PSI - Issue 44

Mariateresa Guadagnuolo et al. / Procedia Structural Integrity 44 (2023) 766–773 Guadagnuolo et al. / Structural Integrity Procedia 00 (2022) 000–000

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The procedure outlined above can be used to generalize some results and analyze the behavior of chimneys as the height of both the under-roofed and protruding parts varies. Many royal palaces are indeed characterized by the presence of large and high attic floors crossed by the flues of the chimneys below, according to a construction technique widely used in recent centuries. For this purpose, both the height H roof of the flue portion under the roof and the height H out of the protruding portion were varied. Figure 6 shows the indices ζ E obtained by varying H roof and H out between 1 m and 3 m. The ground acceleration of the site of the Carditello Royal Palace was used since it is representative of low seismicity areas, where many royal palaces are located. Figure 6 shows that the attic floor height H roof plays a decisive role in the seismic capacity of the chimney (significant change in the indices ζ E ) only when the height H out of the protruding part of the chimney stack is equal to or less than about 1.5 m.

3,00

H out =1.5 m H out =1.0 m H out =2.0 m H out =2.5 m H out =3.0 m

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Index ζ e

1,50

1,00

0,50

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Height H roof [m] 0,0 0,5 1,0 1,5 2,0 2,5 3,0 3,5 4,0 4,5 5,0

Fig. 6. Influence of H roof and H out on the seismic capacity of chimney stacks

4. Conclusion The paper is aimed at contributing to the safety and conservation of historic chimney stacks, non-structural elements often neglected. To this end, a procedure to study the overturning failure mechanisms of masonry chimneys is presented. It is a revised version of the customary kinematic procedure used for the vertical bending failure mechanisms of masonry walls: it considers both the actual position of the translation constraint due to the roof structure and the upper protruding part of the chimney. The outcomes obtained applying the procedure to the chimneys of the Royal Palace of Carditello are representative of the seismic behavior of many chimney stacks. They confirm that historic chimneys, usually characterized by a great height of the protruding stack, are particularly seismically vulnerable because they can collapse at rather low values of the peak ground acceleration. Values of about 0.05 g were computed through the static force-based approach (linear kinematic procedure) as the threshold for activating the overturning mechanism in chimneys of buildings with geometric characteristics similar to those of the Royal Palace of Carditello. The displacement-based approach (nonlinear kinematic procedure) provided large collapse ground accelerations (of about 0.15 g). This value should be considered more consistent since considers the possible reserve capacity of dynamic rocking phenomena. The paper also confirms that the seismic capacity of historic chimney stacks depends on the height of the attic floor when is similar to the height of the protruding part or when the latter is very small. This also reduces the role of the roof structure, which is decisive only when it has high strength (e.g. r/c structures), and the overturning of only the stack is prevented. Acknowledgments The “Real Sito di Carditello Foundation” and its President, Prof. Luigi Nicolais, are gratefully acknowledged.