Effects of Haunch on the Beam-Column Joint of Soft
First-Story in RC Building
T. Ogawa, M. Teshigawara & A. Nakamura
Nagoya University, Nagoya, Japan
S. Takahashi, G. Kotani, T. Kawai & T. Ichinose
Nagoya Institute of Technology, Nagoya, Japan
T. Kamiya, T. Taguchi, W. Kohira & T. Umeno
Yahagi Construction Co., Ltd., Nagoya, Japan
H. Fukuyama
Building Research Institue, Tsukuba, Japan
H. Suwada & T. Kabeyasawa
National Institute for Land and Infrastructure, Tsukuba, Japan
N. Hanai
Kyushu Sangyo University, Fukuoka, Japan
SUMMARY
There are many damage reports about the soft-story construction against earthquakes. Therefore, four
specimens consisting of members only around the beam-column joint of soft first-story are constructed
and loaded to failure by statically cyclic load simulating earthquake to obtain fundamental data. In
opening direction loading, all the specimens showed flexural failure of first-story column. In closing
direction loading, the specimens in which the first-story column is extended toward inside show
flexural failure of first-story column, whereas the specimens in which the first-story column is
extended toward outside showed joint failure. The stiffness and the strength of the specimens with
haunches are larger than those of the specimens without haunches. A set of new design equations to
estimate the flexural and joint strength are proposed based on the observed failure modes, considering
the effect of haunch and position of critical section.
Keywords: soft first-story, Beam-column joints, anchorage, haunch
1. INTRODUCTION
There are many damage reports about the soft-story construction against earthquakes. The first story in
a multi-story apartment building is expected to use for parking lot or commercial space. In these
buildings, shear walls with boundary columns are used as partition wall in the upper stories whereas
the first-story is single-bay moment resisting frame. Once an earthquake would occur, deformation of
the structure is concentrated to the soft first-story. Therefore, the building is in danger of causing story
collapse.
anchorage failure
wall
the second-story
column
beam
modeling portion
the first-story
column
Figure 1.1. The typical beam-column joint at the soft first-story
In order to present from the soft first-story collapse, the stiffness and the strength of the first-story are
increased by making the depths of the first-story columns much larger than those of upper stories (See
Fig 1.1). But it is hard to transfer the moment of the top of the first-story column to the beam and the
second-story column well due to the discontinuous of column. In addition, unexpected failure mode
might cause, for example, shear failure on a beam-column joint and anchorage failure (G. Kotani., et
al, 2011). In this study, tests are conducted to clear the force transfer mechanism and to avoid such
failures.
2. TEST SPECIMEN AND MATERIAL
Four specimens I-1t, I-ht, O-1t and O-ht consisting of members only around the joint illustrated in Fig.
1.1 are tested. Scale of the specimens is one half. The specimens are upside-down for the convenience
of the loading. The general shape and re-bars arrangement of I-ht and O-ht is shown in Fig. 2.1. The
test parameters are as follows: (1) extension direction of the first-story column, outside (O-1t, O-ht) or
inside (I-1t, I-ht), and (2) with/ without haunch at the corner of the joint.
axial force
opening
2st-story
column
wall
500
1000
250
250
(a) specimen I-ht
+
250
14
B
b
A
66
00
1st-story
column
5
beam
600
beam
opening
C
450
5
66
250
-
2st-story
column
wall
500
1000
450
250
1st-story
column
450
0
140
250
closing
+
C
B
b
A
450
250
-
250
600
250
closing
axial force
250
(b) specimen O-ht
Figure 2.1. The general shape and re-bars arrangement of Test specimens, I-ht and O-ht
2.1. Detail of I-1t, I-ht specimens
The specimens I-1t and I-ht are constructed with the reinforcing arrangement shown in Figure 2.2 (a),
(b). The discontinuous first-story column re-bars are anchored into beam-column joint with 180
degrees hook. The anchorage length from the face of the column joint is satisfied with the AIJ
Guideline [1]. The beam re-bars are anchored into beam-column joint with 90 degrees hook. The
anchorage length from the face of the beam joint is also satisfied with the AIJ Guideline [1]. The
specimen I-ht is provided with haunch in which five reinforcement (blue reinforcement in Fig. 2.2 (b))
inclined 30 degrees are set at the corner of the joint. The inclined reinforcements are anchored into
column with 180 degrees hook and into beam on straight anchorage.
