**1. Introduction**

In Europe, about 25 billion m<sup>2</sup> of available floor space (data relevant to 27 EU member states in 2011 plus Switzerland and Norway) was built up in the past. A predominant part of this surface, about 75%, is made up of residential buildings (64% single family houses, 36% apartment blocks), while the other part (25%) consists of more complex and heterogeneous nonresidential buildings. More than 40% of residential buildings were constructed before the 1960s, with the largest percentages of older buildings in the United Kingdom, Denmark, Sweden, France, Czech Republic, and Bulgaria [1]. As a result, beyond the well-known deficit of seismic protection, dramatically pointed out by past earthquakes, also the energy performances of the European buildings are expected to be generally poor. In fact, energy consumed in buildings is one of the main CO2 emission sources in Europe.

As for Italy, most of the residential buildings (77%) were constructed before 1981, when only 25% of the national territory was classified as seismic. These buildings were not designed considering seismic actions; therefore, they are generally characterized by high vulnerability, as clearly shown by recent earthquakes (e.g., L'Aquila 2009, Emilia 2012, central Italy 2016) [2–5].

In addition to seismic deficit, the Italian building stock is also characterized by a large deficit of thermal insulation. In fact, the first regulation, addressing thermal performance criteria, was introduced in 1991 [6], when about 88% of the present Italian building stock had already been realized.

Due to the huge number of buildings having inadequate seismic and energy performances, both in Europe and in Italy, an integrated approach in the design of interventions able to provide multiple beneficial effects is strongly required in view of deploying an effective rehabilitation program. On the contrary, uncoupled rehabilitation solutions appear ineffective. In fact, in earthquake-prone areas, thermal rehabilitation interventions designed neglecting seismic actions could determine an increase of the exposure in terms of building value without adequate seismic protection. Similarly, seismic retrofitting interventions paying little or no attention to thermal rehabilitation could compromise comfort and energy maintenance costs since they can induce higher heat loss (e.g., by simply adding RC shear walls). As an example, interventions that either do not eradicate or—even worse—introduce thermal bridges, due to discontinuities or gaps in the insulation material, can compromise thermal insulation.

In the framework of an integrated approach, the chapter focuses on the impact on the seismic performance of some rehabilitation techniques generally adopted to enhance the thermal performance of infill walls. To this purpose, incremental dynamic analyses (IDAs, [7]) have been carried out on a prototype RC building representative of the existing building stock—before and after thermal rehabilitation. Specifically, an intervention carried out by replacing the existing masonry infill walls with new elements able to ensure an adequate thermal insulation is considered. Furthermore, the improvement in both seismic and thermal performances through the so-called "double skin" [8, 9] intervention technique, that is, by adding new infilled frames adequately linked to the existing ones, is analyzed.

Energy performances have been investigated following the European standard methods by means of a quasi-steady state approach, based on monthly averaged climate data, and of a dynamic approach, based on hourly climate data. Both energy and seismic analyses have been performed considering two different Italian cities, namely Palermo (Southern Italy) and Milan (Northern Italy), characterized by different climatic conditions and seismic hazard.

## **2. Case study: building type description and modeling**

A six-storey RC framed structure representative of the nonseismic post-1971 Italian building stock has been considered as case study. It has a rectangular shape in plan (**Figure 1**) with total dimensions 21.4 × 11.8 m2 (X and Y direction, respectively) and constant interstorey height equal to 3.05 m. As a consequence of the design carried out only for vertical load and the orientation of the one-way RC slab spanning along the longitudinal X direction, frames are arranged in the transversal Y direction only. Rigid beams (0.30 × 0.50 m2 ) are arranged along the exterior frames,

**59**

tioned zones.

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

while internal beams are flexible (0.70 × 0.25 and 1.00 × 0.25 m2

the longitudinal direction X, rigid beams are present only in the exterior frames. Columns have generally cross-sectional dimensions equal to 0.30 × 0.30 m2

*In plan layout of the building type under study (a) and three-dimensional (3D) view of the model (b).*

for some columns of the lower storeys whose dimensions range from 0.30 × 0.40

respect to the Y direction and has knee-type beam with dimension 0.30 × 0.50 m2

constituted by two hollow brick walls (8 cm + 12 cm, respectively, internal and external layer) with an air gap (10 cm) and internal/external cement plaster/finish coats (2 cm + 2 cm). Windows are made by wood and a single glass and are charac-

Reinforcement details have been obtained by means of a simulated design procedure [10] with reference to the codes in force and the constructive practice of

Both energy and seismic analyses have been carried out by considering three

2.C2: external existing layer of the as-built infill (12 cm thick) replaced by new

3.C3: new 20-cm-thick infill panels placed on new RC frames added to the asbuilt configuration (C1) and effectively connected to the existing frames.

