PSI - Issue 11

P. Bamonte et al. / Procedia Structural Integrity 11 (2018) 322–330 P. Bamonte and A. Taliercio/ Structural Integrity Procedia 00 (2018) 000–000

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and smoke to the external environment. Chimneys were also used to disperse pollutants at higher altitudes, and reduce their impact on the immediate surroundings. After having lost their primary function, most chimneys became non-operational during the second half of the 20th century, and dismantled in several instances. In recent decades, they are regaining importance basically because of their historical and architectural value, as they constitute characteristic landmarks of the urban skyline. Initially, chimneys were low-rise and built with ordinary brickwork. From the mid-nineteenth century, the first double-wall chimneys were built, with the purpose of increasing their thermal resistance. The shape of the cross section and the dimensions of the chimney were chosen according to the type and the amount of fumes to be expelled. Guidelines concerning the construction of chimneys were already available at the beginning of the 20th century: interested readers are referred to the literature cited in Pallarés et al. (2011). Unlike ancient masonry chimneys, modern chimneys are mostly made of concrete or steel. Brickwork allowed different shapes to be obtained without using any special machinery. Constructions combining practical and architectural functions were achieved, and chimneys spontaneously became peculiar symbols of industrial plants. Whereas the building technique has changed over time, most chimneys share the typical division into three parts: base, shaft, and crown. The base is the lower part of the chimney, and has the main function of spreading stresses within the ground. It can be square, octagonal, or circular. It is usually provided with an access point for inspection. The shaft is usually conical, and performs the main function of chimneys, by conveying combustion-produced hot fumes to the atmosphere. Tapering ranges between 2 and 2.5%. The crown constitutes the upper part of the chimney, and protects it from water infiltration; it may also serve as an embellishment. Only a part of the vast number of chimneys built during the second industrial revolution still exists. Those that have not been demolished usually exhibit structural problems that require restoration interventions. The choice of the most appropriate repair technique must be based on the knowledge of the origin of the faults. In this perspective, the study of both existing and collapsed structures is of great interest. According to the survey of the faults detected on a vast number of Spanish chimneys, López-Patiño et al. (2017) identified four main sources of damage, namely changes in the construction materials, repeated actions (including wind and thermal variations), extraordinary events (including earthquakes and lightning), and living organisms. Many masonry chimneys are inclined and exhibit a significant out-of-plumb. According to the studies of Pallarés et al. (2011), permanent deformation can be due to ground settlements, creep, construction defects, or wind action. In particular, regarding the latter effect, chimneys coexisting in the same area exhibit out-of-plumb in the same direction: this can be explained by prevailing winds combined with creep phenomena that affect masonry, resulting in lack of verticality of the top portion of the structure. Out-of-plumb can induce cracks at the face of the chimney opposite to that experiencing tilting, if deformation is significant. Modern retrofitting technologies are conceived so as to make buildings safe without excessively modifying their mass and stiffness. FRPs (Fiber-Reinforced Polymers) are widely used to this end (Pallarés et al., 2009). The design of repair interventions can take advantage of refined numerical analyses, able to take non-linear effects into account. Combining modern structural analysis with modern technologies, restoration projects can be achieved that preserve architectural characteristics and enhance structural performances, including the ability to resist seismic actions. The object of this study is a masonry chimney located in the company town of Crespi d’Adda, near Bergamo in northern Italy. Because of its characteristics, this artefact is paradigmatic of industrial masonry chimneys of the end of the 19th century. The aim of the paper is to try and explain the origin of the crack pattern existing in the chimney, which was accurately detected by means of a direct survey carried out by a research group of Politecnico di Milano. The results of the research can be applied to the entire category of chimneys to which the artefact belongs, and may help designers in the definition of future repair interventions. 2. Description of the chimney The company town of Crespi d’Adda is one of the most interesting examples of industrial settlements in Italy and Europe of the 19th and 20th century, as the coexistence and proximity of dwellings and workplaces has lasted until the beginning of the second millennium – a situation that is unparalleled beyond the Alps. Because of its uniqueness, in addition to the state of conservation, valuable architecture and urban planning, in 1995 the town was included in the UNESCO World Heritage List.