2.2. Detail of O-1t, O-ht specimens
The specimen O-1t and O-ht was constructed with the reinforcing arrangement shown in Figure 2.2 (c),
(d). The discontinuous first-story column re-bars are anchored into beam-column joint with 180
degrees hook. The anchorage length from the face of the column joint is satisfied with the AIJ
100 36
36 100
114
36 100
2-story column
36 89
114 114
500
hoops
5-D6＠40
（0.80%）
18-D19
（2.07%）
114
140
500
140
36 59 60 59 36
250
1-story column
100 36
74 36
74 36
161 59 60 59 36
500
11-D19
（2.53%）
hoops
2-D6＠50
（0.51%）
36 74
36 89
2-story column
140
140
500
hoops
5-D6＠40
（0.80%）
20-D19
（2.30%）
36 74
36 59 60 5936
250
36 74
140
140
500
11-D19
（2.53%）
hoops
2-D6＠50
（0.51%）
36 74 70 70 70 70 74 36
74 36
Guideline [1]. The beam re-bars are anchored into beam-column joint with 90 degrees hook. The
anchorage length from the face of the beam joint is also satisfied with the AIJ Guideline [1]. The
anchorage length of the top first layer reinforcement (green reinforcement in Fig. 2.2 (c), (d)) from the
tail length is also satisfied with the AIJ Guideline [1]. The specimen O-ht is provided with haunch and
four reinforcements (blue reinforcement in Fig. 2.2 (d)) inclined 30 degrees at the corner of the joint.
The inclined reinforcements are anchored into column with a 180 degree hook and into beam on
straight anchorage.
161
59 60 59 36
1-story column
Inclined
reinforcement
5-D19
hook anchorage 23d
36 74 51 78 51 74 36
hoops
2-D6@40
（0.32％）
3650
36 50
12-D19
（1.91％）
hoops
2-D6@40
（0.32％）
anchorage 35d
8-D19
（1.27％）
36 74 51 78 51 74 36
400
250
250
89 36
1-story column
140
74 36
36
140
428
500
36 59 60 59 36
250
2-story column
36 74 70 70 70 70 74 36
500
161
500
9-D19
（2.07%）
hoops
2-D6＠50
（0.51%）
250
Elevation of joint
(b) I-ht specimen
36 74
140
36 74
2-story column
36 59 60 59
36 74 70 70 70 70 74 36
500
140
74 36
36
428
500
36 59 60 59 36
250
hoops
5-D6＠40
（0.80%）
20-D19
（2.30%）
beam
36
250
Elevation of joint
(a) I-1t specimen
36
11-D19
（2.53%）
hoops
2-D6＠50
（0.51%）
stirrups
[email protected]
（1.54％）
8-D19
（1.27％）
36 74 51 78 51 74 36
400
beam
5036
12-D19
（1.91％）
278
450
5036
36 74 51 78 51 74 36
278
450
stirrups
[email protected]
（1.54％）
150
260
hoops
5-D6＠40
（0.80%）
18-D19
（2.07%）
36 59 60 59
161
500
89 36
1-story column
Inclined
reinforcement
5-D19
hook anchorage 23d
36 74 51 78 51 74 36
400
beam
12-D19
（2.21%）
250
250
Elevation of joint
(c) O-1t specimen
* d : diameter of the reinforcement
570
5036
stirrups
4-D6@125
（0.38%）
10-D19
（1.82%）
hoops
5-D6@40
(0.80%)
anchorage 35d
10-D19
（1.82%）
36 74 51 78 51 74 36
400
beam
152
152
hoops
5-D6@40
(0.80%)
278
450
570
12-D19
（2.21%）
3650
36 50
stirrups
6-D6@125
（0.38%）
36 74 51 78 51 74 36
278
450
5036
36 74 51 78 51 74 36
150
260
250
Elevation of joint
(d) O-ht specimen
Figure 2.2. Test specimen details of I-1t, I-ht, O-1t, O-ht
250
2.3. Material
Normal Portland cement concrete is used. Mechanical properties of concrete are shown in Table 2.1.
