Abstract—The experimental research presented in this paper
aims to investigate the cut-out effect on the behavior of the
precast reinforced concrete wall panels under in-plane seismic
loading conditions. Wall openings in buildings are provided for
architectural reasons or access requirements, while the cut-outs in
walls are made due to change of use or simply, architectural
reasons. The precast reinforced concrete wall panel presented in
this paper was designed according to the 1981 Romanian code, and
has an initial small window opening. In order to investigate the
cut-out effect, the small window opening was enlarged to a wide
window opening. The specimen was first tested in the unstrengthened
condition and subsequently was repaired using high strength mortar,
rehabilitated, and then tested again. The experimental tests are
described and a discussion based on cut-out effect on shear walls
is undertaken and future research is suggested. Numerical analysis
are further needed in order to simulate the cut-out interventions
made in precast reinforced concrete shear walls of different
parameters.
I. INTRODUCTION ETWEEN the 1950s and 1970s, the use of large
panel
structures was widely used, but then after followed the decay
period until the 1990s, which marked the end in Romania. It is
known that the system composed of precast reinforced concrete
panels can provide a good seismic performance, but after 50 years
of existence and interventions some were subjected to, detailed
investigation is strongly needed. The investigated experimental
specimens meet the requirements of Eurocode 8 for walls designed to
medium ductility and are referred as large lightly reinforced
walls.
The application of textile reinforced mortar (TRM) was investigated
in this study as a rehabilitation manner, in order to restore the
load bearing capacity of the specimen first tested in the
unstrengthened condition. Research on textile reinforced
This work was supported in part by the Grant no. 3-002/2011,
INSPIRE –
Integrated Strategies and Policy Instruments for Retrofitting
buildings to reduce primary energy use and GHG emissions, Project
type PN II ERA NET, financed by the Executive Agency for Higher
Education, Research, Development and Innovation Funding (UEFISCDI),
Romania.
C. Todut is with the Politehnica University Timisoara, 300223,
Romania (phone: 0040-256-403-950; fax: 0040-256-403-958; e-mail:
carla.todut@ student.upt.ro).
D. Dan is with the Politehnica University Timisoara, 300223,
Romania (e- mail:
[email protected]).
V. Stoian is with the Politehnica University Timisoara, 300223,
Romania (e-mail:
[email protected]).
mortar strenghtening were conducted by Bernat-Maso et al. [1],
Triantafillou and Papanicolaou [2], Papanicolau et al. [3],
San-José et al. [4], Bernat et al. [5], Elsanadedy et al. [6],
Larrinaga et al. [7]. Other research presented by Mohammed et al.
[8], Bing Li and Qin Chen [9], Mosoarca [10], Kitano et al. [11],
Demeter et al. [12], Sas et al. [13], Doh and Fragomeni [14], Guan
et al. [15], Carrillo and Alcocer [16], investigated reinforced
concrete walls with openings. An experimental research on the
effect of cut-out made in wall panels to the behavior of the
reinforced concrete wall panel was investigated. The tests were
performed under in-plane cyclic lateral loads. The specimen was
tested unstrengthened, then after it was repaired, rehabilitated
and tested again. A few literature on the TRM for RC wall
strengthening and cut-outs made in walls is available.
The paper aims to comprehend the influence of the wall cut- out on
the seismic performance of the wall without cut-out, and also the
performance of the TRM system for the load bearing capacity
restoration. Important aspects related to the seismic performance,
lateral stiffness, horizontal displacement (drift), ductility and
energy dissipation capacity are presented and discussed for the
rehabilitated element in comparison with the reference one. The
behavior of the tested elements also include: the failure modes,
the strain analysis in reinforcement and glass fiber grid (TRM
component). Some remarks are also presented for the TRM anchorage
system used.
