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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Italian standard (NTC18, 2018). Connection between the concrete layer and the existing curbs is realized through L bent ϕ12 mm rebars, of B450C steel, with a spacing of 300 mm. In (a) and (b) the ground floor of the case-study building, in the state of art and retrofitted configurations, is presented. 3.2. Structural and energy assessment – SoA condition The case study building was first analyzed in its 'state of art' condition to assess its efficiency before the introduction of the retrofit system. For what concerns the seismic assessment, design seismic action was determined according to the Italian standard (D.M.17 gennaio, 2018), assuming the design working life V N equal to 50 years and a unitary usage coefficient C u . The foundation soil was assumed to be of category B and topographic category T1 was adopted, resulting in a return period for Life Safety (LS) limit state equal to 475 years and reference Peak Ground Acceleration (PGA) equal to 0.128g. Even if for existing masonry structures the behaviour factor can be even higher than 2.0 (Circ. n°7, 2019), being necessary the safety assessment also after the introduction of RC concrete walls for the retrofit – leading to a mixed masonry/RC structure - a conservative value of 1.50 was assumed, usually associated to non dissipative constructions. A FE numerical model was realized using SAP2000® software; bi-dimensional shell-type elements were used for modelling the masonry walls and floors, instead beam-type elements were used for the curbs. Results of the seismic analysis showed, predictably, that the structure has not sufficient capacity toward shear stresses by sliding and diagonal cracking and in-plane bending, while no relevant deficiencies were highlighted in terms of bending actions out-of plane. Summary of modal properties are presented in Table 2.

Fig. 2 (a) Plan view of the case-study building in the state of art condition; (b) Plan view of the case-study building in the retrofitted condition.

The structure’s energy performance was evaluated trough a simplified model run in modelling process with EnergyPlus TM and the web-based platform FREDS. For the purpose of modelling, geometry, internal and external surfaces, electrical equipment, lighting HCV system etc. were defined. Two main thermal zones of the building were identified, one at the ground floor and one at the first floor. Yearly analyses were run using input data of outdoor temperatures processed through the 'Typical Meteorological Year' (TMY) method. The main thermal properties used for characterizing the behavior of the walls were the thermal conductivity (λ), i.e., the quantity of heat that passes in unit time through a unit area of plate which thickness is unitary when its opposite faces differ in temperature by one degree and the thermal resistance (R), i.e., the temperature difference between two defined material surfaces that induces a unit heat flow rate through a unit area. Dynamic analyses of wall behavior were performed, both in free running and 'in-use' conditions, during summer and winter seasons. The objective is to evaluate the energy needs, the variation of the inner vertical wall face temperature, the variation of the energy transmitted by conduction through vertical surfaces and the temporal shift of the heat input/output point. In all thermal analyses performed in 'in-use' condition, the winter heating point was set at 20°C from 6AM to 10AM and from 4PM to 10PM, and at 17°C for all other hours of the day, for all days of the week except for Sunday, when the heating point was set at 20°C for all day.