Deformed bar (JIS G3112) is used for longitudinal bars in columns, hoops and stirrups in the specimen.
The mechanical properties of deformed bars are listed in Table 2.2.
Table 2.1. Mechanical properties of concrete
specimen
I-1t, O-1t
I-ht, O-ht
Compressive
Strength
(MPa)
25.5
28.9
Young's
modulus
(GPa)
24.8
31.0
Tensile
Strength
(MPa)
2.31
2.51
Yield
Point
(MPa)
373*
389
Tensile
Strength
(MPa)
553
561
Table 2.2. Mechanical properties of steel
Sectional
Area
(mm2)
D6
32
D19
287
* 0.2% offset strength
Reinforcing
Bars
Young's
modulus
(GPa)
185
190
3. TEST SETUP
The loading setup is shown in Figure 3.1. The specimens are restrained the deformation out-of-plane.
Statically cyclic lateral load was applied at the top of the column. The distance between the loading
point and the face of the first-story column is 700mm. Actuator was used to apply the horizontal load.
Axial load was applied at the center of the first-story column by hydraulic lifter with capacity of
-450kN to 2000kN. The drift angle is defined to be divided the deformation at the point of the lateral
load by the height from the face of the first-story column to the point of the lateral load.
Slider
Restraining
jig
+
Pin
connection
700mm
1750mm
500
1250
Reaction Wall
Axial Load
Hydraulic lifter
-
250
Lateral Load
Actuator
+
-
Strong Floor
Figure 3.1. Test setup
The horizontal loading cycles are shown in Figure 3.2. Before the cycles of 0.5% story drift, applied
axial load was 500kN in constant considering the sustained load of the building. After that, the axial
force is applied -450kN in pull cycle and 2000kN in push cycle considering the effects of overturning
moment under severe earthquake. Displacements, loads, strains and deformations around
beam-column joint are measured.
6
Story drift angle, %
4
opening direction loading
2
0
-2
-4
1
2
3
4
5
6
7
8
9
cycle numaber
closing direction loading
-6
Figure 3.2. Loading history
4. TEST RESULTS
Relation of story drift and story shear of each specimen is shown in Fig. 4.1. Relation of story drift and
story shear before the story drift angle 0.5% are enlarged and also shown in Fig. 4.1. The position of
the strain gauges and the yield points of re-bars are also shown in Fig. 4.1. The cracking pattern on the
beam-column joint of the each specimen at story drift of 4% is shown in Fig 4.2. The solid lines show
the crack of opening direction loading, the dashed lines show the crack of closing direction loading
and the bold lines show remarkable cracks. The gray part shows the detachment of concrete.
4.1. I-1t specimen
In opening direction loading, flexural crack A of the first-story column and crack B of beam occurred
during the story drift of 0.2%. Shear crack C of beam and crack D of the first-column occurred during
the story drift of 0.5%. Flexural crack A extended to 1.2mm in width and maximum story shear force
519kN was attained at the story drift of 2%. Cracking E extended to 3.0mm in width during the story
drift of 3%. Totally, the cracks progressed with arcs pattern around a corner of beam-column joint.
Failure mode of I-1t is considered to be flexural failure of the first-story column judging from the
strains of the first-story column and crack appearance.
In closing direction loading, flexural crack a of the first-story column occurred during the story drift of
0.2%. Flexural crack b and shear crack c of the beam occurred during the story drift of 0.5%. Concrete
crushing d occurred at the corner of the joint during the story drift of 1.5%. Flexural crack a extended
to 1.4mm in width and maximum story shear force 899kN was attained at the story drift of 2%. Failure
mode of I-1t is considered to be flexural failure of the first-story column at the face of beam.
4.2. I-ht specimen
In both opening and closing direction loading, the outline of crack process resembled I-1t. In opening
direction loading, flexural crack A extended to 3.0mm in width and maximum story shear force 686kN
was attained at the story drift of 4%. Failure mode of I-ht is considered to be flexural failure of the
first-story column.
In closing direction loading, Flexural crack a extended to 1.4mm in width and maximum story shear
force 1049kN was attained at the story drift of 2.5%. Shear crack b extended to 4.0mm in width
during the story drift of 4%. Failure mode of I-ht is considered to be flexural failure of the first-story
column.
