Proceedings of the International Symposium on Engineering Lessons Learned fromthe 2011 Great East Japan Earthquake, March 1-4, 2012, Tokyo, Japan

EXPERIMENTAL STUDY ON SEISMIC RETROFIT OF
RC COLUMN WITH WING WALL IN TAIWAN AND
JAPANShih-Hsun YIN1, Shuenn-Yih CHANG2, Wen-I LIAO3 and Yu-Chi SUNG4
1,3Associate Professor, Department of Civil Engineering, National Taipei University of Technology
Taipei, Taiwan, shihhsun@ntut.edu.tw, wiliao@ntut.edu.tw
2,4Professor, Department of Civil Engineering, National Taipei University of Technology
Taipei, Taiwan, changsy@ntut.edu.tw, sungyc@ntut.edu.tw

ABSTRACT: In this study, a series of cyclic loading tests were conducted for threefull-scale specimens including an existing column and two columns strengthened withwing walls respectively fabricated using Taiwan’s and Japan’s structural details. The
experimental results show that the existing columns retrofitted with wing wall caneffectively improve seismic strength and that there is no rupture of concrete cover in thebase of the column with wing walls if using Japan’s structural details while the rupture
does occur if using Taiwan’s structural details.
Key Words: Seismic retrofit, column with wing walls.

INTRODUCTION
Many structures which do not meet current seismic code requirements were damaged or even totallycollapse as a result of Taiwan Chi-Chi earthquake. Therefore, seismic evaluation and retrofitting ofexisting vulnerable buildings become urgent matters in Taiwan. It also accelerated the studies aimed toestablish technology for strengthening existing buildings with different strategies including steel
jacketing, RC jacketing, CFRP/GFRP jacketing, and addition of braces, walls, passive energy
dissipating devices, and base isolation. In general, repair and retrofit techniques (ATC-40 1996,FEMA 2000, JBDPA2001) can be used for enhancing the stiffness, the strength, and/or ductility ofbuildings. Many studies indicated that reinforced concrete columns with wing-walls had relatively
good earthquake-resistant performance such as increasing column stiffness and strength in reinforced
concrete buildings and were simple, convenient, economic, and effective (Kabeyasawa 2007 & 2008,Md Nafiur 2007, Tetsuo 2006, Tojo 2008).
The reliable connection between original columns and added wing walls plays a key role on theseismic performance of the retrofitted columns (Moehle 2000). Also, we found that there are
significant differences on reinforcement structural details between Taiwan and Japan in which column
with wing walls are made. In this study, a series of cyclic loading tests were conducted for threefull-scale specimens including an existing column and two columns strengthened with wing walls. The
structural details commonly used in Taiwan and Japan were respectively adopted for fabricating thecolumn with wing walls. Thus, the seismic performance of these specimens can be studied and1282

compared due to different structural details. In addition, seismic evaluations of these specimens wereperformed, and the results obtained were compared to the test results for the confirmation of thefeasibility of the evaluation techniques.

TEST ON COLUMNS WITH WING WALLS
Test specimens
To simulate the column of existing older school buildings which do not meet current seismic code
requirements, the cross section size was chosen as 300mm × 400mm, the D10 ties were spaced at a
distance of 250 mm with unreliable 90o end hooks, and the nominal strength of concrete was 15 MPa.
The configuration and details of the specimen denoted by S1 to simulate the substandard column arepresented in Fig. 1. To enhance column stiffness, strength, and ductility, the original column isstrengthen with wing walls on its both sides. To ensure that the wing walls connected with the column
can work together, rebar doweling is needed. In Taiwan, the rebar doweling to footing, columns, andbeams is used with double layers in practice. In contrast, the rebar doweling with a single layer is usedin Japan. In addition, spiral rebar is placed along the boundaries between the new wing walls and theold footing, columns, and beams to prevent from the split of concrete. Also, the outmost rebars inwing walls from the surface of the original column should be connected to the rebar in the top beamand bottom footing by weld and hook in Japan. It is interesting to investigate the difference in seismic
performance due to different reinforcement details. Therefore, two specimens of the substandard
column retrofitted by wing walls respectively using Taiwan and Japan structural details are designed,and respectively denoted by S4 and S5. Their configuration and details are presented in Fig. 2 and 3.

Fig. 1 The specimen configuration and details of the substandard column (unit: mm)1283

Fig. 2 The specimen configuration and details of the substandard column retrofitted by wing walls
using Taiwan structural details (unit: mm)

Fig. 3 The specimen configuration and details of the substandard column retrofitted by wing walls
using Japan structural details (unit: mm)

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Cyclic loading testFig. 4 shows the experimental apparatus installed at the Architecture and Building Research Institute,
the Ministry of the Interior, Taiwan, which consists of reaction wall, strong floor, and one horizontal
jack with maximum loading capacity of 2000kN. The rigid beam is placed on the top of the column
and two high-strength bars are tensioned to connect to the rigid beam and strong floor such that theaxial load can be applied at the column. The constant axial load applied in the cyclic loading test is247 kN corresponding to 0.15fc’Ag, where Ag is column section area and fc’ is compressive concrete
strength. In addition, the lateral load is applied to the specimen through the horizontal jack andcontrolled based on displacement. The displacement time history of the actuator for cyclic loading as
shown in Fig. 5 is specified in the control unit.