The energy balance has been performed in the framework of the monthly quasisteady state and of the hourly dynamic approaches, focusing on the second floor of

The boundaries for the calculation of the heating and cooling energy values consist of all the elements separating the conditioned single-zone space from the external environment or unconditioned spaces: external walls and windows. Floors and ceiling are excluded from the envelope representing boundaries with condi-

of useful floor area, *V* = 751.96 m3

one (20 cm thick) with high thermal insulation properties;

surface-to-volume ratio *S/V* = 0.6, being *S* the total external surface.

According to the considered construction period, infill panel is a multilayer type

. The staircase substructure is placed in a symmetric position with

). Specifically, along

, except

of volume, and

.

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

to 0.30 × 0.55 m2

**Figure 1.**

the period.

different configurations:

**2.1 Energy retrofitting modeling**

the building, with *Su* = 219.68 m2

1.C1: as-built;

terized by high values of transmittance.

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

#### **Figure 1.**

*Green Energy Advances*

Czech Republic, and Bulgaria [1]. As a result, beyond the well-known deficit of seismic protection, dramatically pointed out by past earthquakes, also the energy performances of the European buildings are expected to be generally poor. In fact, energy consumed in buildings is one of the main CO2 emission sources in Europe. As for Italy, most of the residential buildings (77%) were constructed before 1981, when only 25% of the national territory was classified as seismic. These buildings were not designed considering seismic actions; therefore, they are generally characterized by high vulnerability, as clearly shown by recent earthquakes

In addition to seismic deficit, the Italian building stock is also characterized by a large deficit of thermal insulation. In fact, the first regulation, addressing thermal performance criteria, was introduced in 1991 [6], when about 88% of the present

Due to the huge number of buildings having inadequate seismic and energy performances, both in Europe and in Italy, an integrated approach in the design of interventions able to provide multiple beneficial effects is strongly required in view of deploying an effective rehabilitation program. On the contrary, uncoupled rehabilitation solutions appear ineffective. In fact, in earthquake-prone areas, thermal rehabilitation interventions designed neglecting seismic actions could determine an increase of the exposure in terms of building value without adequate seismic protection. Similarly, seismic retrofitting interventions paying little or no attention to thermal rehabilitation could compromise comfort and energy maintenance costs since they can induce higher heat loss (e.g., by simply adding RC shear walls). As an example, interventions that either do not eradicate or—even worse—introduce thermal bridges, due to discontinuities or

In the framework of an integrated approach, the chapter focuses on the impact on the seismic performance of some rehabilitation techniques generally adopted to enhance the thermal performance of infill walls. To this purpose, incremental dynamic analyses (IDAs, [7]) have been carried out on a prototype RC building representative of the existing building stock—before and after thermal rehabilitation. Specifically, an intervention carried out by replacing the existing masonry infill walls with new elements able to ensure an adequate thermal insulation is considered. Furthermore, the improvement in both seismic and thermal performances through the so-called "double skin" [8, 9] intervention technique, that is, by adding new infilled frames adequately linked to the existing ones, is analyzed. Energy performances have been investigated following the European standard methods by means of a quasi-steady state approach, based on monthly averaged climate data, and of a dynamic approach, based on hourly climate data. Both energy and seismic analyses have been performed considering two different Italian cities, namely Palermo (Southern Italy) and Milan (Northern Italy), characterized by

(e.g., L'Aquila 2009, Emilia 2012, central Italy 2016) [2–5].

gaps in the insulation material, can compromise thermal insulation.

Italian building stock had already been realized.

different climatic conditions and seismic hazard.

plan (**Figure 1**) with total dimensions 21.4 × 11.8 m2

direction only. Rigid beams (0.30 × 0.50 m2

**2. Case study: building type description and modeling**

A six-storey RC framed structure representative of the nonseismic post-1971 Italian building stock has been considered as case study. It has a rectangular shape in

and constant interstorey height equal to 3.05 m. As a consequence of the design carried out only for vertical load and the orientation of the one-way RC slab spanning along the longitudinal X direction, frames are arranged in the transversal Y

(X and Y direction, respectively)

) are arranged along the exterior frames,

**58**

*In plan layout of the building type under study (a) and three-dimensional (3D) view of the model (b).*

while internal beams are flexible (0.70 × 0.25 and 1.00 × 0.25 m2 ). Specifically, along the longitudinal direction X, rigid beams are present only in the exterior frames. Columns have generally cross-sectional dimensions equal to 0.30 × 0.30 m2 , except for some columns of the lower storeys whose dimensions range from 0.30 × 0.40 to 0.30 × 0.55 m2 . The staircase substructure is placed in a symmetric position with respect to the Y direction and has knee-type beam with dimension 0.30 × 0.50 m2 .

