Abstract
This
paper presents overview of the recent developments in the shear wall design in
order to enhance the seismic performance and its suitability for retrofitting.
The approach is to combine different advantages of materials into a composite
shear wall so that it endures the earthquake/fire with minimum damage. The different
approaches have shown that the composite shear wall is definitely the better
option in terms of seismic performance, sustainability as well as post disaster
retrofitting. The innovative methods are promising however they still needs to
be modified as scope and size of structures is increasing every day.
Keywords:
Shear wall, seismic, composite shear wall, FRP, GFRP, CFRP, CFST
Shear walls are a widely used lateral load
resisting system in structures,
and frequent earthquakes have highlighted the importance of the performance of
shear walls during seismic events. Shear walls finds its
application from a building to the seashore structures. As the purpose of use
is different, they are subjected to various kinds of external forces and
conditions. A shear wall can fail in flexure, shear, flexure-shear, sliding
shear, or out-of-plane, depending on the geometric configurations and material
properties, it has been found that lack of ductile detailing reason behind most
of the failure.
There has been an increase in the number
of tall buildings, for commercial and residential purposes, under construction
throughout the world. This increase has illuminated the necessity for knowledge
of the behavior of these structures, and, in particular, the necessity for
producing methods of analysis capable of giving rapid and accurate assessments
of their overall strength and stiffness. As buildings increase in height, it
becomes important to ensure adequate lateral stiffness to resist loads that
might arise because of wind, seismic, or blast effects. This stiffness might be
achieved in various ways. In framed structures, it might be obtained by bracing
members, by the rigidity of the joints, by complete shear truss assemblies
acting in conjunction with the frame, or by infilling the frame with shear
resistant panels. A simplification of the latter is shear wall construction, in
which the relatively high in-plane stiffness of the walls, external and
internal, is employed to resist the lateral forces.
Experimental studies showed that concrete
shear walls reinforced exclusively with GFRP bars had satisfactory strength and
stable cyclic behavior, making them suitable for use in areas with low seismic
risk.
Recent studies have shown that the
innovative shear walls detailed with a type of self-centering reinforcement and
fiber reinforced concrete are effective in reducing the permanent displacement
and concrete damage compared to conventional concrete (RC) shear walls.
However, more investigation is required into the seismic design parameters,
such as the inelastic rotational capacity and plastic hinge length of
innovative shear walls.
In the traditional design philosophy of
structures, seismic loads are reduced in accordance with the ductility level of
the lateral load resisting system used in a structure. In the performance-based
seismic design (PBSD) of building structures, the structural and non-structural
elements of buildings are required to satisfy targeted building performance
levels for given levels of seismic hazard, according to FEMA 356. For instance,
for a given earthquake with a specific return period, a building structure is
required to satisfy certain levels of performance, such as immediate occupancy
(IO), life safety (LS), and collapse prevention (CP). Traditionally, targeted
building performance levels for a building structure are based on the damage
levels that the structural and non-structural members of the building have
sustained. In addition, the PBSD allows the owners of structures to define
further performance objectives, such as self-centering, to lower the
probability of future rehabilitation or reconstruction.
Figure 1
DfD connections in shear wall
Figure 2 Masonary
Shear wall
Figure 3
RC walls with steel–concrete composite boundary elements
2. Literature
review:
As a part of literature review an adequate
amount of research articles were studied and few of them were finally chosen to
be included in this.
(Ren et al., 2018) proposed a
new form of a composite shear wall consisting of a reinforced concrete (RC)
wall web and two boundary columns, in the form of square concrete-filled steel
tubes (CFST) incorporating a carbon fiber–reinforced polymer (CFRP)–confined
concrete core. To evaluate its seismic performance, the
proposed shear wall was tested under constant axial compression force and
lateral cyclic loading. Three additional shear walls with different boundary
column configurations were also tested: (i) an ordinary shear wall, (ii) a
shear wall with CFST boundary columns, and (iii) a shear wall with double-skin
CFST boundary columns. The failure mode, load-bearing capacity, ductility,
energy dissipation capacity, stiffness degradation, strength de- gradation, and
deformation mode of the four shear walls were thoroughly examined and compared.
(Epackachi &
Whittaker, 2018) used LS-DYNA
to simulate the in-plane cyclic behavior of lightly reinforced, low-aspect
ratio reinforced concrete (RC) shear walls. The
validated LS-DYNA model was used in a parametric study to
investigate the effects of wall aspect ratio, reinforcement ratios in web and
boundary ele- ments, and compressive axial load on the monotonic response of RC
walls.
