*3.1.1 Thermal bridges and minimization of heat transmission losses*

Preliminary numerical investigations, in the framework of the monthly quasisteady state model, have been carried out to evaluate the contribution of thermal bridges to the energy balance of the building. Five different cases, labeled (a)–(e) have been considered:

**63**

**Figure 3.**

*Energy and Seismic Rehabilitation of RC Buildings through an Integrated Approach:...*

e.C2 configuration with thermal bridge contribution and additional thermal bar-

The thermal bridges considered in the simulations are pillars, external corners,

Results obtained by numerical simulations are presented in **Table 1**, where heat

The first conclusion is the importance of accounting for the thermal bridges for an accurate evaluation of heat thermal losses. Comparing results obtained from cases (c) and (d), one can conclude that the contribution of thermal bridges to the calculation of heat transmission losses is close to 40%, thus such contribution cannot be neglected. Therefore, a parametric study to define an effective solution to minimize thermal bridge losses has been carried out. To this end, a thermal barrier made up of a continuous external polystyrene coat has been added, by varying its thickness. **Figure 5** shows that a 4.0 cm coat appears an effective solution, being

Finally, the influence of thermal bridges is evaluated also by using the dynamic model. As an example, **Figure 6** shows the total heat transmission losses and the time evolution of the temperature of the internal air obtained in Palermo for the

Results show that, in dynamic conditions, the contribution of thermal bridges can influence dramatically the evaluation of transmission losses that can be under-

Numerical simulations have been performed both in quasi-static and dynamic

*3.1.2 Energy performances: monthly quasi-steady state and hourly dynamic models*

conditions for the two different locations under study, that is, Milano and

*Thermal bridges: corners (left side), roofs and ceiling (center), and pillars (right side).*

Thermal bridge contributions can be calculated by modeling the corresponding building component connections as input data for a 2D heat flow numerical code. As an example, in **Figure 4**, the temperature fields across the thermal bridge, obtained by means of the 2D heat flow code, are reported. Specifically, simulation refers to the cases (d) and (e), showing the effectiveness of the thermal barrier to

a.as-built (C1 configuration) without thermal bridges;

c.C2 configuration without thermal bridge contribution;

d.C2 configuration with thermal bridge contribution;

b.as built (C1 configuration) with thermal bridges;

*DOI: http://dx.doi.org/10.5772/intechopen.82581*

rier with different width, *s*.

minimize heat transmission losses.

and roof-to-wall interfaces, as shown in **Figure 3**.

transmission losses are reported for the cases (a)–(e).

able to reduce thermal bridge losses up to 35%.

configuration C2.

estimated up to a factor 2.

*Energy and Seismic Rehabilitation of RC Buildings through an Integrated Approach:... DOI: http://dx.doi.org/10.5772/intechopen.82581*

a.as-built (C1 configuration) without thermal bridges;

b.as built (C1 configuration) with thermal bridges;

*Green Energy Advances*

model [21].

evaluating the structural capacity.

namely Milano and Palermo.

31st of March and collects about 150 cities).

*3.1.1 Thermal bridges and minimization of heat transmission losses*

**3.1 Energy analysis**

have been considered:

strength and the elastic modulus, as suggested in [23].

**3. Thermal and seismic rehabilitation design**

existing buildings under study consists of the following:

deformation capacity experienced in case of failure in shear. On the basis of the mechanical properties of the constituent materials typically found in real buildings of the period under consideration [20], mean concrete strength value (fcm) equal to 20 MPa, and mean steel strength value (fym) equal to 400 MPa were assumed in

In the different configurations considered in the study, infill panels were modeled by using a nonlinear equivalent diagonal strut according to the Bertoldi

Consistent with experimental results (e.g., [22]), for the infill type considered in the as-built configuration, the compressive strength and the elastic modulus are equal to 1.1 and 1800 MPa, respectively. As for infills in both C2 and C3 configuration, the adopted values are 4.0 and 3300 MPa, respectively, for the compressive

