1. Introduction

2. The RI.P.R.O.VA.RE. Project: Goals, Methodology, Results

3. The Proposed Procedure

3.1. Seismic Risk Assessment and Mitigation

The designed procedure here reported aims to supply a set of practical solutions and a simplified approach to make “inland areas” less prone to seismic events, by increasing their resilience. The developed method can be summarized in four distinct phases: 1) Assessment of the seismic hazard [14,15] of the considered areas; 2) Evaluation of the seismic exposure [14,15] of the zone of interest; 3) Estimation of the seismic vulnerability [14,15] of each part of the focus area; 4) Intervention planning by considering the guidelines annexed to Italian Ministry of the Environment and Protection of Land and Sea Decree n. 65 07/03/2017 [20] to reduce the overall seismic risk.

A seismic risk mitigation policy requires the identification and knowledge of the main factors that can describe the hazard, vulnerabilities and exposure affecting the areas;. however, the identification and knowledge may have different meanings as the scale of the survey changes, since the need to arrive at risk scenarios in an acceptable time in a context of often limited resources and knowledge, focuses on the need for flexible, modular, and scalable analytical methodologies and procedures.

In this context, so-called expeditive methodologies for analysis at different scales have been developed, starting from the seismic event of Irpinia (Italy). In the national context, as regards the assessment of the seismic risk to the ordinary building, it is possible to refer to the guidelines adopted by the Tuscany Region (L.R. 65/2014) [14,15] which are based on a multi-scale (multi-level) methodology, that can be considered very useful for quickly classifying risks in large areas. The Tuscan approach [14,15] considers 3 levels of analysis (Regional, Municipal, Urban), each of which uses data generally already available; the methodology returns to each scale comparable risk indices.

The Regional scale analysis (Level 0 - L0) assumes the municipalities as a reference field and considers the following factors:

• Seismic hazard: basic hazard of each town [16];
• Exposure: weighted averages of population and building factors obtained from ISTAT data [17];
• Vulnerability: evolution of the building development in relation to the history of the seismic classification of the considered Municipality and the data available from the Civil Protection Department updated to 31st January 2020 [18].

At Municipal scale (Level 1 - L1), the analysis is conducted with reference to the scope of the census area, using the same methodology as Level 0. Finally, the analysis of risk scenarios at the Urban scale (Level 2 - L2) focuses on the study of detailed aspects in consideration of the built-up fabric intrinsic characteristics.

3.1.1. Seismic Hazard

Seismic hazard is defined as the probability that an earthquake equal or greater than a certain threshold of intensity, magnitude, or peak ground acceleration (PGA) will occur in a certain area and time interval.

At Level 0 (L0), the Hazard Class is described by the basic hazard of each Municipality in terms of peak ground horizontal acceleration (Ag), with return period of 475 years (part 3.2 of the NTC 2018 [19]). The aforementioned accelerations (Hazard Values - VP), evaluated in the centroid of each Town, allow to define the Hazard Index (IP) [14].

At Level 1 (L1), the Hazard Class is evaluated in each census section considering the peak ground acceleration (PGA) in the centroid of the considered section (Table 1 of [15]).

At Level 2 (L2), the Hazard Class is rather evaluated considering also the effects induced by local site conditions through a Local Hazard Index (I_ploc) (Table 2 of [15]).

This index can be evaluated based on the information reported in the Seismic Microzonation Maps elaborated by the Municipalities. In summary, the Local Hazard Index refers to the following effects:

• Very high local seismic hazard (S.4)
• High local seismic hazard (S.3)
• Medium local seismic hazard (S.2)
• Low local seismic hazard (S.1).

The Seismic Hazard Class (P₂) is thus obtained, for Level L2, from the combination of the Base Hazard Class (P) and the Local Hazard Index [15]:

IP = P + I_ploc

(1)

Table 3. Hazard classes, values, and indices at Level 2 (Table 3 of [15]).

Table 3. Hazard classes, values, and indices at Level 2 (Table 3 of [15]).

Hazard Class	IP Value	Seismic Hazard (P2)
High	IP > 6	4
Medium - High	IP = 5	3
Medium - Low	IP = 4	2
Low	IP ≤ 3	1

3.1.2. Seismic Vulnerability

The vulnerability describes the propensity of the building to damage for seismic events defined by predetermined intensity thresholds.

At regional scale (L0) buildings are divided into 3 classes:

• Historic buildings
• Contemporary buildings
• Modern buildings

Basing on this classification, the Vulnerability Values index (VV) is then computed as the ratio between the number of the most vulnerable buildings (MV) and the total of those built between 1946 and 2005.