(Ni & Birely, 2018) used a potential
multi-hazard scenario for buildings is the sequential occurrence of fire and
earthquakes, with such a scenario possible if a fire is triggered by an initial
seismic event and a subsequent aftershock occurs. With fire negatively
influencing the stiffness, strength, and deformation capacity of structural
components, the building may be at risk for local or global collapse. The key
role of reinforced concrete (RC) walls as lateral load resisting components
make them of particular importance in considering the post-fire earthquake
performance of buildings.
(R. Ding et al., 2018) proposed
a new mixed beam-shell model for the seismic analysis of reinforced concrete
coupled walls with sufficient efficiency and accuracy on the platform of
general finite element software MSC.Marc. Boundary elements at the ends of wall
piers were simulated by conventional fiber
beam-column elements, while the web of the wall pier was
modeled by the layered shell element. Coupling beams were
simulated by non-conventional fiber beam-column elements, which can not only
take into account the shear and shear-sliding deformation together with various
failure modes of conventionally reinforced beams, but also the shear and rebar
slip deformation of diagonally reinforced beams. RBE2 link elements were
utilized to connect the coupling beams to the wall piers. Eight test specimens
reported in the literature were used to validate the proposed model.
(Ghazizadeh et al.,
2018) in his study developed a finite-element (FE) analysis model for
hybrid GFRP-steel reinforced shear walls for moderate seismic demands. The
steel lent ductility to the system, while the GFRP material enhanced the
self-centering ability of the wall to reduce permanent displacements. The analysis
model was first validated with experimental results obtained from steel- and
FRP-reinforced walls from literature, and then used to determine the most
suitable hybrid scheme combining ease of construction, maximum ductility, and
minimum residual displacements.
(Kolozvari et al., 2019) used five
conceptually-different state-of-the-art finite element models for RC walls,
including models based on either a fixed-crack or a rotating-crack approach for
simulating the biaxial behavior of concrete under plane-stress state, models
characterized with either a single- or a multi-layered representation of the
wall cross-section, and models with or without consideration of various
individual failure mechanisms (e.g., buckling of reinforcement, out-of-plane
instability). Modeling approaches were validated against experimental data
obtained for five benchmark RC wall specimens, all with rectangular
cross-sections, yet are differentiated by a range of salient response
characteristics (e.g., aspect ratio, axial load, failure mechanism), in order
to assess the capabilities of the models in representing the response of
isolated planar walls under uni-directional lateral loading, as well as to
identify future research directions.
(Bypour et al., 2019) proposed four connection types and numerically investigated to transfer
the tension field forces between SPSW and RC frame (RCF). Three types of
connections are applicable for re- habilitating of existing RC structures and
one type can be used for new construction. The behavior of connections were
evaluated using non-linear finite element analysis (NLFEA).
(Ghazizadeh et al.,
2019) developed a
finite-element analysis model to conduct a com- prehensive parametric study on
hybrid GFRP-steel reinforced shear walls. First, the validated model was
used to address some other design aspects of tested specimens such as presence
of axial load and arrangement of GFRP bars. Next, the reliability of the
section analysis based on CSA A23.3-14 code for design of conventional and
hybrid squat walls are investigated. The self-centering and economic aspects of
design of hybrid GFRP-steel reinforced walls were
also addressed. Using the analysis model, a promising structural application of
SFRC (steel fiber-reinforced concrete) shear walls was
also proposed.
(Honarparast &
Chaallal, 2019) modelled two 20-story
CSWs located in Western seismic Canadian zone. One CSW was designed according
to old National Building Code of Canada (NBCC) 1941 and the other one designed
in conformity with modern NBCC 2015 and Canadian Standard Association (CSA)
A23.3-14. The nonlinear time-history analyses of the two types of CSWs as well
as the CFRP retrofitted one under simulated earthquake motions were carried out
using RUAUMOKO program to: (i) evaluate the seismic performance of old
designed CSWs and highlight their deficiencies by comparing its response with
that of corresponding modern design CSWs; and (ii) evaluate the effectiveness
of EB- Carbon FRP (EB-CFRP) retrofitting on the seismic response of deficient
CSWs.
