Seismic behavior of existing reinforced concrete frames and its seismic upgrading using energy dissipation devices
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Oliver Saiz, ElenaEditorial
Universidad de Granada
Director
Benavent Climent, AmadeoDepartamento
Universidad de Granada. Departamento de Mecánica de Estructuras e Ingeniería HidráulicaMateria
Hormigón armado Terremotos Efectos de los terremotos Ingeniería sísmica Energía Disipación
Materia UDC
517 624 330506 330525
Date
2016Fecha lectura
2015-09-29Referencia bibliográfica
Oliver Saiz, E. Seismic behavior of existing reinforced concrete frames and its seismic upgrading using energy dissipation devices. Granada: Universidad de Granada, 2016. [http://hdl.handle.net/10481/40942]
Sponsorship
Tesis Univ. Granada. Departamento de Mecánica de Estructuras e Ingeniería Hidráulica; This Thesis received financial support from the Spanish Government under a FPU fellowship of the Ministerio de Educacion, Spain (AP2009-0533).Abstract
Earthquake engineering has progressed significantly in the last few
decades. However, a high proportion of the building stock located in
earthquake-prone regions still exhibits serious seismic deficiencies. In
fact, many of these buildings were designed before the appearance of
seismic codes, in view of rudimentary anti-seismic design criteria
and/or by using obsolete seismic hazard maps. A significant number
of the structures that still remain under-designed have reinforced
concrete (RC) frames as the main system of lateral resistance. Recent
seismic events revealed the poor performance of under-designed RC
frame structures (L’Aquila 2009, Lorca 2011 and Emilia 2012),
accentuating the need for seismic assessment and retrofitting. In this
sense, it is necessary to develop retrofitting strategies that increase
the seismic capacity of existing structures and that control the level
of structural and non-structural damage, within the framework of
performance-based seismic design. To this end, the addition of energy
dissipation devices is an effective technique that provides not only the
strength and deformation capacity required to protect human life, but
also the supplemental energy dissipation capacity necessary to reduce structural and non-structural damage. Among the different types of
energy dissipation devices that are commercially available or under
development, the so-called “hysteretic” dampers are particularly
popular because of their low cost, in comparison with viscous fluid
dampers or viscoelastic solid dampers. For this reason, the use of
brace-type hysteretic dampers for the seismic upgrading of existing
frames has increased exponentially in the past two decades.
Nevertheless, adding hysteretic dampers to an under-designed RC
frame structure is not straightforward and some important issues
must be addressed. On one hand, the connection of the hysteretic
dampers to the existing frame requires special attention. The brace
may develop high axial loads and the design of the anchoring system
to the existing beam-column joint may be costly and difficult to
execute. On the other hand, the dampers require the frame to have a
minimum lateral deformation capacity, in order to develop their
inherent energy dissipation capacity. Under-designed RC frames may
not posses this minimum deformation capacity required for an
efficient combination of frame and dampers. For this reasons, this
Thesis is focused on investigating two main issues: (i) a solution for
connecting brace-type hysteretic dampers to the existing RC frame;
and (ii) a hybrid retrofitting solution with hysteretic dampers that
considers the possibility of including local strengthening procedures
(e.g. FRP/SRP), in order to increase the lateral deformation capacity
of the main frame. Regarding the first issue, a new solution for connecting concentric
braces to beam-column joints of existing RC frames is investigated in
Chapter 3. This solution is suitable for connecting either a
conventional concentric steel brace or a brace-type hysteretic damper.
It consists of (i) two shear-key steel plates fixed to the concrete with
anchor bolts —which restrain the displacements of the end-plates of
the steel brace— and (ii) a device for minimizing friction forces
between the shear-key plates and the end-plates. Minimizing friction
produces the effect of eliminating tension forces on the anchor bolts
and of reducing the bending moments on the shear-key plates.
Consequently, this solution allows using thin plates without stiffeners
and avoids brittle failure modes on the anchors, thus reducing the
number of anchors, as well as the required effective anchorage depth.
To clarify the influence of some parameters (such as the initial gaps
between the steel plates and the thickness of the Teflon sheets) a 3D
finite element model is developed. As a result, execution provisions
and design criteria of the brace-frame connection are proposed.
Finally, the efficiency and validity of the proposed brace-frame
connection is evaluated through shaking-table tests conducted on a
3x3x3 m3 scaled RC frame retrofitted with brace-type hysteretic
dampers. Experimental results show that the braces installed with the
proposed brace-frame connection successfully controlled the damage
on the main frame and that the hysteretic dampers dissipated most of
the energy input by the earthquake. Thus, the proposed brace-frame connection was effective in mobilizing the energy dissipation capacity
of the hysteretic dampers.