PSI - Issue 64

Benedetto Manganelli et al. / Procedia Structural Integrity 64 (2024) 1720–1726 B.Manganelli, P. De Paola, F.P. Del Giudice/ Structural Integrity Procedia 00 (20) 000 – 000

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rates of decline. The slower rate is associated with the natural aging of materials, referring to the physical wear and tear that occurs over time; while a faster rate is linked to changes dictated by aesthetic reasons (e.g., new materials or construction trends) or legal reasons (e.g., fire safety or the presence of materials no longer allowed, such as asbestos), or due to variations in the social context (for example, changes in user demands). It is important to emphasize the difference between service life and actual useful life. Awano (2006) separates the life of a building into two categories: "real life," which corresponds to what we have called service life here, conditioned by the physical conditions of the building; and the actual useful life, which the author considers conditioned by the ability of a building to fulfill its function and other performance criteria. Haapio and Viitaniemi (2008) refer to useful life as the period during which a building or component is able to meet the objective and subjective needs of users without unacceptable maintenance costs. It should be noted that while routine maintenance is essential to compensate for the loss of performance capacity caused by physical wear and tear, modernization interventions are essential to compensate for functional obsolescence, which we can classify as extraordinary maintenance (Bezelga et al., 1985; Roger et al., 2017). Due to the continuous growth of quality standards, the initial quality level, even in the absence of physical wear and tear, may fall below the minimum acceptable level. In practice, a building element, although still efficient, therefore not damaged or dysfunctional, can still be obsolete because it is no longer able to meet the users' needs in light of the introduction of new standards (Lemer, 1996). Bezelga and Neto (1985) introduce the concept of demolition threshold , understood as the moment when the new performance standard required by users (functional obsolescence) exceeds the quality level of the building, which has also reached it due to physical wear and tear. Other authors (Mansfield, J.R. et al., 2008; Pourebrahimi, M. et al., 2020; Grover, R. et al., 2015; Thomsen, A. et al., 2011) link the end of the useful life of an obsolete building (to which a demolition threshold is therefore associated) to the loss of performance or utility, which can be caused by its physical deterioration or by economic and social motivations, technological or political changes, or even fluctuations in user needs. Thomsen et al. (2009) consider it very complicated to practically define the demolition threshold or the moment after which a building no longer meets the essential performance requirements. Especially when, even though the building is subject to regular and adequate maintenance activities, demolition occurs for social, legal, or economic efficiency reasons, i.e., before reaching its limit of useful service life (Kohler, N. et al., 2002; Farahani, A. et al., 2019). All the literature illustrated so far has discussed the useful life and the related need for demolition/replacement of the building now outdated due to physical decay and/or obsolescence, exclusively referring to the building itself. In practice, even when external factors are mentioned, whether they are social, cultural, aesthetic, or economic factors determining obsolescence, these are defined in the relationship between users and the building. There is never a discussion of how land rent or external obsolescence can influence the choice of demolition and reconstruction. 3. The Analysis of Economic Feasibility The originality of this work lies in the attempt to analyze the market value dynamics of a building by separating the two components, the land and the structure. This condition is useful to define a demolition threshold, understood as the moment at which it becomes economically convenient to demolish and replace the building. In Figure 1, LV indicates the land value at the time of building construction, UR the urban rent which is assumed to have a positive gradient. BC is the cost of construction (or reconstruction) of the building, while DC is the depreciation of the cost due to physical wear and tear as well as functional and economic obsolescence of the structure. The sum of these terms provides the dynamics of the market value (MV 0 ) of the building, or the land and structure together. It is evident that at the end of the useful service life, which coincides with the zeroing of the structure's cost value, the market value coincides with the value of the land alone. A superficial assessment might indicate this moment as the demolition threshold, or the moment when it would be advantageous to demolish and replace the building. However, it must be noted that demolition incurs a cost, which includes the expenses for the demolition operation itself, as well as the costs for transporting and disposing of materials (DK) . Therefore, replacing the building involves both the cost of new construction and the cost of demolition of the old one. For the replacement/regeneration operation to be economically feasible, the final value ( MV f ) must exceed the costs incurred.