(Momeni & Dolatshahi, 2019) used an extensive database on the images of damaged
rectangular reinforced concrete shear walls collected from literature. This
database included more than 200 images from experimental
quasi-static cyclic tests. Using the concept of fractal geometry, several
probabilistic models were developed by extracting and regenerating the
surface crack patterns of the collected walls. Those models could estimate the
peak drift ratio that the structure experienced. The peak drift ratio predicted
by the proposed models of this paper can be used to calculate the probability
of exceedance of different damage states using existing fragility models.
Furthermore, new fragility models were directly developed using the images of the
damaged walls of the collected database. The proposed fragility curves calculate
the probability of exceedance of damage states using the crack pattern of the
damaged shear walls and consequently provide an estimation of the loss, repair
cost, and repair time of the walls.
(Sakr et al., 2019) numerically analyzed the behavior of strengthened
RC shear walls by a UHPFRC and reinforced UHPFRC (R-UHPFRC) jacketing under
lateral loading using a two- dimensional (2D) model and the bond stress-slip
model was incorporated to the analysis to simulate the inter- facial
concrete-to-concrete bond. First, behavior of RC and UHPFRC shear walls
subjected to lateral loading was investigated using the proposed 2D model.
Validation of the model was done using the available experimental results.
The validated model was utilized to study the behavior of RC shear walls
strengthened by UHPFRC and R- UHPFRC jacketing under lateral loading.
(Aly & Galal, 2019) assessed (i.e. numerically) the seismic performance and
collapse capacity of ductile RM buildings, having heights exceeding the code
limit, built using ductile RM shear walls with boundary elements as the SFRS. The
main objective was to propose height limits based on solid and
objective seismic performance acceptance criteria. In this regard, six
archetype buildings with varying heights were designed according to CSA S304-14 with ductile
RM structural walls having confined boundary elements. The reference buildings were located in
two regions representing the high and moderate seismicity levels of NBCC-15.
The seismic performance was evaluated using nonlinear pseudo- static pushover
and Incremental Dynamic Analyses (IDA).
(Seif ElDin et al., 2019) analysed previously reported test results of eight RM
shear-dominated fully-grouted rectangular squat walls subjected to cyclic
lateral excitations to evaluate the FBD and DBD parameters. The main variables
of the tested walls were the level of axial compressive stress, vertical
and horizontal reinforcement ratio, anchorage end detail, and the spacing of
horizontal and vertical reinforcement.
(Q. Zhang et al., 2019) investigated the seismic performance of seawater sea-sand
concrete (SSC) shear wall reinforced with glass fiber reinforced plastic (GFRP)
bars. Three shear wall specimens were designed for the seismic performance
evaluation, including natural aggregate concrete (NAC) reinforced with steel
bars (SNW), NAC reinforced with GFRP bars (GNW) and SSC reinforced with GFRP
bars (GSW).
(T. Ding et al., 2020) carried out an experimental
study to investigate the seismic behavior of newly developed concrete shear
walls with the bolted end-plate design for deconstruction (DfD) connections,
with the aim of applying reused structural components to mid-rise buildings.
This DfD connection was characterized by pre-buried end-plates and welding shear
studs. The proper design was proposed to facilitate the application for future
deconstruction and reconstruction. Four concrete shear walls with different
aspect ratios were designed and tested according to a cyclic loading test to
evaluate the seismic behavior. The principle of reuse and recycle were firstly
both applied to concrete structures in the domain of this research.
(He et al., 2020) conducted shake table tests on two concrete shear wall model
structures, together with the tests of complete uniaxial compressive
constitutive curves of concrete, were carried out. The purpose of the tests was to provide
quantitative benchmark results for the verification and improvement of refined
multi-scale numerical simulation method for structures exhibiting strong
non-linear behaviors. Three important properties were carefully taken into account
in the tests, including: (1) The scale ratio should not be too small so that
detailed local damage could be revealed and the experimental results could
serve as benchmark data; (2) The model structures should exhibit strong
nonlinear behaviors but the accumulated damage between load cases should be
avoided; (3) Concrete specimens should be simultaneously tested to capture the
complete stress-strain curves rather than only the two parameters (the
compressive strength and Young’s modulus); and (4) The unavoidable randomness
involved in concrete structures should be quantified.
(J. Zhang et al., 2020) proposed an innovative shear wall, which was composed of
high-strength concrete and steel rebars, as well as concrete-encased CFST
columns embedded at boundary elements. To study the cyclic and resilient
behavior of the proposed wall, four walls with shear span ratios of 2.2 were
designed and tested under quasi-static cyclic loads. The test parameters were
the type of longitudinal bars at boundary elements, the presence of steel
fibers, and the axial compression ratio.