Fig. 4 Test setup

Fig. 5 The displacement time history of the actuator for cyclic loading

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EXPERIMENTAL RESULTS AND DISCUSSIONS
Fig. 6, 7, and 8 respectively present the hysteretic responses for the substandard column (i.e. S1), thesubstandard column retrofitted by wing walls using Taiwan structural details (i.e. S4), and thesubstandard column retrofitted by wing walls using Japan structural details (i.e. S5). Table 1, 2, and 3summarize the important phenomenon observed during the test of each specimen. In addition, theultimate shear strength for each column is calculated by the evaluation method found in Seismic
Evaluation Standard for RC buildings by The Japan Building Disaster Prevention Association [JBDPA,2001]. The calculated shear strength and the observed shear strength and ductility ratio for eachspecimen are listed in Table 4.
Based on the above results, we found that the substandard column retrofitted by wing walls using
either Taiwan or Japan structural details showed excellent response with an increase in both shear
strength and stiffness. However, the ductility ratio was decreased, which means that the retrofit
columns cannot provide a ductile failure mechanism. Also, hysteretic loops in Fig 7 and 8 are very
similar, which means that the seismic performance of the columns with wing wall is not highly
affected by different structural details. The very important finding about the difference on structural
behavior between S4 and S5 is that there is no rupture of concrete cover in the base of the column withwing wall if using Japan’s structural details while the rupture does occur if using Taiwan’s structuraldetails. This is because that both ends of vertical reinforcing bars near the outmost section of the wing
wall were securely connected to existing stirrups if Japan’s structural details are adopted.

Fig. 6 Load displacement response of the specimen S11286

Fig. 7 Load displacement response of the specimen S4Fig. 8 Load displacement response of the specimen S51287

Table 1 The descriptions of observation during the test of specimen S1Lateraldisplacement (mm)2536

Drift ratio
(%)
1.375
272

490

5Observation
Flexural cracks were initially developed at the bottom of column.
Spalling of cover concrete near the bottom of column occurred.
Massive Spalling of cover concrete and extensive exposure of
reinforcing bars were observed.
Crush of core concrete and buckling of reinforcing bars wereobserved at the bottom of column as shown in Fig. 9.

Table 2 The descriptions of observation during the test of specimen S4Lateraldisplacement (mm)Drift ratio
(%)

20

1.125

22.5

1.25

36

245

2.5

54

372
108

46Observation
Shear cracks were initially developed at the outmost corner ofwing wall.
Narrow cracks occurred on the surface of cover concrete in thefooting.
Spalling of cover concrete and exposure of reinforcing bars wereobserved in the outmost edge of wing wall.
Severe damages were observed in the bottom of wing wall andcover concrete of the footing as shown in Fig. 10.
Rebar dowels in the bottom of wing wall were pulled out, anddamage in the cover concrete of the footing occurred extensively.
Wing walls lost their shear resistanceReinforcing bars of the original column buckled.

Table 3 The descriptions of observation during the test of specimen S5Lateraldisplacement (mm)Drift ratio
(%)

20

1.125

22.5

1.25

36

245

2.5

54

372

4108

6

Observation
Shear cracks were initially developed at the outmost corner ofwing wall.
No cracks occurred on the surface of cover concrete in thefooting.
Spalling of cover concrete and exposure of reinforcing bars wereobserved in the outmost edge of wing wall.
Severe damages were observed in the bottom of wing wall, but
minor damage occurred in the cover concrete of the footing.
Rebar dowels in the bottom of wing wall buckled, and shear
cracks at the bottom of column were developed very quickly.
Wing walls lost their shear resistanceReinforcing bars of the original column buckled, and crush ofcore concrete at the bottom was observed as shown in Fig. 11.

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Table 4 Comparison of calculated and observed shear strengths and ductility ratio

The original column
S1

The original column withwing walls using Taiwan
structural details
S4

The original column withwing walls using Japan
structural details
S5

104.03 (kN)

389.91 (kN)

377.04 (kN)

135.28 (kN)

317.65 (kN)

317.65 (kN)

( JBDPA, 2001)
Ultimate
displacement

77.24 (mm)35.68 (mm)36.04 (mm)Yielddisplacement

26.9 (mm)18.02 (mm)18.05 (mm)

2.87

1.98

2.00

Ultimate shear
strength

Qexperiment
Ultimate shear
strengthQsu∆u∆yDuctility ratioµ∆ = ∆u / ∆yFig. 9 Final failure state of the specimen S1 when the drift ratio reaches to 5%1289

Fig. 10 Damage state of the footing of the specimen S4 when the drift ratio reaches to 2.5%

Fig. 11 Final failure state of the specimen S5 when the drift ratio reaches to 6%

CONCLUSIONSThis study focused on experimental testing for seismic retrofit of RC column with wing walls
respectively fabricated using Taiwan’s and Japan’s structural details. The experimental results show1290

that the existing columns retrofitted with wing walls can effectively improve seismic strength foreither using Taiwan’s structural details or Japan’s structural details. It seems that the seismic
performance of the columns with wing walls is not highly affected by different structural details sincevery similar hysteretic loops were obtained from the cyclic loading tests. It is interesting to find that
there is no rupture of concrete cover in the base of the column with wing walls if using Japan’s
structural details while the rupture does occur if using Taiwan’s structural details. This is because thatboth ends of vertical reinforcing bars near the outmost section of the wing wall were securely
connected to existing stirrups if Japan’s structural details are adopted.

ACKNOWLEDGMENTS
The authors wish to acknowledge the Architecture and Building Research Institute, the Ministry of theInterior, Taiwan and the National Science Council, Taiwan for the generous support of this work.

REFERENCES
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