Assessing the seismic vulnerability of masonry buildings - Seismic Risk Analysis and Management of Civil Infrastructure Systems - page 335

developed for vulnerability assessment at territorial scale. For this reason
procedures aimed at the assessment of single buildings are not included.
The choice of the most suitable procedure is highly dependent on the
resources available for the data collection, the computational expertise
available, and ultimately the scale and aim of the study. Empirical proce-
dures can be used for fairly large-scale studies to defi ne damage scenarios;
however, if the purpose of the study is to identify within a district or urban
centre specifi c buildings in need of strengthening, so as to increase their
seismic resistance, then a suitable analytical procedure should be
preferred.
13.3 Collapse-mechanismapproachtoseismic
vulnerability of masonry buildings
In defi ning a capacity spectrum-based approach for masonry structures, the
major diffi culty is in devising a procedure suffi ciently 'open' or 'fl exible' to
accommodate the variability in construction typical of masonry building.
Such variability relates to geometry, material and structural parameters, and
results in a relatively large number of possible failure modes; these factors
should be considered for a realistic assessment of the vulnerability of a
building population.
D'Ayala (2005) has proposed a version of FaMIVE that uses the collapse
mechanism approach to derive capacity curves, directly related to the failure
modes of a building. The post-elastic displacement is quantifi ed in terms of
simple stability considerations and bilinear pushover curves are obtained.
Considering that performance assessment in terms of expected displace-
ment better represents the post-elastic behaviour of the building, the
approach has been implemented by defi ning limit displacement conditions
and compares these values to displacement demands obtained through
inelastic displacement spectra. Since the mechanical approach allows us to
evaluate the capacity of the structure as an analytical function with a small
number of geometrical and mechanical parameters, it is possible to apply a
suitable procedure for the uncertainty propagation to distinctly quantify
the uncertainties associated both with the 'capacity' (model error, param-
eter uncertainties, uncertainties on damage states) and with the 'demand'
(seismic input uncertainty). In the following, uncertainties associated with
the model and the capacity curves are further discussed.
Based on the evidence collected from post-earthquake site surveys,
D'Ayala et al. (2008) have identifi ed a suite of 12 possible modes of failure,
as shown in Fig. 13.1. Each mode of failure corresponds to different con-
straints between the façade and the rest of the structure, hence a collapse
mechanism can be univocally defi ned and its collapse load multiplier
computed.