The integrated intervention here investigated for the rehabilitation of the RC

• replacing the external existing infill panel of the as-built configuration (C1) with new one having better thermal insulation properties (C2 configuration);

• adding new infill panels to the as-built configuration (C1) placed on new RC

According to the European Standard EN ISO 6946, 10077, and 12631, the total thermal transmittances for cases C1, C2, and C3 are 0.69, 0.28, and 0.28 W m<sup>−</sup><sup>2</sup>

respectively. In dynamic conditions, heat transfer coefficients, including the thermal bridge contribution, have been calculated according to the ISO 13789:2017. In the following, starting from the assessment results obtained for the as-built configuration (C1), both energy and seismic performances of the two proposed integrated solutions have been evaluated with respect to two different locations,

Numerical simulations have been performed in order to calculate the energy need in configurations C1, C2, and C3. Results have been obtained in both quasistatic and dynamic condition. Two different locations have been considered: (i) Milan, located in the Italian climate zone E (heating degree days in the range 2101–3000, heating period from the 15th of October to the 15th of April and collects about 4000 cities), and (ii) Palermo, located in the Italian climate zone B (heating degree days in the range 601–900, heating period from the 1st of December to the

Preliminary numerical investigations, in the framework of the monthly quasisteady state model, have been carried out to evaluate the contribution of thermal bridges to the energy balance of the building. Five different cases, labeled (a)–(e)

 K<sup>−</sup><sup>1</sup> ,

frames effectively connected to the existing ones (C3 configuration).

**62**

c.C2 configuration without thermal bridge contribution;


The thermal bridges considered in the simulations are pillars, external corners, and roof-to-wall interfaces, as shown in **Figure 3**.

Thermal bridge contributions can be calculated by modeling the corresponding building component connections as input data for a 2D heat flow numerical code. As an example, in **Figure 4**, the temperature fields across the thermal bridge, obtained by means of the 2D heat flow code, are reported. Specifically, simulation refers to the cases (d) and (e), showing the effectiveness of the thermal barrier to minimize heat transmission losses.

Results obtained by numerical simulations are presented in **Table 1**, where heat transmission losses are reported for the cases (a)–(e).

The first conclusion is the importance of accounting for the thermal bridges for an accurate evaluation of heat thermal losses. Comparing results obtained from cases (c) and (d), one can conclude that the contribution of thermal bridges to the calculation of heat transmission losses is close to 40%, thus such contribution cannot be neglected. Therefore, a parametric study to define an effective solution to minimize thermal bridge losses has been carried out. To this end, a thermal barrier made up of a continuous external polystyrene coat has been added, by varying its thickness. **Figure 5** shows that a 4.0 cm coat appears an effective solution, being able to reduce thermal bridge losses up to 35%.

Finally, the influence of thermal bridges is evaluated also by using the dynamic model. As an example, **Figure 6** shows the total heat transmission losses and the time evolution of the temperature of the internal air obtained in Palermo for the configuration C2.

Results show that, in dynamic conditions, the contribution of thermal bridges can influence dramatically the evaluation of transmission losses that can be underestimated up to a factor 2.

#### *3.1.2 Energy performances: monthly quasi-steady state and hourly dynamic models*

Numerical simulations have been performed both in quasi-static and dynamic conditions for the two different locations under study, that is, Milano and

**Figure 3.** *Thermal bridges: corners (left side), roofs and ceiling (center), and pillars (right side).*

#### **Figure 4.**

*Thermal bridge simulation of pillars with (on the bottom) and without (on the top) additional 40 mm of thermal barrier.*


#### **Table 1.**

*Total heat transmission losses (in [*kWh m<sup>−</sup><sup>2</sup> K<sup>−</sup><sup>1</sup> *]).*

Palermo. In **Figure 7**, the results computed with the monthly quasi-steady state and hourly dynamic models are compared, both in cooling and in heating conditions. In the simulations, the building volume is divided considering two thermal zones, that is, night and day rooms, with different set point temperatures (19 and 21°C), and the HVAC system is considered active only for 10 hours/day in the case of dynamic simulation. Results show that dynamic and static methods could produce different results due to the capability of the dynamic model of reproducing more realistically the behavior of the building (HVAC system, internal gains or losses,…).