The most vulnerable buildings (MV) are those that have potential deficiencies because they were built before the seismic classification of the territory, or in the absence of seismic technical standards. In any case, the highest class is assigned to the buildings built before 1962.

Based on the Vulnerability Values, a Vulnerability Class and Vulnerability Index (IV) are assigned as follows:

Table 4. Vulnerability classes, values, and indices at Level 0 (Table 3 of [14]).

Table 4. Vulnerability classes, values, and indices at Level 0 (Table 3 of [14]).

	Vulnerability Class	Vulnerability Value (VP)	IV
4	High	0.65 ≤ VV ≤ 1 in seismic area 2	5
3	Medium - High	VV < 0.65 in seismic area 2	4
2	Medium - Low	VV = 1 in seismic area 3	3
1	Low	VV < 1 in seismic area 3VV ≤ 1 in seismic area 4	3

At Municipal Scale (L1), the Vulnerability Index is evaluated by explicitly considering the construction period, the structural typology, and the height of the building:

• Period of construction: for each census section an average period value is calculated [15]:

Vperiod = (∑N_buiding × K_e)/N_buiding,tot)

(2)

where N_buiding is the number of buildings for each construction period in the homogeneous area, K_e is the period coefficient taken from Table 5 in [15] and N_buiding,tot the total number of buildings in the homogeneous area [15]; finally, an Index of epoch (I_period) is associated to each value of epoch (V_period), following Table 6 in [15].

• Structural typology: the ratio of buildings in reinforced concrete to the total of buildings for each census section, setting the threshold of 75% and defined in Table 7 of [15].
• Height of buildings:

V_height = (∑N_buiding × K_p)/N_buiding,tot

(3)

where this time N_buiding is the number of buildings with the same number of floors, K_p the floor coefficient taken from Table 8 of [15] and N_buiding,tot the total number of buildings of the census section [15]. The Height index will be 1 for V_height > 0.500 or 0 for V_height ≤ 0.500 (Table 9 in [15]).

Table 7. Exposure classes, values, and indices at Level 1 (Table 16 of [15]).

Table 7. Exposure classes, values, and indices at Level 1 (Table 16 of [15]).

Seismic Exposure	IEs	E
High	IEs ≥ 4	4
Medium - High	IEs = 3	3
Medium - Low	IEs = 2	2
Low	IEs = 1	1

• Interaction between buildings: an urban density indicator (I_d) is defined based on the geographical location of buildings (Table 10 of [15]).
• Intended use: a large light construction type index (I_u) is defined based on the macro-intended use (Table 10 in [15]).
• Seismic classification: a classification index (I_c) is defined in Table 11 of [15].

The Vulnerability Class (V) for each census section is therefore defined with the determination of the Vulnerability Index (I_v), given by the sum of the computed indices [15]:

I_v = I_e + (I_t + I_a + I_u + I_d + I_c)

(4)

Thus, the seismic vulnerability class (V) is defined as follows:

Regarding the seismic vulnerability of urban centres (Level 2), aimed at the implementation or updating of urban planning tools, in addition to the assessments of Level 1, it is possible to refer also to the results of any analysis and detailed studies on homogeneous areas, identified as municipal or sub-municipal areas (compartments). These evaluations are aimed at both the validation of the statistical and synthetic results of Level 1, as well as at the description with greater accuracy and detail of the building or urban vulnerability.

3.1.3. Seismic Exposure

The seismic exposure describes the quality and quantity of the goods exposed that could suffer damage during an earthquake and may involve in economic losses and/or victims.

On a Regional Scale (L0), seismic exposure is assessed based on the Exposure Value (VE) obtained from the combination of the population (N_pop) and the number of buildings (N_building) present in each Municipality [15]:

VE = 2/3 N_pop + 1/3 N_building

(5)

Based on the calculated values, the Exposure Index (IE) is defined [15]:

At Municipal level (L1), exposure is assessed on the basis of population, buildings and intended use, as follows:

• Exposed population: it is assessed by the density index (I_density), considering the average of the resident population and the number of total buildings in relation to the area expressed in weighted hectares:

I_density = (2/3 N_pop + 1/3 N_building)/Area

(6)

where N_pop is total resident population by homogeneous area, N_building the total number of buildings [15].

• Intended use: it is evaluated considering the location of the construction and assigning a relative coefficient (I_destination) (Table 15 of [15]).

