CARACTERÍSTICAS TÉCNICO CONSTRUCTIVA .1 CAPA DE RODADURA

YELLOW TUFF MASONRY

Metrological researches carried out on Neapolitan yellow tuff masonry have identified three different constructive typologies, depending on chronology, morphology and geometric parameters:

- ‘cantieri’ masonry, widely used between the XVI and the XVII century;

- ‘bozzette’ masonry, used around the XVIII century;

- ‘blocchetti a filari’ masonry, used in the XIX century and in the first half of XX century.

A large presence of such masonry typologies in the Neapolitan area permits a deep knowledge of geometric and constructive characteristics diffused at that time. The

‘cantieri’ masonry was widely used in the Spanish Quarters, in the suburban area next to the city walls during the period of Spanish Viceré, and often used also for the construction of foundations of important buildings. Such type of masonry are made mainly with roughly cut stones by means of manual tools, joined with irregular courses of mortar. These stones are usually called ‘spacca atoni’, ‘spaccate’ or

‘spaccatelle’, depending on size and shape. After the seismic event of 1688, in the last quarter of XVII century, a new constructive technology started to develop and walls were made with ‘bozzette’ stones, vertically worked onto the external faces and roughly cut on the internal ones. Masonry was used to be built with such stones in rows of 13 cm of height (‘mezzo palmo’). Starting from the Napoleonic period,

‘blocchetti’ masonry walls were used, made with smaller blocks, easily recognizable due to different dimension ratio. Also, thinner and variable bed joints were commonly

used in this type of masonry. In past years, the authors of the present study carried out an experimental research on scaled columns 1:10 made by the same masonry typologies previously described, obtaining a non-linear σ-ε diagram from which the M-χ curve of the transversal cross-section of the panel was obtained together with the theoretical F-δ diagram. The study carried out by (Calderoni et al., 2009) [12] is an extension of previous work on real scale walls. It is important to underline that the mechanical characteristics of tuff are not subject to high deterioration with time; in fact, the wind, only in the case it insists on the material for long time, can lead to erosion of material, while the rain and the moisture only temporarily reduce the mechanical characteristics of stones. This permitted to employ stones from the original time of constructive typologies for the constructions of models, taken from old quarries already used at that time or from the rests of buildings aggregates present in the Neapolitan area.

Figure 3.21. Built panels: ‘bozzette’ (a), ‘cantieri’ (b), blocchetti (c) [12].

In order to reproduce the mortar employed for the construction of the elements and to know the mix, the type of binder and aggregates used at that time, some documents from literature were analysed and some physical and chemical tests were carried out. In Figure 3.21 it is reported a picture for the panels build according different typology, while in Table 3.15 the dimensions of every panel are summarized.

Table 3.15. Components and dimensional characteristics of panels [12].

The experimental campaign concerned a first part for the characterization tests on tuff specimens and mortar specimens. In particular, the UNI EN 771-6 for tuff specimens, and the UNI EN 1015-11 for mortar specimens were followed for test execution. In Table 3.16 are summarized the values of mechanical characteristics of masonry components.

Table 3.16. Mechanical characteristics of masonry components [12].

During compressive tests on whole masonry panels, in order to avoid the possibility of localized rupture of masonry or eccentric loads, on top of panels was applied a self-levelling mortar in contact with a steel profile through which the load was applied. Between the steel profile and the hydraulic jack a spherical hinge was placed. Deformation were read by means of LVDT. In total, six real scale panels were

tested according to the following procedure: a first phase where a 0.1 N/mm² load was applied in order to let the specimen settle; a second phase where a 0.5 mm/s displacement was imposed with breaks of 10 seconds.

The tests give load – displacements diagrams from which σ – ε curves were obtained. In Figure 3.22 the results are reported for the ‘bozzette’ walls.

Figure 3.22. Compressive tests results for ‘bozzette’ walls [12].

During the loading process, the first damage was attained when the peak strength was reached, and a vertical crack appeared. Afterwards, there was the formation of further cracking surfaces, inclined by an angle of 45°, demonstrating a good bond between tuff and mortar. The maximum strength was reached for an interval between 2.55 N/mm² and 4.34 N/mm², corresponding to a strain ranging from 0.4% to 0.8%. The interval related to the ultimate strain goes from 3.2% to 5%. The diagram shows a first elastic behaviour, with a curve starting to bend right after the strength was reached, followed by a softening branch till the ultimate strain was reached, showing a good plastic capacity.

Moreover, a comparison in terms of ultimate strength was done, between the tested models and the formulation given by the Eurocode 6. The results are reported in Table 3.17, showing that the code underestimate the strength since it is calibrated in modern constructive typologies, resulting in a not so good formulation for prediction of strength of ancient masonry walls.

Table 3.17. Mechanical characteristics of masonry components [12].

In the behaviour of different masonry typologies some differences can be found due to the employed mortar and to the arrangement of the blocks. The low peak strength of the ‘bozzette’ wall and the ‘blocchetti’ wall is due to the low quality of mortar, in the first case, and to the low mechanical capacity of tuff used in the second case. For the behaviour of the softening branch, very important is the bond behaviour between mortar and blocks and the interlocking created by the mutual arrangement of both elements. Finally, the historic masonry showed a very good behaviour in compression and good plastic capacity, which seems to be due both to the blocks arrangement and to the mortar type.