4.3. O-1t specimen
In opening direction loading, flexural crack A of the beam and crack B of the first-story column
occurred during the story drift of 0.2%. Shear crack of beam and diagonal crack C in beam-column
joint occurred during the story drift of 0.5%. Concrete crushing of the second-story column base
occurred during the story drift of 3%. Flexural crack B extended to 2.2mm in width and maximum
story shear force 525kN was attained at the story drift of 4%. Totally, the cracks progressed with arcs
pattern around a corner of beam-column joint. Failure mode of O-1t is considered to be flexural failure
of the first-story column.
In closing direction loading, diagonal crack a in beam-column joint, flexural crack b of the first-story
column and crack c of the beam occurred during the story drift of 0.2%. Shear crack of the first-story
column and the beam occurred during the story drift of 0.5%. Concrete crushing at the corner of the
joint occurred during the story drift of 1.5%. Flexural crack a extended to 0.15mm in width and
maximum story shear force 826kN was attained at the story drift of 2.5%. Failure mode of O-1t is
considered to be flexural failure of joint failure.
4.4. O-ht specimen
In both opening and closing direction loading, the outline of crack process resembled O-1t. In opening
direction loading, flexural crack A at the haunch occurred during the story drift of 0.2%. Flexural
crack B extended to 4.0mm in width and maximum story shear force 686kN was attained at the story
drift of 4%. Failure mode of O-ht is considered to be flexural failure of the first-story column.
In closing direction loading, Concrete crushing d of the haunch occurred and diagonal crack a
extended to 1.4mm in width and maximum story shear force 990kN was attained at the story drift of
2%. After that, Concrete crushing d of the haunch progressed and diagonal crack from around
extended joint increased and extended. Failure mode of O-ht is considered to be flexural failure of
joint failure.
-4%
C1
B4
B3
500
Load (kN)
H4
B8
W1
W2
C7 C5
S1
W3
-30
-5%
1000
-4%
S1
C1
W2 W1
W3 B4
+566kN
2%
3%
4%
Qmax= +519kN
+519kN
5%
1000
C5
C7 C4
H1 H3
-5%
B3
A2
500
H4
C4
S1
B8
-3%
-2%
C3
H1
C5
(a) I-1t specimen
1%
-1%
2%
Qmax
Yield bar
4%
5%
1000
Qmax= +525kN
C1
B4 H1
+539kN
3%
c
+481kN
Qu
500
Q’u
-5%
C1
B9
H3
400
200
-500
-1000
-0.5%
-864kN
C5, S1
C3
C2, H3 Qmax= -826kN
-926kN
C8
B9
Q’u
Q
c u
c
-0.2%
0.2% 0.5%
Load (kN)
Load (kN)
C8
-4%
-30
-20
2%
+610kN
5%
C5 H4
H1W3
Qmax
Yield bar
c
Qu
0.2% 0.5%
600 -0.5% -0.2%
400
200
0
-200
C6
C13 Q’
c u
-400
Qmax= -1049kN
-600
Q
c u
Before R=±1/200
C8,C12
-800
C11(Compressive)
-4 -3 -2 -1 0 1 2 3 4
-20
-10
0
10
20
30
40
Deformation (mm)
(b) I-ht specimen
-3%
H1
H2
H3
1%
-1%
-2%
2%
3%
B5
C1 Qmax= +651kN H1
C11
A2
+674kN
+571kN
A1
Qmax
Yield bar
4%
5%
H2
c
B9
c
400 -0.5%
-0.2%
Qu
Q’u
0.2% 0.5%
200
-500
0
-200
-200
-1000kN
-1201kN
Before R=±1/200
-600
-4 -3 -2 -1 0 1 2 3 4 -1500
-10
0
10
20
30
40
-40
-30
Deformation (mm)
(c) O-1t specimen
4%
Q’
c u
0
-1000
3%
Qmax= +686kN
C7
C8 B9
0
1%
W2
C11 A2
W1 A5
A1
A4
+665kN
H1 C6
C5 H2
B9
H3 C8
C5
-400
-1500
-40
H4
-1%
C11 C12
C13
A2
A1 B5
c
0
-4%
-3%
-2%
C11 C12 C13
A1
B5
B4
0 W1 W2 W3
0.2% 0.5%
600 -0.5% -0.2%
400
200
-500
C3
0
C6
-200
-1000 -1027kN
-400
S1b Qmax= -899kN
