Marble and heavy stone columns are widely diffused in ancient churches and historical buildings in all the Mediterranean area. Their good mechanical properties allowed carrying great load values, while their bright colours and aesthetical characteristics have been used by a lot of ancient architects to achieve structural solutions with great visual impact.
Despite their good compressive strength, marble columns could be damaged from environmental effects (e.g. long- term effects or thermal loads), which could crack the structural members. In this way, the slenderness of the column increases drastically and the presence of an imposed ground shaking could be critical, since the column will be more vulnerable to rocking motion and to overturning risk.
This paper focuses on the rocking behaviour of cracked granite and marble columns subjected to a pulse type ground shaking. The effect of the presence of circular collars is analysed by means of a mechanical model. The overturning spectra are determined including the presence of the collars, showing their efficiency in reducing the overturning risk. Comparisons are shown with numerical analyses and a simplified design method is proposed.
rocking motion
Rocking motion of a masonry rigid block under seismic actions: a new strategy based on the progressive correction of the resonance response
A new strategy of analysis is presented here for the rocking motion dynamics of a rigid and thin block with damping represented by the coefficient of restitution. This is based on the construction of the “limit” artificial accelerogram which involves an upper bound of the block response and on its subsequent correction to consider more realistic situations. The “limit” artificial accelerogram is characterized by a particular sequence of instantaneous pulses and a simplified equation of motion is adopted for the analysis. It is firstly underlined that the amplitude resonance for the block is much more intense and frequent than that for the linear elastic oscillator. A “reduced” accelerogram is then defined by means of two criteria: 1) increasing the frequency of the pulses and 2) considering the limited duration of the stronger phase of an earthquake. The results are discussed with reference to the influencing parameters such as the coefficient of restitution and the size and slenderness of the block. A numerical example shows the comparison between the results from this procedure with those obtained by the Italian seismic codes NTC08 for the limit analysis of masonry blocks.
For this paper is available an extended abstract after the text in Italian