be equal to μ=0.72. Information on the sliding response can be found in [15] to [21].…”

“…The lower drum is rigidly attached to the base-moving platform, so that it can be subjected to the desired base motion of the shaking table, which can also be one-direction horizontal component of a given earthquake recording. The equations of motion were used to create software capable of predicting numerically the sliding response ( [20] and [21]). This software was validated by applying it to numerous measurements obtained from the experimental arrangement depicted in figure 4a.…”