(Mangalathu et al., 2020) studied recent advances in the area of machine learning to
determine the failure mode of shear walls as a function of geometric
configurations, material properties, and reinforcement details. His study assembled a
comprehensive database consisting of 393 experimental results for shear walls
with various geometric configurations. Eight machine learning models, including
Naïve Bayes, K-Nearest Neighbors, Decision Tree, Random Forest, AdaBoost,
XGBoost, LightGBM, and CatBoost were evaluated in his study, in
order to establish the best prediction model.
(Tolou Kian & Cruz-Noguez,
2020) investigates
the response of three innovative walls cast with fiber-reinforced composites
and reinforced with steel rebars and a type of self-centering reinforcement
consisting of shape memory alloy (SMA) bars, glass fiber reinforced polymer (GFRP)
bars, or high-strength steel strands. The response of each innovative wall was
compared to that of a conventional RC shear wall called the control wall. Then,
the inelastic rotational capacity, plastic hinge length, and self-centering of
the innovative walls were discussed within the framework of the
seismic design codes of North America.
3. Discussion
and Consclusion:
Through
these years the innovation in material science and its nascent application has spearheaded
improvement of the performance of shear wall during earthquake, fire and post
retrofitting period. The basic problem is still to achieve the stability within
a feasible limit of expenditure of resources. As we are being able to build
better shear walls, the scope and size of application into the civil engineering
structures has also increased. The new shear walls like composite shear wall, CFST
shear wall, and new reinforcing methods like using FRP, CFRP, GFRP for the reinforcement
(hybrid reinforcement) has shown promising results. The analytical model has
been well developed to imitate and predict the behaviour of the experimental ones.
Furthermore, there has been research on predicting the damage just by analysing
the surface cracks with the use of the concept of fractal geometry. On the top of that, new methods have
been invented to quickly retrofit the shear wall after the disaster. Below are
the conclusions that can be drawn from the papers:
1.
Compared
with the ordinary shear wall (RC-W), the cracking load, yielding load,
load-bearing capacity (maximum load), deformation capacity, ductility, and
energy dissipation capacity of the proposed composite shear wall（composite shear wall with CFST
incorporating CFRP-confined concrete cores as boundary elements） are significantly improved (all
> 20%); in particular, the load carrying capacity and deformation capacity
are increased by 44.1% and 62.4%, respectively.
2.
As
for the proposed composite shear walls incorporating steel fiber reinforced HSC
and CFST boundary elements within the limit of axial compression ratio
specified in GB50011-2010, the residual deformation after unloading was small
until an approximate loading drift of 2%. After that, the hysteresis curves
tended to be full and the energy dissipation capacity increased. These results
show the proposed composite shear walls have potential to exhibit reparability
after major earthquakes and collapse-resistance capacity when suffered from strong
earthquakes.
3.
Adding
steel fibers to concrete matrix could effectively reduce the damage degree and
improve the deformation capacity of the proposed composite walls, which was
helpful for making full use of the performance advantages of high-strength bars
and concrete.
4.
The
permanent drift ratios can be reduced using innovative method self-centering reinforcing
along with FRP.
5.
GFRP
is promising and offers the same structural integrity as normal reinforcement while
it is far more ecofriendly and sustainable.
6.
Hybrid system (*GFRP-reinforced and hybrid GFRP-steel
reinforced shear walls) was effective to minimize the residual displacements
under strong ground motions.
7.
Seawater
sea-sand concrete shear wall reinforced with GFRP
bars is a better option than a normal RC shear wall for costal structures as
the later one is unsustainable due to its massive consumption of natural
resources and deterioration of the environment.
8.
DfD connections to connect two shear wall seems to be a
promising option as its seismic performance is reasonably good and also it can help
use reuse of shear wall.
9.
The models and methods we have currently are quite efficient
in predicting the behavior of the shear wall during these disasters.
10.
Predicting
damage based on the external appearance and correlation other parameters is
still a big challenge.
11.
For
the multi-hazard case, we need to use a lot of modifier to predict the seismic behavior
of a structure after fire or earthquake. This needs to be investigated a lot as
at time of disaster it is a quite common phenomenon.
12.
Data
driven machine learning based approach can be used in future to predict damage
of shear wall.
4.
References
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