II. EXPERIMENTAL PROGRAM The experimental program consists of six
1:1.2 scale
elements, namely precast reinforced concrete wall panels PRCWP
(7–12), designed and casted according to a Romanian Project Type
770-81 [17], [18]. Two specimens were selected for investigation in
this paper, namely PRCWP (10-L1/L3-T), specimen having an initial
small window opening and enlarged to a wide window opening, and
PRCWP (11-L1-T), specimen having a small window opening. On the
basis of the two experimental tests in the unstrengthened
condition, important aspects related to the cut-out effect can be
drawn out. Then after the specimen with cut-out opening was
repaired using high strength mortar, rehabilitated and subsequently
tested again, to investigate the strengthening effect and the
seismic behavior efficiency. The post-damage strengthened specimen
was denoted PRCWP (10-L1/L3-T/R). The experimental specimens were:
2150 mm height, 2750 mm
TRM strengthening of precast reinforced concrete wall panel with
cut-out opening -
experimental investigation C. Todut, D. Dan, and V. Stoian
B
ISBN: 978-1-61804-241-5 110
width and 100 mm thickness. The small window opening was 1000 mm
height and 750 mm length, while after enlargement the dimensions of
the wide window opening were 1000 mm height and 1750 mm length. The
wall panels were set between two reinforced steel concrete
composite beams, namely a loading beam and a foundation beam. The
reinforcement of the precast reinforced concrete (RC) wall panel
was made of: horizontal and vertical bars, welded wire mesh in both
piers, spatial reinforcement cage in the spandrel, an inclined bar
at each corner of the opening, a vertical bar each side of the
opening on its height and a wire mesh in the parapet. The
configuration of the two specimens selected for the cut-out
investigation is presented in Figure 1 (a) and (b).
Figure 1 the schematics and reinforcement details of the
specimens
Table 1 material properties of steel
Table 2 Geometrical and mechanical properties of the grid
A. Material Considerations The specimen’s concrete quality was
C16/20 class, the
reinforcement S255 for the spatial reinforcement cage, S355 for
horizontal, vertical and inclined steel bars, and S490 for the
steel wire mesh. The steel reinforcement properties obtained
experimentally are given in Table 1. Textile reinforced mortar was
used for the rehabilitation of the specimen. The system used was
made of glass fiber grid and 1-component, fiber reinforced
cementitious mortar with a compressive strength at 7 days of 15
N/mm2 according to the product data sheet. Table 2 summarizes the
geometrical and mechanical properties of the grid used. The
mentioned characteristics are based on manufacturer’s data. The
mortar, used to replace the heavily damaged concrete, was Sika
MonoTop 614, with a compressive strength at 28 days of 55– 60
N/mm2, according to the product data sheet.
B. Behavior and results of unstrengthened elements Similar behavior
was observed for the two unstrengthened
specimens. Cracks appeared in the spandrel, piers, wings, corners
of the window opening, cast in place mortar and mostly in the
parapet. Failure of the tested specimens are presented in Figure 2
(a) [19] and (b) [20]. The first diagonal crack in the right pier
appeared at 0.3% drift ratio, first cycle, loaded from the right
for both specimens. Concrete crushing was observed in the left
corners of the specimen with window enlargement, while for the
specimen with small opening at the bottom left corner of the
opening and parapet. Failure of the PRCWP (10-L1/L3-T) was attained
at 0.65% drift ratio, while for the PRCWP (11-L1-T) it was recorded
at 0.73% drift ratio.
C. Repair and strengthening of the specimen The rehabilitation
strategy adopted here intended to restore
the initial load bearing capacity of the element, namely PRCWP
(10-L1/L3-T/R), the solution being qualitative and based on the
behavior of the reference specimen.
The PRCWP (10-L1/L3-T/R) specimen, having an initial narrow window
opening and enlarged to a wide window opening, was repaired after
the experimental test of the reference specimen using a repair
mortar (Sika MonoTop 614) and then it was rehabilitated using TRM
with GF grid and subsequently tested again. After the repair of the
specimen, the rehabilitation process started with surface
preparation, namely wall panel polishing, 8 mm hole drilling for
the anchorage system, 20 mm rounding of the window edges and
vacuum- cleaning. Then, the anchorage system composed of threaded
rods having 6 cm length were fixed to the panel using resin, in
order to provide a mechanical and punctual type of anchoring system
(together with the nut and washer) for the transmission of stresses
and deformations from the structure substrate to the TRM system.
