PSI - Issue 44

Silvia Caprili et al. / Procedia Structural Integrity 44 (2023) 1030–1037 Sivia Caprili et al. / Structural Integrity Procedia 00 (2022) 000–000

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allowed to approximate the wall behaviour with that of simply supported beam subjected to a force uniformly distributed with the height. Results showed a general increase of the capacity toward shear stresses by sliding and diagonal cracking and in-plane bending. Figure 3 shows an example of the results obtained in respect of shear actions for the ground floor walls in the 'state of art' (Fig. 3a) and the 'design state' configurations (Fig. 3b). The structural elements that did not meet the safety requirements are marked by red colour, providing the D/C corresponding ratio. The increment of the safety level was also measured through the ζ E parameter. Specifically, the ζ E parameter resulted in an increase of 0.3 decimal points, moving from 0.50 to 0.80. In terms of energy performance, as the infill walls were used only on the building's perimeter, only the thermal properties of vertical walls have been changed to make a comparison between the structure in the 'state of art' condition and after the retrofitting intervention. The first remarkable result obtained was the variation of the thermal transmittance (U) of the building. Before the retrofit intervention, it was equal to 0.947 W/m²K at the ground floor and to 1.059 W/m²K at the first floor. In the 'design state', it was instead 0.267 W/m²K at the ground floor and to U = 0.276 W/m²K at the first floor, thus showing a decrement of about 70%. Going deeper into the dynamic behavior of the of external wall, Table 3 and Fig. 4 show the results of analyses for walls located Nord (N-wall) for the winter season, and walls located Sud (S-wall) for summer season.

Table 3. Result of the thermal analyses, in-use conditions. Model

Energy needs, winter season ( kWh/m 2 )

Mean inner face temperature, N-wall, winter week ( °C )

Mean energy transmitted by conduction, N-wall, winter week ( W/m 2 )

Mean inner face temperature, S-wall, summer week ( °C )

Mean energy transmitted by conduction, S-wall, summer week ( W/m 2 )

State of art Design state

80

14

-1554.62

29

39.78

66

16

-405.38

29

-65.56

Please note that the heat flow due to conduction through the inner face of the wall is negative if outgoing from the building and positive if incoming. By exclusively changing the composition of the outer wall enclosure, during winter season, the inner face temperature rose by one degree while the energy lost by conduction from the walls decreased of about 70%, Fig. 4(a). In contrast, during summer season, there are no appreciable changes in the values considered, in line with the type of interventions defined as external-coat insulation, the important difference was found to be the shift in heat input point, Fig. 4(b). As a result of the intervention, the wall acquired thermal inertia, and thus is able to phase heat flows (Leccese et al., 2018). The shift in heat output and input point have thus been calculated for the N-wall and the S-wall, throughout the TMY, as 1h 52 min +/- 58 min and 1 h 34 min +/- 1 h 5 min respectively. 3.4. Indoor comfort To complete the energy performance analysis, a numerical assessment of the global and local indoor thermal comfort was carried out. For the evaluation of the first, the Predicted Mean Vote (PMV) model (ISO 7730, 2005) and the Adaptive Comfort Model (Yao et al., 2022) were used. The PMV model has proven to be particularly well suited to represent the indoor thermal comfort during the winter season and in the 'in-use' condition. Analyses have been carried out in day and night condition, where day is considered from 7AM to 10PM, while the remaining hours are considered night-time. Environmental parameters (air temperature, air velocity, relative humidity, and radiant temperature) are taken from the model. Personal parameters (metabolism and clothing insulation) were taken as 1.2 met (day) and 0.8 met (night) for the metabolism and 1.0 clo (day) and 2.0 clo (night) for the clothing. The PMV model sets different levels of comfort based on a rating between −3 and 3, where −3 corresponds to a very cold body thermal sensation, and 3 to a very hot one. Typically, the goal is to keep the PMV value between −0.5 and 0.5, but it’s still considered acceptable to be in a range of -1 to +1. Result of the analyses are showed in Table

4.