-600
C1(Compressive)
-1220kN
C2
Before R=±1/200
C8
-800
-4 -3 -2 -1 0 1 2 3 4 -1500
-20
-10
0
10
20
30
40
-40
-30
Deformation (mm)
C1 C2
B4
500
1%
C7
W3
-886kN
-953kN
-1500
-40
-1%
Qmax
Yield bar
C3
H1 C6
C5 H2
B9
H3 C8
-500
-1000
-2%
C2
B5
C4
S1
0
-3%
Load (kN)
-5%
1000
Qmax= -990kN
-20
C8
C5
C12 C13
H3 B9
Q’u
c
Qu
-400
Before R=±1/200
-600
-4 -3 -2 -1 0 1 2 3 4
-10
0
10
20
30
40
Deformation (mm)
c
(d) O-ht specimen
Figure 4.1. Relation of story drift and story shear
D
A
B A
d
b
b
a
a
A
B
d
b
A
c
C
B
b
C
E
C
c
(a) I-1t specimen
(b) I-ht specimen
a
(c) O-1t specimen
a
c
(d) O-ht specimen
Figure 4.2. Observed crack pattern
5. EQUATION OF ULTIMATE STRENGTH
In opening direction loading, failure mode of all specimens is considered to be flexural failure of the
first-story column at the face of beam judging from the strains in the beam-column joint and crack
appearance. In closing direction loading, failure mode of I-1t, I-ht is also considered to be flexural
failure of the first-story column at the face of beam. Failure mode of O-1t, O-ht is considered to be
joint failure but the reinforcement of the first-story column is yielded. Each flexural strengths of the
first-story column cQu, which is divided ultimate flexural moment Mu calculated based on Navier
hypothesis by the height from critical section (I-1t, O-1t : at the face of the first-story column (A) in
Fig 2.1, I-ht, O-ht : at the face of haunch (B) in Fig 2.1) to the point of the lateral load, is shown in Fig
4.1. However, the test results do not match with each flexural strength. To judge from the prominent
flexural crack, the critical section is considered to move into the joint. Therefore the critical section is
reset according to 5.1.
5.1. Critical section of the first-story column in opening direction loading
In opening direction loading, the compressive strut of the specimens is assumed as shown in Fig 5.1. It
is considered that the first-story column is yielded because shear force of first-story column is pulled
by tensile force of reinforcement arranged at the bottom in the beam. Therefore the critical section of
the flexural failure of the first-story column is set to be at the center of gravity position of bottom
reinforcement.
The specimen O-1t, O-ht is observed to be prominent crack C in Fig 4.2 (c), (d). The effective depth is
smaller than normal depth due to that prominent crack. Therefore the effective depth is recalculated
based on the assumption shown below. The equilibrium condition for effective section shown in Fig.
5.1 (c) is given by Eq. (1). The compression Cout of the concrete section resisted by equilibrium for
Cout and tensile of the joint hoops Σawσwy shown in the blue tie width ΔD in Fig 5.1 (b) is given by Eq.
(2). The effective depth Deff is given by Eq. (3).
Cout
d

 awwy Dc1  Dc 2
(1)
Cout   D  bc  Fc
(2)
Deff  lb   D  lb 
a 
w
bb Fc
wy

d
 Dc1
Dc1  Dc 2
(3)
where, d : effective depth of beam, Dc1 : depth of first-story column, Dc2 : depth of second-story
column, bc : width of first-story column, Fc : compressive strength of concrete, aw : cross sectional area
of joint hoops, σwy : tensile yield point of joint hoops, lb : the length from the face of the beam to the
starting point of the 90 degrees hooked shown in Fig 5.1.
