Seismic Reassessment of the Leaning Tower of Pisa: Dynamic Monitoring, Site Response, and SSI

Abstract

The Tower of Pisa survived several strong earthquakes undamaged over the last 650 years, despite its leaning and limited strength and ductility. No credible explanation for its remarkable seismic performance exists to date. A reassessment of this unique case history in light of new seismological, geological, structural, and geotechnical information is reported, aiming to address this question. The following topics are discussed: (1) dynamic structural identification based on recorded earthquake data; (2) geophysical site characterization using a two-dimensional array; (3) seismic hazard and site response analysis considering horizontal and vertical motions; and (4) soil-structure interaction (SSI) analysis calibrated using lab and field data. A substantial shift in natural period, from about 0.35 s to over 1 s (a threefold increase, the largest known for a building of that height) caused by SSI, a wave parameter (1/ σ) of about 0.3, and a minor effect of vertical ground motion are identified and may explain the lack of earthquake damage on the Tower. Recommendations for future research, including the need to establish a seismic bedrock deeper than 500 m, are provided.

Geotechnical Characterization for Territorial Planning of a Special Economic Zone at a University Campus in Ecuador

“…These considerations must always be adequately considered in territorial planning processes; otherwise, structures could be affected by seismic activity, settlements, or landslides [67,68]. Some notable cases of this problem were the leaning of the Tower of Pisa, the rockslide of the Vajont dam, and the collapse of a group of silos in Canada in 2016 [69,70].…”

A Novel Fe Model for the Tower of Pisa

“…To avoid an excessive simplification of the Tower's base restraint, a portion of soil under the structure has also been modelled (Figure 3c). In the present state of things, it is made up of four layers, corresponding to the three Complexes, the most superficial of which (Complex A) is again split according to the experimentally determined properties [1].…”

“…The masonry foundations of 19.6 m in diameter rest on weak, highly compressible soils, which can be grouped in three complexes having different mechanical characteristics. Complex A, ranging to a depth of 10 m, is the most compressible layer, made of silts, clays and sands, with a water table between 1 m and 2 m deep; Complex B consists of very soft sensitive marine clays up to a depth of 40 m; Complex C is a dense sand layer extending to considerable depth [1].…”

Ambient Vibration as a Basis for Determining the Structural Behaviour of Watchtowers against Horizontal Loads in Southeast Spain

“…Besides, the method avoids the use of any type of stress on a structure that may be in poor condition, thus, eliminating a risk both for the people performing the test and for the structure itself. The outcome of various experiments [32][33][34][35] reveals that the use of ambient vibration is sufficiently precise to obtain the fundamental period of a structure and other dynamic characteristics.…”