According to the rehabilitation strategy (Figure
21 50
Ø10, S255
Ø10, S255
Ø10, S255
Ø10, S255
14 395 584 206
8 424 553
16 385 613
207 8 425 507 205
OB37 S255 6 400 550 Re-bar type Grade Φ (mm) fy (N/mm2) fu (N/mm2)
Es (N/mm2)
Elongation at break
Component Areal weight [g/m2]
ISBN: 978-1-61804-241-5 111
3), the GF grid was cut using scissors. A bonding primer, namely
Sika Monotop 910 N was applied on the surface of the wall, followed
by the first layer of mortar, GF grid and the second layer of
mortar (Figure 4). Related to the glass fiber grid application
(Figure 5), first were mounted the number 4 grid pieces, each side
of the parapet,
Figure 2 Failure of the tested unstrengthened specimens
Figure 3 The TRM rehabilitation strategy for the wall with
cut-out
Figure 4 Rehabilitation detail for the TRM use
Figure 5 Glass fiber grid application for the wall with
cut-out
followed by the number 5 grid pieces, wrapped around the parapet,
over the number 4 grid pieces. Then the number two grid pieces were
placed each side of the parapet, followed by the number 3 grid
pieces which were wrapped over the number 2 grid pieces, each side
of the opening. Finally the number 1 glass fiber grid piece was
wrapped around the spandrel. Strain gauges were mounted on rebar
for the reference element and on the GF grid for the strengthened
one.
D. Testing methodology and test set-up Detailed data related to the
tests set up and testing
methodology of the precast reinforced concrete wall panel specimens
are presented in Demeter [21]. A general view of the test set-up is
presented in Figure 6.
The testing procedure of the specimens consisted in quasi- static
reversed cyclic lateral loads - displacement controlled (using two
cycles per drift), having the measure of 0.1% drift ratio, namely
2.15 mm. Vertical loading was also applied to simulate the gravity
loading condition and restrain the rotation of the elements.
Pressure transducers (P), displacement transducers (D) and strain
gauges placed on rebars and glass fiber grid (G) were used to
monitor the behavior of the precast reinforced concrete wall panel
specimens (Figure 7). The same displacement transducer position was
used for all the experimental specimens.
1 - 1 piece
2 pieces
12 2
3 3
glass fiber grid application
ISBN: 978-1-61804-241-5 112
Figure 7 Instrumentation layout of the specimens
Figure 8 Failure details of the TRM strengthened specimen
III. EXPERIMENTAL RESULTS AND COMPARATIVE STUDY
A. General Behavior and Failure Modes of the TRM post- damage
strengthened specimen
The behavior of the strengthened and retested specimen
LA TE
RAL R
EA CT.
F RAM
1910 1080 280 1000 1250 1000 280 1080 1910 9790
D2
G
D1
D3
D1
ISBN: 978-1-61804-241-5 113
PRCWP (10-L1/L3-T/R) under reversed cyclic lateral loads, revealed
an expected behavior in accordance with the design strategy. During
the experimental test, the PRCWP (10-L1/L3- T/R) specimen developed
cracks in the spandrel, piers, corners of the opening and parapet.
The TRM system exhibited mortar detachment from 0.3% drift ratio,
followed by mortar exfoliation and system excessive detachment
(about 3 cm between the TRM system and the wall was observed)
between 0.4-0.6% drift ratio. Subsequent detachments and mortar
crushing appeared between 0.7-0.8% drift ratio. At the end of the
experimental test, the TRM system was removed from each side of the
opening and thick inclined cracks were observed together with
concrete crushing (Figure 8). The load bearing capacity of the
initial system was restored even if the anchorage system used
turned to be inefficient. It can be concluded that the punctual
mechanical type of anchorage is a cheap alternative to the surface
type of anchorage [21] but smaller distances between the threaded
rods are necessary.
