Numerical and experimental analysis of the leaning Tower of Pisa under earthquake

Abstract

Twenty years have passed from the most recent studies about the dynamic behavior of the leaning Tower of Pisa. Significant changes have occurred in the meantime, the most important ones concerning the soil-structure interaction. From 1999 to 2001, the foundation of the monument was consolidated through under-excavation, and the "Catino" at the basement was rigidly connected to the foundation. Moreover, in light of the recent advances in the field of earthquake engineering, past studies about the Tower must be revised. Therefore, the present research aims at providing new data and results about the structural response of the Tower under earthquake. As regards the experimental assessment of the Tower, the dynamic response of the structure recorded during some earthquakes has been analyzed in the time- and frequency-domain. An Array 2D test has been performed in the Square of Miracles to identify a soil profile suitable for site response analyses, thus allowing the definition of the free-field seismic inputs at the base of the Tower. On the other hand, a synthetic evaluation of the seismic input in terms of response spectra has been done by means of a hybrid approach that combines Probabilistic and Deterministic Seismic Hazard Assessment methods. Furthermore, natural accelerograms have been selected and scaled properly. A finite element model that takes into account the inclination of the structure has been elaborated, and it has been updated taking into account the available experimental results. Finally, current numerical and experimental efforts for enhancing the seismic characterization of the Tower have been illustrated

One-Dimensional Nonlinear Seismic Response Analysis Using Strength-Controlled Constitutive Models: The Case of the Leaning Tower of Pisa’s Subsoil

“…The bedrock (i.e., Vs ≥ 800 m/s) is presumed to be very deep and some attempts have been made to increase the knowledge of the subsoil below 65 m depth. An array 2D test has been exploited to obtain the shear wave velocity profile down to more than one hundred meters from ground surface [6]. Figure 5 shows the shear velocity profile down to a depth of 100 m. The array 2D test revealed the presence of a stiffer layer (i.e., Vs ≈ 500 m/s) at a depth of about 100 m. Another methodology to investigate about the seismic bedrock depth by using the available H/V ratios is described in [14,15], however further studies and investigations have been planned in order to improve the knowledge of subsoil below 100 m depth.…”

“…The thickness and unit weight for each lithotype were assumed on the basis of the data reported in [11]. The assumed shear wave velocity profile is also based on the outcomes of the 2D seismic array test [6]. However, this profile satisfactorily matches the Vs values measured by other geophysical tests in the upper part.…”

“…The shear wave velocity profile has been recently extended down to more than 100 m below the ground level [6]. One-dimensional SRA were carried out by means of three computer codes: STRATA [28], DEEPSOIL [29] and ONDA [32,33].…”

“…During the last 20 years, several low-intensity earthquakes have been recorded. Although few events and very slight damage related to earthquakes has been observed from the construction of the monument, there is a considerable interest in the seismic behavior of the tower [4][5][6][7] triggered by the availability of new data and technologies. Within the chain starting from seismogenic zones and up to the tower, the dynamic response of its subsoil holds a crucial importance, particularly in terms of the frequency content of seismic input.…”

“…Figures 6 and 7 depict the time histories of the scaled accelerograms for an RP of 130 and 500 years, respectively, as well as the scale factor used to obtain the final accelerograms. On the basis of past studies [6], the target response spectrum was defined for two return periods (RPs) of the seismic action, namely RP = 130 years (moderate earthquake) and RP = 500 years (severe earthquake). First, the disaggregation of the seismic hazard was performed, thus providing a scenario earthquake for each return period.…”