Finally, in **Table 2**, the total thermal energy for heating, *Q H,* and cooling, *QC*, are reported, both for Milano and Palermo by using the hourly dynamic and the monthly quasi-steady state models. Results show the effectiveness of C2 and C3 energy retrofits. In particular, C3 configuration is the best solution both in Palermo and Milano from the point of view of the energy saving. However, it should be highlighted that this is a partial result, as the analysis of the seismic performance, together with the cost of the total retrofit intervention, must be considered in a complete analysis.

**65**

**3.2 Seismic analyses**

**Figure 5.**

**Figure 6.**

*considering an additional thermal barrier.*

*model and refer to the building located in Palermo.*

*Energy and Seismic Rehabilitation of RC Buildings through an Integrated Approach:...*

Seismic performances have been evaluated through the incremental dynamic analysis (IDA) [7]. In order to account for the effects on the structural response due to record-to-record variability, 10 accelerograms selected in the RINTC project [24] and scaled up to the collapse have been considered. The main seismic parameters of the considered accelerograms are reported in [9] and briefly summarized in **Table 3**. Results are reported in **Figure 8**. Specifically, the IDA median curves, evaluated for the considered configurations in terms of spectral pseudoacceleration value corresponding to the scaling factor of the record and the maximum base shear value, are displayed separately for X (**Figure 8a**) and Y (**Figure 8b**) in-plane direction. The spectral-pseudoacceleration Se(T0) has been evaluated at the fundamental period of each considered configuration. In the same figure, the points relevant to both damage limitation (DLLS) and life safety (LSLS) limit state, calculated in

*Total heat transmission losses obtained for the C2 configuration. In the simulations, thermal bridges (TB) and an additional thermal barrier of 4 cm are considered. Simulations are obtained by means of the dynamic* 

*Total heat transmission losses obtained for the C2 configuration including the effects of thermal bridges and* 

With reference to C1 configuration (i.e., "as-built"), the seismic intensities evaluated in the X direction at DLLS and LSLS are equal to 0.105 and 0.163 g, respectively. In the Y direction, mainly due to the role of the staircase substructure (which determines a greater stiffness with respect to the X direction and a brittle behavior of the relevant short columns), DLLS is achieved at 0.138 g, which is about

accordance with the Italian code [25], are also displayed.

*DOI: http://dx.doi.org/10.5772/intechopen.82581*

*Energy and Seismic Rehabilitation of RC Buildings through an Integrated Approach:... DOI: http://dx.doi.org/10.5772/intechopen.82581*

#### **Figure 5.**

*Green Energy Advances*

**Figure 4.**

**Table 1.**

*thermal barrier.*

**64**

internal gains or losses,…).

*Total heat transmission losses (in [*kWh m<sup>−</sup><sup>2</sup>

complete analysis.

Palermo. In **Figure 7**, the results computed with the monthly quasi-steady state and hourly dynamic models are compared, both in cooling and in heating conditions. In the simulations, the building volume is divided considering two thermal

*Thermal bridge simulation of pillars with (on the bottom) and without (on the top) additional 40 mm of* 

*Qtr* 91.76 116.21 69.78 104.05 75.44 *Qtr* pillars 91.83 75.13 *Qtr* pillars and corners 93.33 75.44