B. Load displacement response diagrams The obtained lateral loads
versus the drift ratio envelopes
are presented in Fig. 9a for the cut-out effect investigation and
in Fig. 9b for the TRM performance. It can be seen that significant
strength reduction (≈ 50 %) was induced by the cut-out made in the
experimental specimen. The TRM rehabilitation strategy restored the
initial load bearing capacity of the specimen with cut-out opening,
despite the inefficiency of the anchorage system used.
C. Energy dissipation The cumulative energy dissipation was
obtained by the
continuous integration of the load-drift hysteretic response using
an iterative equation, as presented in [21].
A comparison between the cumulative dissipated energy (CED) per
half-cycle versus drift ratio within each test performed is
presented in Fig. 10. It can be concluded that the PRCWP
(10-L1/L3-T) specimen with cut-out opening developed a significant
lower energy dissipation (≈ 57 %) compared to the reference
specimen, namely PRCWP (11-L1- T). In the case of the post-damage
strengthened specimen using TRM, namely PRCWP (10-L1/L3-T/R), the
energy dissipation was higher (≈ 33 %) compared to the
unstrengthened specimen, PRCWP (10-L1/L3-T).
Figure 9 Load-drift ratio response diagrams
Figure 10 The cumulative energy dissipation of the specimens
(b)
(a)
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D. Strain analysis During the experimental tests, strain was
measured on the
vertical, horizontal and inclined reinforcing bars, and horizontal
on the glass fiber grid. In Figure 11 are presented the strain ε
(‰) versus drift ratio for the current tested specimens. The
position of strain gauges is shown in Fig. 7. It can be seen that,
yielding of the reinforcement was attained for the unstrengthened
wall panels, in the top left corners of the opening and parapet. In
the case of the TRM strengthened specimen, the grid debonded beyond
2 ‰ strain due to the inefficiency of the anchorage system
used.
E. Stiffness degradation According to the stiffness versus drift
ratio diagram (Figure
12), the cut-out made in wall produced a significant reduction in
the initial stiffness (50%) compared to the reference specimen,
PRCWP (11-L1-T). In the case of the wall with cut- out opening the
initial stiffness was similar for the unstregthened and post-damage
strengthened condition.
F. Ductility considerations The ductility of the wall specimens was
evaluated using the
μ0.85 method, which defines the ductility (μ = Δu/Δy) as the ratio
between the ultimate displacement (Δu - the displacement when the
horizontal load falls to 80% of the maximum horizontal force) to
the displacement corresponding to 0.85 of the maximum load on the
ascending branch of the monotonic envelope (Δy - the displacement
at yielding). The ductility coefficient μ0.85 for the tested
specimens is presented in Figure 13. It can be concluded that the
specimen with cut-out opening, namely PRCWP (10-L1/L3-T) exhibited
a lower ductility than the reference one, PRCWP (11-L1-T). The TRM
strengthened specimen, PRCWP (10-L1/L3-T/R), exhibited a
considerable higher ductility than the reference specimen, PRCWP
(10-L1/L3-T).
IV. CONCLUSIONS The work presented in this paper refers to the
experimental
results on cut-out effect investigation and post-damage
strengthening of a precast reinforced concrete wall panel using
textile reinforced mortar.
