The Riding School in the Royal Palace of Naples: Transformations ...

Figure 12. Bending moments diagram for the calculation scheme of fig.9
In fact, the insertion of the lateral trestles has shown to be detrimental: their absence would affect
not much the distribution of bending moments, which would remain of about the same size, but the
values of the normal stresses, which would enlarge enormously, quadruplicating on the tie-beam
and the collar-beam. Obviously, the presence of the trestles induces a strong thrust on lateral
masonry walls, but not so large as to give rise to overturning phenomena. The loads resultant stay
inside the leaning base of the wall, giving a maximum compressive stress in masonry of about 0.9
MPa.
Structural interpretation of the behaviour of the centrings
In Niccolini’s estimative metrical evaluation, when speaking about the false vault of the riding
school, he said: “Description of the 52 poplar centrings, put under the tie-beams of the trusses to
more strengthen them”. From these words it seems that perhaps Niccolini thought that the centrings
did not just perform the simple function of making the ceiling, but also provided a structural
contribution to the main structure. So a calculation has been done inserting the false vault with its
poplar centrings between the bearing structural elements of the truss. Results are those shown by the
normal stresses diagram (fig.13) and bending moments diagram (fig.14) quoted below, from which
a reduction of the stresses on the tie-beam is evident. However this solution, if admissible, would
produce a considerable increase of the thrusts on the masonry walls, apparently sufficient to
overturn them, and consequently it can be concluded that this scheme is not a description of the real
behaviour of the structure built by Niccolini. Moreover, from the description given in the document
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