According to the considered construction period, infill panel is a multilayer type constituted by two hollow brick walls (8 cm + 12 cm, respectively, internal and external layer) with an air gap (10 cm) and internal/external cement plaster/finish coats (2 cm + 2 cm). Windows are made by wood and a single glass and are characterized by high values of transmittance.

Reinforcement details have been obtained by means of a simulated design procedure [10] with reference to the codes in force and the constructive practice of the period.

Both energy and seismic analyses have been carried out by considering three different configurations:


#### **2.1 Energy retrofitting modeling**

The energy balance has been performed in the framework of the monthly quasisteady state and of the hourly dynamic approaches, focusing on the second floor of the building, with *Su* = 219.68 m2 of useful floor area, *V* = 751.96 m3 of volume, and surface-to-volume ratio *S/V* = 0.6, being *S* the total external surface.

The boundaries for the calculation of the heating and cooling energy values consist of all the elements separating the conditioned single-zone space from the external environment or unconditioned spaces: external walls and windows. Floors and ceiling are excluded from the envelope representing boundaries with conditioned zones.

The mathematical models adopted to investigate the energy demand of the building are as follows:


The quasi-steady state model includes all sources and sinks of energy, as well as all energy flows through its envelope. The dynamic effects are taken into account by introducing dimensionless utilization factors for heating and cooling [12] that depend on the building inertia by means of the building time constant.

The envelope encloses the volume with a fixed designed temperature for all weather conditions by the use of heating or cooling source energy. Heat flows depend on external and internal influence factors and can be classified as follows:


The amount of energy, which is necessary to maintain the desired room temperature by compensating the excess of losses (*Qtr* and *Qv*) compared to the gains (*Qint* and *Qsol*), is represented by the energy need for heating, *Q <sup>H</sup>*, normalized by the corresponding useful area. To achieve a remarkable reduction in energy need, especially in colder climate zone, renewable energy technologies should be implemented and integrated in the building [14, 15].

Finally, the hourly dynamic model is based on the ISO 52016 [12, 13] in which building elements are modeled by means of lumped parameters. It is worth noting that adopting dynamic models in performing energy analysis, both in

**61**

**Figure 2.**

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

design of new buildings and in rehabilitation of existing buildings, can reduce

By following the definition given in the European Standard EN ISO 10211:2017, thermal bridges are part of the building envelope where the otherwise uniform thermal resistance is significantly changed by full or partial penetration of the building envelope by materials with a different thermal conductivity, or a change in thickness of the fabric, or a difference between internal and external areas, such as occurring at wall, floor, and ceiling junctions. They can contribute to increase the energy demand during heating and cooling seasons and can create interior surface condensation problems. Thermal bridges can be classified as follows [11]: (i) repeating thermal bridges, occurring with a regular pattern; (ii) nonrepeating thermal bridges, such as the bridging of a cavity wall by a single lintel; (iii) geometrical thermal bridges, placed at the junction of two planes. Some examples of thermal bridges in building envelopes are corners that provide additional heat flow paths, window sills, floor to wall junctions, balcony supports, lintels, gaps in insulation,

Thermal bridges produce an additional heat loss affecting the energy balance. It is accounted for by means of the linear thermal transmittance, *ψ*, that is, the rate of heat flow per temperature degree difference per unit length of the junction. In order to reduce heat transmission losses, numerical investigations have been carried out introducing a thermal barrier with different size. In the present chapter, a polystyrene coat of variable size has been added and the effects of thermal insulation have been numerically investigated by using a 2D finite element numerical model.

Structural modeling was defined according to a nonlinear macromodeling approach in the OpenSees [16] framework. At both ends of each structural member, a bending moment-rotation (M-δ) relationship was defined by adopting the Ibarra, Medina, and Krawinkler model [17] (**Figure 2**), whose backbone parameters were

For members having brittle failure, the M-δ relationship was appropriately modified according to the Sezen model [19] in order to account for a lower

evaluated according to Haselton and Deierlein [18].

*Adopted backbone curve for structural members (from Ibarra et al. [17]).*

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

the energy demands for HVAC systems.

*2.1.1 The effects of thermal bridges*

and debris in wall cavity.

**2.2 Seismic modeling**

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

design of new buildings and in rehabilitation of existing buildings, can reduce the energy demands for HVAC systems.