**Case a Case b Case c Case d Case e (s = 40mm)**

Finally, in **Table 2**, the total thermal energy for heating, *Q H,* and cooling, *QC*, are reported, both for Milano and Palermo by using the hourly dynamic and the monthly quasi-steady state models. Results show the effectiveness of C2 and C3 energy retrofits. In particular, C3 configuration is the best solution both in Palermo and Milano from the point of view of the energy saving. However, it should be highlighted that this is a partial result, as the analysis of the seismic performance, together with the cost of the total retrofit intervention, must be considered in a

zones, that is, night and day rooms, with different set point temperatures (19 and 21°C), and the HVAC system is considered active only for 10 hours/day in the case of dynamic simulation. Results show that dynamic and static methods could produce different results due to the capability of the dynamic model of reproducing more realistically the behavior of the building (HVAC system,

 K<sup>−</sup><sup>1</sup> *]).*

*Total heat transmission losses obtained for the C2 configuration including the effects of thermal bridges and considering an additional thermal barrier.*

#### **Figure 6.**

*Total heat transmission losses obtained for the C2 configuration. In the simulations, thermal bridges (TB) and an additional thermal barrier of 4 cm are considered. Simulations are obtained by means of the dynamic model and refer to the building located in Palermo.*

#### **3.2 Seismic analyses**

Seismic performances have been evaluated through the incremental dynamic analysis (IDA) [7]. In order to account for the effects on the structural response due to record-to-record variability, 10 accelerograms selected in the RINTC project [24] and scaled up to the collapse have been considered. The main seismic parameters of the considered accelerograms are reported in [9] and briefly summarized in **Table 3**.

Results are reported in **Figure 8**. Specifically, the IDA median curves, evaluated for the considered configurations in terms of spectral pseudoacceleration value corresponding to the scaling factor of the record and the maximum base shear value, are displayed separately for X (**Figure 8a**) and Y (**Figure 8b**) in-plane direction. The spectral-pseudoacceleration Se(T0) has been evaluated at the fundamental period of each considered configuration. In the same figure, the points relevant to both damage limitation (DLLS) and life safety (LSLS) limit state, calculated in accordance with the Italian code [25], are also displayed.

With reference to C1 configuration (i.e., "as-built"), the seismic intensities evaluated in the X direction at DLLS and LSLS are equal to 0.105 and 0.163 g, respectively. In the Y direction, mainly due to the role of the staircase substructure (which determines a greater stiffness with respect to the X direction and a brittle behavior of the relevant short columns), DLLS is achieved at 0.138 g, which is about

#### **Figure 7.**

*Total transmission losses (heating and cooling) obtained for the C2 configuration. Simulations are obtained by means of the monthly quasi-steady state and hourly dynamic models and refer to the building located in Palermo.*


#### **Table 2.**

*Total thermal energy for heating and cooling in Milano and Palermo.*

30% higher than that evaluated in the X direction (0.105 g), whereas a remarkably lower value (0.110 g) than that evaluated in the X direction (0.163 g) is found for LSLS.

In order to estimate the seismic deficit, the above reported intensity values (capacity, Se,C) have been compared with the seismic hazard (demand, Se,D) evaluated for Milan and Palermo (representative of sites with low and medium seismic hazard) according to the Italian hazard map [26] (soil A). The ratio between the capacity and the demand value (α = Se,C/Se,D) for both limit states has been computed, and the results are reported in **Table 4**.

Except for the site of Palermo at LS limit state, both αDL and αLS are always higher than 1 (i.e., no seismic intervention is required). αLS evaluated for Palermo is equal to 0.81, thus asking for a strengthening intervention to guarantee adequate structural safety.