The Exposure Class (E) is then defined using an Exposure Indicator (IEs), computed as follow [15]:

IEs = I_density + I_destination

(7)

At Urban level (L2) seismic exposure is assessed for each census area using the same approach as for the municipal level (L1) unless detailed studies are available.

3.1.4. Seismic Risk Assessment

The seismic risk represents an estimate of the expected losses in a certain period of time and is a function of the hazard, vulnerability, and exposure.

At the Regional level (L0) the Risk Class is defined considering the Risk Index (IR), evaluated as the contribution of the Hazard, Vulnerability and Exposure Indices:

IR = IP + IE + IV

(8)

where IP, IE and IV are danger, exposure, and vulnerability index respectively [14,15].

At the Municipal level (L1) the seismic risk class is assessed considering a Risk Index (IR), computed as a function of Hazard (P), Vulnerability (V) and Exposure (E) [15]:

IR = P + V + E

(9)

Finally, the assessment of the seismic risk at the Urban scale (L2) is conducted, considering the same factors evaluated with a Level 2 deepening.

3.1.5. Strategies to Support Seismic Risk Reduction Policies

The guidelines annexed to Ministerial Decree n.65 07/03/2017 [20] introduce a new method of classification that is based on 8 classes of Risk, with increasing risk from letter A+ to letter G. The determination of this class can be carried out according to two alternative methods: the conventional method and the simplified method.

In the case of the assessment of the risk class for masonry constructions with the simplified method, the above guidelines refer substantially to the vulnerability class defined by the European Macroseismic Scale (EMS).

This approach can be complemented by the Level L1 analyses described above; in this regard, it is necessary to normalize the description of the Risk Classes and Vulnerabilities respectively as follows:

The simplified procedure described in the guidelines attached to DM 65/2017 [20] identifies 7 types of masonry, assigning for each of them the corresponding class of vulnerability (Figure 2 of [20]).

The assessment of the vulnerability class, which is fundamental for the identification of the risk class, is therefore based on the following factors (Table 4 of [20]):

• the structural typology of the buildings under consideration;
• negative characteristics which may cause deviation from the typical average class of the structural typology [20].

For the assignment of the risk class, the guidelines consider the seismic classification of the territory, in accordance with the provisions of the O.P.C.M. 3274 of 20/03/2003 and subsequent amendments and additions [21].

Table 12. PAM class assigned according to the vulnerability class assigned to the building and the seismic zone in which it is located (Table 5 of [20]).

Table 12. PAM class assigned according to the vulnerability class assigned to the building and the seismic zone in which it is located (Table 5 of [20]).

Risk Class	PAM	Zone 1	Zone 2	Zone 3	Zone 4
A+*	PAM ≤ 0.5%				V1 – V2
A*	0.5 < PAM ≤ 1.0%			V1 – V2	V3 – V4
B*	1.0 < PAM ≤ 1.5%	V1	V1 – V2	V3	V5
C*	1.5 < PAM ≤ 2.5%	V2	V3	V4	V6
D*	2.5 < PAM ≤ 3.5%	V3	V4	V5 – V6
E*	3.5 < PAM ≤ 4.5%	V4	V5
F*	4.5 < PAM ≤ 7.5%	V5	V6
G*	PAM ≥ 7.5%	V6

In order to implement a seismic risk mitigation strategy in a large area, it is possible to refer to widespread local strengthening interventions, such as those described in [20].

For what regards masonry structures, a list of possible interventions is reported in Table 6 of [20], thanks to which the assessment of the transition of the vulnerability class following the local strengthening interventions, the obtainable improvements on the risk and, therefore, to evaluate the positive effects of individual intervention strategies.

For productive activities buildings, in agreement with [20], there is the chance to consider valid the transition to the immediately higher Risk Class by performing only local strengthening interventions, even in the absence of a prior assignment of the Risk Class, if the requirements listed in it for the elimination of their deficiencies are met.

Finally, in the case of reinforced concrete buildings, as in the case of structures similar to industrial buildings (productive activities buildings), it is possible to consider the transition to the next higher Risk Class as valid, performing only local strengthening interventions and even in the absence of a prior assignment of the Risk Class. This is possible if the structure was originally designed with frames in both directions and if all of operations listed in [20] are performed.

Assuming a large-scale risk mitigation policy, it is therefore possible to identify the improvement that can be achieved in the areas under investigation with targeted interventions based on the types of construction present according to [20].

4. Demonstrative Application and Results

5. Conclusion

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