## *2.1.1 The effects of thermal bridges*

*Green Energy Advances*

building are as follows:

exchange rate;

The mathematical models adopted to investigate the energy demand of the

1.the simplified monthly quasi-steady state method based on the European Standard ISO 13790 and the UNI 11300:2014, calculating the seasonal energy balance of the building (time interval depending on the climate zone) [11];

2.the hourly dynamic approach based on the recent European Standard ISO 52016 in which a more complex (with respect to the ISO 13790:2008) and an extensive lumped model adopting a resistance-capacitance (RC) network to

The quasi-steady state model includes all sources and sinks of energy, as well as all energy flows through its envelope. The dynamic effects are taken into account by introducing dimensionless utilization factors for heating and cooling [12] that

The envelope encloses the volume with a fixed designed temperature for all weather conditions by the use of heating or cooling source energy. Heat flows depend on external and internal influence factors and can be classified as follows:

• transmission losses, *Qtr*, which flow through the building envelope from inside

• ventilation losses, *Qv*, caused by exchange of warm indoor air with colder outdoor air through joints by infiltration or exfiltration, respectively. In addition, room air can be exchanged through open windows or by a mechanical ventilation system. Ventilation is indispensable to assure the hygienically necessary air

• solar gains, *Qsol*, due to the irradiation of solar energy through windows and other transparent or translucent constructional elements. Also added to the solar gains, it is that part of the solar heating of the opaque building envelope, from which the indoor area benefits. Solar heat sources result from the solar radiation normally available in the locality concerned, the orientation of the collecting areas, the permanent shading, the solar transmittance and absorp-

• internal gains, *Qint*, represented by the heat released by persons, appliances, computers and other electric devices, as well as from illumination (metabolic heat from occupants and dissipated heat from appliances, dissipated heat from lighting devices, heat dissipated from or absorbed by hot and mains water and sewage systems, heat dissipated from or absorbed by heating, cooling and

The amount of energy, which is necessary to maintain the desired room temperature by compensating the excess of losses (*Qtr* and *Qv*) compared to the gains (*Qint* and *Qsol*), is represented by the energy need for heating, *Q <sup>H</sup>*, normalized by the corresponding useful area. To achieve a remarkable reduction in energy need, especially in colder climate zone, renewable energy technologies should be imple-

Finally, the hourly dynamic model is based on the ISO 52016 [12, 13] in which

building elements are modeled by means of lumped parameters. It is worth noting that adopting dynamic models in performing energy analysis, both in

tion, and thermal heat transfer characteristics of collecting areas;

ventilation systems, heat from or to processes and goods).

mented and integrated in the building [14, 15].

perform the hourly calculation is considered [12, 13].

to outside by conduction or heat transfer;

depend on the building inertia by means of the building time constant.

**60**

By following the definition given in the European Standard EN ISO 10211:2017, thermal bridges are part of the building envelope where the otherwise uniform thermal resistance is significantly changed by full or partial penetration of the building envelope by materials with a different thermal conductivity, or a change in thickness of the fabric, or a difference between internal and external areas, such as occurring at wall, floor, and ceiling junctions. They can contribute to increase the energy demand during heating and cooling seasons and can create interior surface condensation problems. Thermal bridges can be classified as follows [11]: (i) repeating thermal bridges, occurring with a regular pattern; (ii) nonrepeating thermal bridges, such as the bridging of a cavity wall by a single lintel; (iii) geometrical thermal bridges, placed at the junction of two planes. Some examples of thermal bridges in building envelopes are corners that provide additional heat flow paths, window sills, floor to wall junctions, balcony supports, lintels, gaps in insulation, and debris in wall cavity.

Thermal bridges produce an additional heat loss affecting the energy balance. It is accounted for by means of the linear thermal transmittance, *ψ*, that is, the rate of heat flow per temperature degree difference per unit length of the junction. In order to reduce heat transmission losses, numerical investigations have been carried out introducing a thermal barrier with different size. In the present chapter, a polystyrene coat of variable size has been added and the effects of thermal insulation have been numerically investigated by using a 2D finite element numerical model.

#### **2.2 Seismic modeling**

Structural modeling was defined according to a nonlinear macromodeling approach in the OpenSees [16] framework. At both ends of each structural member, a bending moment-rotation (M-δ) relationship was defined by adopting the Ibarra, Medina, and Krawinkler model [17] (**Figure 2**), whose backbone parameters were evaluated according to Haselton and Deierlein [18].

For members having brittle failure, the M-δ relationship was appropriately modified according to the Sezen model [19] in order to account for a lower

**Figure 2.** *Adopted backbone curve for structural members (from Ibarra et al. [17]).*

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 evaluating the structural capacity.

In the different configurations considered in the study, infill panels were modeled by using a nonlinear equivalent diagonal strut according to the Bertoldi model [21].

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