As a consequence of the greater mechanical properties of the infill panels adopted for C2 configuration, a greater base shear value is found with respect to C1 configuration, as shown in **Figure 8**. In terms of seismic intensity values relevant to both DLLS and LSLS, they are equal to 0.130 and 0.197 g in the X direction (to be compared with 0.105 and 0.163 g in the C1 configuration, respectively), while, in

**67**

**Table 3.**

**Figure 8.**

**Table 4.**

*Energy and Seismic Rehabilitation of RC Buildings through an Integrated Approach:...*

**ID PGA (g) PGV (cm/s) Se,max (g) HI (m)** 0.046 1.61 0.167 0.049 0.035 2.13 0.125 0.054 0.043 0.41 0.183 0.054 0.021 0.83 0.086 0.052 0.070 0.26 0.339 0.047 0.050 2.37 0.089 0.052 0.029 0.45 0.108 0.061 0.009 0.85 0.037 0.083 0.026 0.31 0.105 0.064 0.028 0.56 0.147 0.055

*Seismic parameters of the considered accelerograms in terms of peak ground acceleration (PGA), peak ground* 

*velocity (PGV), maximum spectral pseudoacceleration (Se,max), and Housner intensity (HI).*

the Y direction, they are 0.189 and 0.168 g (0.138 and 0.110 g in the C1 configuration, respectively). Consequently, the minimum αLS value evaluated for the site of

*α ratio values between seismic capacity Se,C and demand Se,D evaluated for both DL and LS limit state.*

*Spectral pseudo-acceleration versus maximum base shear curves relevant to the three considered configurations,* 

**Site Se,C (g) Se,D (g) αDL = Se,C/Se,D Se,C (g) Se,D (g) αLS = Se,C/Se,D** Milan 0.105 0.015 7.0 0.110 0.042 2.6 Palermo 0.039 2.7 0.135 0.81

*obtained for X (a) and Y (b) direction by considering median values from IDA analyses.*

**DLLS LSLS**

As for C3 configuration (i.e., new infilled RC frames added to the as-built configuration C1 and effectively connected to the existing frames, **Figure 9**), **Figure 8** summarizes the results obtained from the IDA analyses and the comparison with the other configurations (C1 and C2). In terms of seismic capacity evaluated at the two considered limit states, the values at LSLS are equal to 0.430 and 0.450 g for X and

Palermo goes from 0.81 to 0.93 (**Table 5**).

*DOI: http://dx.doi.org/10.5772/intechopen.82581*

*Energy and Seismic Rehabilitation of RC Buildings through an Integrated Approach:... DOI: http://dx.doi.org/10.5772/intechopen.82581*


#### **Table 3.**

*Green Energy Advances*

**66**

LSLS.

**Table 2.**

**Figure 7.**

*Palermo.*

Dynamic (kWh)

Quasisteady state (kWh)

structural safety.

30% higher than that evaluated in the X direction (0.105 g), whereas a remarkably lower value (0.110 g) than that evaluated in the X direction (0.163 g) is found for

*Total transmission losses (heating and cooling) obtained for the C2 configuration. Simulations are obtained by means of the monthly quasi-steady state and hourly dynamic models and refer to the building located in* 

**C1 C2 C3 C1 C2 C3**

*Q H* 28,773.69 21,078.01 9013.55 12,627.31 8533.53 8748.46 *QC* 5218.24 6345.19 6916.87 7101.93 7795.36 8075.09

*Q H* 18,665.85 14,922.19 15,205.30 5443.9 4129.12 4098.47 *Q C* 3695.57 4025.78 3809.08 7142.80 7275.69 7401.05

**Case Milano Palermo**

In order to estimate the seismic deficit, the above reported intensity values (capacity, Se,C) have been compared with the seismic hazard (demand, Se,D) evaluated for Milan and Palermo (representative of sites with low and medium seismic hazard) according to the Italian hazard map [26] (soil A). The ratio between the capacity and the demand value (α = Se,C/Se,D) for both limit states has been com-

Except for the site of Palermo at LS limit state, both αDL and αLS are always higher than 1 (i.e., no seismic intervention is required). αLS evaluated for Palermo is equal to 0.81, thus asking for a strengthening intervention to guarantee adequate

As a consequence of the greater mechanical properties of the infill panels adopted for C2 configuration, a greater base shear value is found with respect to C1 configuration, as shown in **Figure 8**. In terms of seismic intensity values relevant to both DLLS and LSLS, they are equal to 0.130 and 0.197 g in the X direction (to be compared with 0.105 and 0.163 g in the C1 configuration, respectively), while, in

puted, and the results are reported in **Table 4**.

