Department of civil and environmental engineering

In this article a comparison between two non-linear finite element approaches for the numerical estimation of the ultimate failure load of masonry arches is presented. According to the first model, the geometry of the arch is divided into a number of unilateral contact interfaces which simulate potential cracks. Opening or sliding for some of the interfaces indicates crack initiation. The second model uses two-dimensional finite elements for the simulation of the arch. When tensile stresses appear, upon an adaptive stepwise procedure, the corresponding elements are replaced by unilateral contact elements which represent cracks. In both models the fill over the arch, that could strongly affect the collapse behaviour increasing the bridge load carrying capacity, is taken into account. Moreover, the ultimate load and the collapse mechanism have been calculated by using a path-following (load incrementation) technique. Both models are developed and applied on a real scale masonry arch; results are comparable with both the experimental collapse mechanism and the ultimate load failure. To cite this article: M. Betti et al., C. R. Mecanique 336 (2008).

In this paper a Romanesque masonry church is analysed in order to assess its structural behaviour and its seismic vulnerability with respect to the actual state of conservation. Starting from a specific case study, a contribution to the issue of modelling and analysis of monumental masonry buildings under seismic action is provided. A finite element methodology for the static and dynamic nonlinear analysis of historical masonry structures is described and applied to the case study. A quasi-static approach (the seismic coefficient method) for the evaluation of the seismic loads has been used (as indeed is common in many analyses of the seismic behaviour of masonry structures). The comparison demand vs. capacity confirms the susceptibility of this type of building to extensive damage and possibly to collapse, as frequently observed. Moreover the actual efficiency of current techniques for repairing and strengthening are analyzed in order to evaluate their benefits. The analysis of repairing and strengthening techniques show the effectiveness of the usual structural reinforcement in terms of increased seismic capacity. The paper advocates that significant information can be obtained from advanced numerical analysis, namely with respect to the understanding of existing damage and to the minimum and adequate design of strengthening. A clear understanding of the structural behaviour and reliable strengthening, based on sophisticated tools of structural analysis, can therefore reduce the extent of the remedial measures in the restoration of ancient structures.

The paper presents a synergic and multidisciplinary approach where laser scanner survey, radar interferometric monitoring and finite element (FE) numerical modelling are used for expeditious and no-contact dynamic identification of monumental masonry towers. The methodology is applied to a real case of great historical interest: the "Torre del Mangia" (Mangia's tower) in Siena (Italy). The tower geometry was acquired through Terrestrial Laser Scanning (TLS) techniques. The tower oscillations were detected using an interferometric radar in "Piazza del Campo", the square facing the Mangia's Tower, along three alignments, and movement of the structure at several heights were recorded. A FE model, built on the basis of the geometry acquired through the TLS, was used to interpret and verify the physical meaning of the experimental results. Through the discussion of the case study, the paper shows that the proposed approach can be considered as an effective and expeditious method for assessing the dynamic behavior of monumental buildings (and to plan interventions) on territorial scale.

Many ancient masonry towers represent one of the most relevant characteristics of both the Italian and the whole European territory. To preserve their cultural and economic value, they often call for a deeper investigation to assess their state of conservation. This paper offers a contribution to the issue of monitoring and analysis of monumental masonry tower, by discussing an experimental investigation survey made on an illustrative masonry tower: the Italian Medieval ''Torre Grossa'' (Big Tower) of San Gimignano in Toscana (Italy). The tower is part of the UNESCO cultural heritage after 1990 together with the city centre; it dates back to the thirteenth century and its height is about 55 m (one of the tallest masonry tower in Italy) with a square cross-section whose side is about 9.5 m. During the experimental campaign, both static and dynamic tests were performed. Static tests (flat-jack and laboratory test on cored specimens) were used to estimate the mechanical properties and the ultimate strength of masonry. Dynamic tests led to the measurements of the natural frequencies and corresponding modal shapes of the whole monument. By using the finite element technique, a 3D model of the tower was built (macro-modelling) and it was calibrated on the basis of the in situ investigation survey; the degree of restrain offered by the neighbouring buildings was estimated by tuning the numerical results with those obtained from the dynamic tests. The paper, by discussing the design and results of the experimental campaign, aims at offering a contribution to both the investigation and the structural behaviour of historic masonry towers providing useful hints to deepen the knowledge on their structural behaviour.

This paper discusses the cracking pattern in a historical Italian palace proposing a diagnosis for the origin of the actual damage state. The analyzed building, which dates back to the seventeenth century, is a masonry building with a rectangular plan section located in Piancastagnaio (South Tuscany, Italy). The building exhibits a severe and variegated vertical and horizontal cracking pattern mainly affecting the southern and eastern façades. Due to the damage, the palace was evacuated by the Public Authorities during the 1980s and a series of provisional remedies (mainly steel chains) was added. Through the use of the finite element technique, the paper provides an interpretation of the manifested damage. The aim of the diagnosis, supported by the numerical results, is to design an extensive in-situ investigation on the palace. Moreover, the paper aims at evaluating the effectiveness of the actual temporary retrofitting (mainly steel chains) used to freeze the present damage. At the end of the paper the in-situ investigation is presented and discussed.

A microwave interferometer has been employed to remotely detect the oscillations induced by vehicular traffic on the dome of the Baptistery of S. Giovanni in Firenze (Italy). The measurement has been carried out to assess the structure oscillations reduction after the ordinance issued by the Major of Florence forbidding all kind of vehicular traffic in the square around the Baptistery starting from October 25, 2009. A simplified preliminary finite element model of the structure, using average literature mechanical parameters, has been used to determine the best instrument installation position and the structure area to be surveyed. Subsequently, the dome oscillations have been recorded for two consecutive weeks starting one week before the traffic block. A spectral analysis on the acquired data has been then performed and a more complex FEM model has been built to interpret the physical meaning of the acquired data. The material mechanical parameters have been finely tuned to reproduce the lowest spectral component found which was very close to the main mode oscillation frequency predicted by the simplified model. The obtained values of mechanical parameters are reasonable for the monument materials and slightly different from average. Measurement results indicate that the traffic block caused a reduction of the daytime maximum oscillations power of around 50÷60% and a decrease by approximately 33% has been observed in the peak component particle velocity. The residual measured oscillations are attributable to human activities around the square.

The paper offers a contribution to the issue of modelling and analysis of architectural heritage through the discussion of an illustrative case study: the Italian Medieval Castle of San Niccolò (Toscana, Italy). In the past the castle exhibited a wide damage, and to prevent its ruination, restoration works were executed in the eighties of the last century. Using the finite element technique, a 3D numerical model of the castle has been built that has been used to identify the main sources of the damages and assess the effectiveness of the restoration works. The paper shows that advanced numerical analyses could offer significant information both for the understanding of the causes of existing damage and the minimum and adequate design of strengthening. The understanding of the structural behaviour can indeed reduce the extent of the remedial measures, offering efficient strengthening tools.