Seismic Vulnerability Assessment of a Masonry Building Cluster in Casentino, Italy

Valentina Putrino*, Professor Dina F. D’Ayala*** MSc Student, Earthquake Engineering with Disaster Management** Professor of Structural Engineering, Head of Structure, Department of Civil, Environmental and Geomatic Engineering

Figure 1: 3D view of the damage-characterised masonry building cluster

• Assess the seismic vulnerability of a masonry building cluster located inCasentino, Italy by using an analytical approach called FaMIVE [1].

• Identify the failure mechanisms of each facade in the building compound andcompare the results with a recent qualitative study conducted on the samecluster [2].

• Identify the main parameters controlling the extent of vulnerability.

1- Characterisation of the building compound (shown in Figure 1), e.g. structural, geometrical and mechanical properties.

2- Modelling all facades using the FaMIVE procedure, and obtain the collapse loadfactors corresponding to the failure mechanisms of each facade. The collapsemechanism of each facade is identified based on possible modes listed in Figure 2.3- Evaluate the seismic performance of the masonry compound to a given scenario,by developing the capacity curves and performance points of each façade, followingthe procedure in Figure 3. Consequently, fragility curves are obtained, for eachdamage state.

Figure 3: Flow-chart of FaMIVE procedure

4- Multivariate regression analysis is pursued in order to obtain a mathematicalcorrelation between the independent variables (listed below) and collapse loadfactor (the dependent variable):• Connection at the edge of the facade (1 side, or 2 sides)• Anchorages (ties, wall plates, ring beams, one sided or both sided)• Quoins (one side or both sides)• Number of free corner of the structural unit (zero, one, two)• Quality of masonry condition (good, medium, bad)

Failure mechanisms identified foreach facade are shown in Figure 4 in aplan view. The mechanism found foreach facade is validated using theactual damage collected from an in-situ damage survey. An example ofvalidation is shown in Figure 5 for themost severely damaged facade.

The building cluster is also analysed for various chronological phases,presented in Figure 6. The vulnerability of all phases is further investigatedfor the condition in which no restraining elements, e.g. ties, are in place. Theaverage capacity curve of each phase (obtained by calculating the average ofall facades) is presented in Figure 7, with and without restraints. Resultantfragility curves for phase 6, for both restrain conditions, are shown andcompared in Figure 7.

Figure 4: Failure mechanisms of each facade

Figure 5: Validation of FaMIVE result with the observed damage in facade US4#South

Motivation Masonry Buildings are highly vulnerable in earthquakes.Assessing the seismic vulnerability is essential!

Research Objectives

Methodology

What analytical method is the best for this aim?

Results & Discussions

Figure 2: Possible modes of damage of a facade

Conclusions References

• The failure mechanisms are found and shown to be in a good agreement with theon site damage survey.

• Capacity and fragility curves for with and without restraints cases are derived,showing that the global vulnerability is sensitive to the level of restraints applied.

• Parameters that mostly affect the extent of seismic vulnerability are: i) the level ofanchorage, and ii) the number of free corners present in the building cluster.

Figure 6: Chronological phases of the analysed building cluster

Figure 7: Capacity curves (left) and fragility curves (right) for with and without restraints cases

The importance rate of eachindependent variable is presented inTable 1. The number of free corners isthe most influential factor affecting thevalue of the collapse load factor.A mathematical formulation with aspecific value corresponding to each oneof the parameters involved is also foundas a result of this regression analysis.

Parameter Importance

Connection one edge -

Connection both edges -

Anchorage one side *

Anchorage both side **

Anchorage both side + central **

One lateral quoin -

Two lateral quoins **

Quality of masonry condition **

Number of free corner ***

[1] D. F. D'Ayala. Force and displacement based vulnerability assessment for traditional buildings. Bulletin of Earthquake Engineering, 3(3):235-265, 2005.[2] C. F. Carocci. Small centres damaged by 2009 L’Aquila earthquake: on site analyses of historical masonry aggregates. Bulletin of Earthquake Engineering, 10(1):45-71, 2012.

Table 1: Independent variables