The following conclusions can be drawn within the limitation of the
current research:
Figure 11 Steel strain (ε) versus drift ratio of the
specimens
Figure 12 The stiffness versus drift ratio diagram of the
specimens
Figure 13 The normalized ductility coefficient for specimens
-3.5 -3
-2.5 -2
-1.5 -1
-0.5 0
0.5 1
1.5 2
2.5 3
3.5
-1.1 -0.9 -0.7 -0.5 -0.3 -0.1 0.1 0.3 0.5 0.7 0.9 1.1
strain ‰
3.5
-1.1 -0.9 -0.7 -0.5 -0.3 -0.1 0.1 0.3 0.5 0.7 0.9 1.1
strain ‰
3.5
-1.1 -0.9 -0.7 -0.5 -0.3 -0.1 0.1 0.3 0.5 0.7 0.9 1.1
strain ‰
ISBN: 978-1-61804-241-5 115
- the corners of the opening and the parapet exhibited concrete
crushing in the case of the reference specimens; - the dissipated
energy was significantly lower for the wall with cut-out compared
to the wall without cut-out, while the post-damage strengthened
specimen dissipated more energy compared to the unstrengthened one;
- according to the μ0.85 method, the ductility of the wall with
cut-out was inferior to the ductility of the wall without cut-out,
while the post-damage strengthened specimen proved to be more
ductile compared to the reference specimen; - vertical wire mesh
yielding was recorded in the parapet for the unstrengthened
specimen; while in the case of the TRM strengthened specimen, the
grid debonded beyond 2 ‰ strain; - the cut-out made in wall
produced a significant reduction in the initial stiffness (50%)
compared to the reference specimen, while the TRM strengthened
specimen exhibited a comparable initial stiffness to the reference
one; - TRM system can be an effective solution for strengthening
elements; the punctual anchorage system used turned to be
inefficient, allowing for system local debondings. Further studies
related to the numerical modelling of the tested elements are in
progress. The studies aims to establish the seismic performance of
PRCWP having different parameters and the most convenient solutions
of strengthening.
ACKNOWLEDGMENT The author acknowledges the following research grant
for
the support of this study: 1. Grant no. 3-002/2011, INSPIRE –
Integrated Strategies and Policy Instruments for Retrofitting
buildings to reduce primary energy use and GHG emissions, Project
type PN II ERA NET, financed by the Executive Agency for Higher
Education, Research, Development and Innovation Funding (UEFISCDI),
Romania.
2. This work was partially supported by the strategic grant
POSDRU/159/1.5/S/137070 (2014) of the Ministry of National
Education, Romania, co-financed by the European Social Fund –
Investing in People, within the Sectoral Operational Programme
Human Resources Development 2007-2013.
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[12] I. Demeter, T. Nagy-György, V. Stoian, D. Dan, “Seismic
Retrofit of Cut-out Weakened Precast RC Walls by Externally Bonded
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[13] G. Sas, I. Demeter, A. Carolin, T. Nagy-György, V. Stoian, B.
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[19] Seismic Strengthening of a Precast Reinforced Concrete Wall
Panel using Textile Reinforced Mortar – Todut C., Stoian V.,
Demeter I., Fofiu M., in Proceedings of the International
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[20] Glass Fiber versus Carbon Fiber Grid used in Textile
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[21] Demeter, I. (2011), Seismic retrofit of precast RC walls by
externally bonded CFRP composites. PhD Thesis, Politehnica
University of Timisoara.
C. Todut was born in Satu Mare, Romania on the 13th of April 1986.
She earned the Bachelor’s degree in Civil Engineering at the
Politehnica University Timisoara, Romania in 2009, the Master of
Science degree in Structures at the Politehnica University
Timisoara, Romania in 2011. Currently she is a PhD Student at the
Civil Engineering Department of the Construction Faculty,
Politehnica University Timisoara, Romania. During Faculty some of
the author’s achievements are obtaining a scholarship at the
University of Edinburgh, Scotland, 3rd place at Carpatcement
contest, 1st place in the County Olympics for the Strength of
Materials contest, Timisoara and 2nd place in the National Olympics
for the Strength of Materials contest, Iasi. Previous publications
of her appear in the Proceedings of fib 2013, FRP RCS 2013 and
Structural Faults and Repair 2012. Her current research is based on
precast reinforced concrete wall panels, seismic performance,
weakening induced by cut-outs and strengthening possibilities. PhD
Student Todut was a student member of the American Concrete
Institute and the American Society of Civil Engineers.
Advances in Engineering Mechanics and Materials
ISBN: 978-1-61804-241-5 116