ANALYSIS OF THE EFFECTS FROM LOCAL INTERVENTIONS ON THE
GLOBAL BEHAVIOUR OF MONOLITHIC RC BEAM-COLUMN
STRUCTURES UNDER RETROFITTING AND STRENGTHENING
PhD Thesis Abstract
author of the thesis:
ENG. TANYA IVANOVA CHARDAKOVA
scientific advisor:
PROF. MARINA TRAYKOVA, PHD
MOTIVATION AND ACTUALITY OF THE PROBLEM. AIM AND SCOPES OF THE THESIS.
The problems of the retrofitting and strengthening of existing structures are getting
more and more important worldwide each year, due to the development of the state of the art,
the increasing demands for the built environment, the sustainability issues, etc.
In Bulgaria one of the most popular types of structures of existing buildings is the
monolithic reinforced concrete beam-column one. Many of these structures are designed in
accordance with older standards or are not designed at all.
Very often, mainly for economical reasons, the strengthening of the structure or parts of
it aims improvement of the bearing capacity for gravity loads only, while seismic and other
actions are out of the scope of the project. Also in the common practice local strengthening of
individual structural elements is often needed, but full global retrofitting or strengthening is
not possible or does not make economical sense. In such cases it is necessary to know what
would be the effect of the local intervention on the global behaviour of the structure - whether
its influence is positive or negative and the extend of the influence.
The existing standards in Bulgaria, concerning existing structures, are mainly focused
on the effects from seismic action, while the common gravity loads are not discussed.
Because of these reasons this thesis aims to evaluate qualitatively and quantitatively the
influence of different local interventions on the global behaviour of monolithic RC beamcolumn structures under retrofitting and strengthening. For this purpose the most important
factors, that can influence the global behaviour of such structures are analysed first. Based on
the conclusions from this analysis, series of numerical experiments on finite element models
of typical monolithic RC beam-column structures are carried trough. The results are compared
and based on the analysis of the results, some recommendations for simplified practical
procedures are formulated, by which the effects of local interventions on the global capacity
of monolithic RC beam-column structures can be accounted for.
OUTLINE OF THE THESIS.
The thesis consist of introduction, four chapters and conclusion.
In the Introduction the motivation and actuality of the problem is described. The aim
and scope of the thesis is defined.
In Chapter One a general state-of-the-art report is presented. The main topics that are
considered are:
Why and when a structure should be retrofitted or strengthened;
Assessment and monitoring of existing buildings;
Standards and other documents, concerning existing structures;
Methods and techniques for the retrofitting and strengthening of existing
monolithic RC beam-column structures.
At the end of the chapter it is concluded that no specific information on the subject is
found. The goal and tasks of the thesis are defined.
Chapter Two is focused on the modeling of monolithic RC beam-column structures and
the validation of the model techniques that are to be used in the thesis. First the most
important factors, that can influence the global behaviour of such structures are analysed. A
review of the types of numerical models is presented, including some proposals for models,
accounting for the initial preloading of the existing structure. The different approaches for the
modeling of compared by numerical examples. Finally, the modeling approach to be used is
defined and validated, using existing experimental data.
Chapter Three is the major part of the thesis, where the series of numerical experiments
on finite element models of typical monolithic RC beam-column structures, that are carried
through are described. The considered structures are:
one-storey, one-span structure;
one-storey, two-span structure;
three-storey, two-span structure;
three-storey, multiple span structure.
The local interventions that are considered are strengthening of slabs, beams or columns
by reinforced concrete or by FRP. Also in some of the models removal of infill masonry is
considered.
The global behaviour of the structure is assessed:
for the gravity loads - deformation factor, defined in the thesis;
for lateral load - nonlinear static analysis;
for the dynamic properties of the structure - modal analysis.
In the models the following important factors are considered: nonlinearity of the
materials, cracking and crushing of the concrete, reinforcement ratio, initial preloading of the
existing structure, influence of the infills, etc.
In Chapter Four the results, obtained in Chapter Three are analysed. Some general
conclusions are done and are recommended some simplified practical procedures are
formulated, by which the effects of local interventions on the global capacity of monolithic
RC beam-column structures can be accounted for. The field for future work is outlined.
In the Conclusion the need of more sophisticated standards for the existing structure is
stressed. The original contributions of the thesis are summarised.