*Total thermal energy for heating and cooling in Milano and Palermo.*

*Seismic parameters of the considered accelerograms in terms of peak ground acceleration (PGA), peak ground velocity (PGV), maximum spectral pseudoacceleration (Se,max), and Housner intensity (HI).*

#### **Figure 8.**

*Spectral pseudo-acceleration versus maximum base shear curves relevant to the three considered configurations, obtained for X (a) and Y (b) direction by considering median values from IDA analyses.*


#### **Table 4.**

*α ratio values between seismic capacity Se,C and demand Se,D evaluated for both DL and LS limit state.*

the Y direction, they are 0.189 and 0.168 g (0.138 and 0.110 g in the C1 configuration, respectively). Consequently, the minimum αLS value evaluated for the site of Palermo goes from 0.81 to 0.93 (**Table 5**).

As for C3 configuration (i.e., new infilled RC frames added to the as-built configuration C1 and effectively connected to the existing frames, **Figure 9**), **Figure 8** summarizes the results obtained from the IDA analyses and the comparison with the other configurations (C1 and C2). In terms of seismic capacity evaluated at the two considered limit states, the values at LSLS are equal to 0.430 and 0.450 g for X and


#### **Table 5.**

*Comparison between seismic capacity values and hazard demand relevant to as-built and postintervention configurations evaluated for LS limit state.*

**Figure 9.** *C3 configuration: in plan layout of the retrofitted building (a) and 3D view of the model (b).*

Y directions, respectively, while for DLLS, intensity values are 0.170 and 0.215 g for X and Y directions, respectively. Consequently, a full seismic rehabilitation (i.e., αLS ratio greater than 1) has been achieved also for Palermo, as reported in **Table 5**.

### **4. Conclusions**

In the present work, an application of integrated rehabilitation intervention on reinforced concrete (RC) existing buildings has been presented. A case study located in two different cities, Milano and Palermo, having different climatic conditions and seismic hazard values, has been investigated.

The building under study has been analyzed considering three different configurations, with different arrangement and features of the infill panels, in order to highlight their role on both thermal and seismic performances. Quasi-static and dynamic methodologies have been used for the calculation of the energy demand, highlighting the importance of accounting for thermal bridges in the investigations. As for seismic performance, the results of the incremental nonlinear dynamic analyses show that infill panels having greater thermal and mechanical properties increase the seismic capacity. Nevertheless, a full seismic rehabilitation for the site with the highest seismic hazard (i.e., Palermo) has been achieved only by strengthening the RC structure with additional RC frames.

Future work, besides including additional case studies (building types, different seismic and climate sites,…), will be devoted to set up and propose a methodology

**69**

**Author details**

provided the original work is properly cited.

© 2019 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

Antonio D'Angola\*, Vincenzo Manfredi, Angelo Masi and Marianna Mecca

Scuola di Ingegneria, Università della Basilicata, Potenza, Italy

\*Address all correspondence to: antonio.dangola@unibas.it

*Energy and Seismic Rehabilitation of RC Buildings through an Integrated Approach:…*

for integrated rehabilitation interventions. Further, economic aspects will be better investigated with the aim of finding the cost-optimal integrated retrofit solution including the impact of the expected economic losses due to seismic damage

*DOI: http://dx.doi.org/10.5772/intechopen.82581*

throughout the building life cycle.

*Energy and Seismic Rehabilitation of RC Buildings through an Integrated Approach:… DOI: http://dx.doi.org/10.5772/intechopen.82581*

for integrated rehabilitation interventions. Further, economic aspects will be better investigated with the aim of finding the cost-optimal integrated retrofit solution including the impact of the expected economic losses due to seismic damage throughout the building life cycle.
