Civil Engineering Association

Seismic vulnerability of reinforced concrete structure

The assessment of seismic vulnerability of the existing building stock plays a
key role in the development of instruments aimed at the evaluation and the
mitigation of seismic risk. The investigation of seismic vulnerability of existing
Reinforced Concrete (RC) buildings is of fundamental importance since this
building typology represents a large part of the existing building stock in many
areas subjected to high seismic risk; moreover, the seismic behaviour of these
buildings is often affected by deficiencies due to the absence of compliance
with the modern earthquake engineering design principles or, even, to the
absence of a seismic design.
In this thesis, the seismic vulnerability of existing RC buildings is
investigated from different points of view.
First, an overview of literature methods is carried out, illustrating main
empirical and analytical approaches to large scale vulnerability assessment
(Chapter I).
Hence, in Chapter II the seismic behaviour of existing RC buildings is
investigated through experimental and numerical activities focused on the
deformation capacity of substandard RC members, with emphasis on members
with smooth bars. To this aim, code and literature formulations for the
evaluation of deformation capacity of RC members are illustrated and
discussed; then, based on experimental data, a new proposal for the assessment
of deformation capacity of columns with smooth bars is presented. Then, bond
between steel and concrete for this kind of reinforcement is investigated
through an experimental study and the formulation of an analytical model based
on the obtained data. The influence of the absence of proper transverse
reinforcement details is experimentally investigated, too. Finally, the so-called fixed-end rotation mechanism is studied by means of a two-component
numerical model representing a RC element model, including the anchorage
element.
Capacity models for shear-controlled members and for beam-column joints
are briefly reported and discussed, too.
The seismic behaviour of existing RC buildings is also investigated through
an analysis of observed damage to RC buildings in L’Aquila after the 6th April
2009 earthquake.
Seismic behaviour of RC buildings is also strongly influenced by the
presence of infill walls, as highlighted by earthquake damage observation. In
Chapter III, this issue is illustrated through a discussion of local and global
interaction mechanisms between the RC structure and infill elements. Then, an
analytical investigation of the influence of these elements on the elastic period
of vibration of RC buildings is carried out, leading to the formulation of
simplified expressions, which are compared with empirical and numerical data
from literature.
The influence of infills on the seismic capacity of RC buildings has been
widely investigated in literature by different authors. In Chapter IV, these
studies are presented first. Hence, the seismic capacity of a case study Gravity
Load Designed building with different infill configurations (bare, uniformly
infilled or “pilotis”) is investigated by means of Static Push-Over analyses, thus
highlighting through a sensitivity analysis the influence of main material and
capacity parameters on the seismic capacity of the studied building at different
Limit States. A relative comparison is carried out, also by means of fragility
curves, to analyze the influence of different infill arrangements on the seismic
behaviour.
Finally, a seismic capacity assessment of the case study building is carried
out on simplified models based on a Shear Type assumption. Results obtained
from “exact” and simplified models are compared and discussed.
In Chapter V, a procedure is proposed for the simplified seismic
vulnerability assessment of existing RC buildings, based on the described Shear Type assumption. The proposed method employs few data – such as number of
storeys, global dimensions and type of design – to define the structural model
by means of a simulated design procedure. Nonlinear static response of the
structural model, including infill elements, is characterized, and pushover
analysis is carried out in closed-form. Fragility curves and corresponding failure
probability at different Limit States are calculated, once seismic hazard has
been defined. Finally, the proposed method is applied to the Avellino city
(southern Italy), employing data about building stock from a field survey,
including structural typology, global building dimensions and age of
construction. Obtained results show the influence of main characteristics, such
as the number of storeys and type of design, on the seismic vulnerability of the
building stock.