Deff
Dc1
lb
←
T
the center of
the gravity line
critical
line
←
←
T
∆D
Cout
a
Σawσwy
d
d
Dc1Dc2
Dc2
(a) I-1t, I-ht specimen
Cout
Σawσwy
Dc1-Dc2
(b) O-1t, O-ht specimen
(c) equilibrium for Cout and
tensile of the joint hoops Σawσwy
Figure 5.1. Critical section of the first-story column in opening direction
5.2. Critical section of the first-story column in closing direction loading
In closing direction loading, flexural failure of first-story column is considered as shown in Fig 5.2. It
is considered that the first-story column is yielded because shear force of first-story column is resisted
by compression range xn of the beam. The equilibrium condition for that compression range xn is given
by Eq. (4). The average stress of concrete is assumed as 85% of the compressive strength of the
concrete.
xn =
Qu
0.85  bb  Fc
c
(4)
where, bb : depth of beam, Fc : compressive strength of the concrete
Therefore, the critical section of the flexural failure of the first-story column is set to be at the center
of compression range of beam xn/2. However the critical section of the flexural failure of the first-story
column of the specimen I-ht, O-ht with haunch is reset to be the section based on the assumption
shown below.
The failure plane of the concrete by unconfined compression is considered to be plane inclined around
1:2 (Carpinteri A. et al., 2001) shown Fig 5.2 (b). The concrete block shown in Fig 5.2 (a) is also
assumed to be failure plane of the concrete inclined 1:2 with the length 5 xn. Besides, the specimens
with haunch shown in Fig 5.2 (c), (d) are also assumed to be failure plane of the concrete inclined 1:2
with the length 5 xn. The compression range xnh of the specimens with haunch is given by Eq. (5).
Therefore the critical section of the flexural failure of the first-story column is reset to be at the center
of compression range of beam xnh/2.
xnh  xn (1  2 tan )
(5)
Fc
Fc
2
Fch
11
closing
closing
(b) failure surface in
unconfined compression
Fch
2 xn
θ
θ 2 xnn
(a) specimen without haunch
xn
5 xn
2 xntanθ
xn
5 xn
xnh
2 xn
xnh
(c) failure surface of haunch
(d) specimen with haunch
Figure 5.2. Critical section of the first-story column in closing direction loading
5.3. Modelling of the joint failure in closing direction loading (O-1t, O-ht)
In closing direction loading, the prominent crack a of the specimen O-1t, O-ht shown in Fig 4.2 (c),
(d) progress at about 45 degrees. The failure mode of specimens O-1t and O-ht is considered to be
joint failure mode shown in Fig 5.3 (a). The point at intersection of failure line of 45 degrees from
outside of second-story column and the compression range x2c of the second-story column is reflected
to the beam. The compression range x2c and ultimate flexural moment of the second-story column 2cMu
is calculated by the way based on Navier hypothesis. The range from that point to extreme
compression fiber is assumed to be the compression range xnb of the beam.
The joint failure strength jQu is considered by the equilibrium shown in Fig 5.3 (b). All the tensile and
compression reinforcement of the beam are assumed to be yielded. Tensile force and compression
force represent Ts and Cs. The compression Cc of the concrete of the beam is given by Eq. (6). The
beam moment is calculated at the center of the beam. The compression Cc is assumed to be acted at
xnb/2. The moment bMu of the beam is given by Eq. (7). The joint failure strength jQu is calculated by
Eq. (8). The moment jMu of the ultimate joint strength is calculated as a total of the moment 2cMu and
bMu. The length L is from the center of the depth of the beam to the lateral load.
Cc  j Qu  Ts  Cs
(6)
b
M u  Ts  gts  Cs  g cs  Cc 
j
Q 'u 
j
Mu
L

2c
Db  xnb
2
(7)
M u  b M 'u
L
(8)
However, The joint failure strength jQu of the specimen O-ht with haunch is considered by the
equilibrium shown in Fig 5.3 (c). Compression reinforcements of the beam are assumed to be not
yielded. Instead, inclined reinforcements are assumed to be yielded. The moment jMu of the ultimate
joint strength is calculated in the same way. The depth of the beam is included in the part of haunch.
←
Q'
xn2c
45°
(a) O-1t, O-ht specimen
Cs
Cc
↓
gcs
gts
L
xnb /2
Ts
2c
←
Mu
(b) O-1t specimen
Db
L
gcs
C
Cc s
↓
xnb /2
j
←
xnb
←
Q'
u
←
j
gts
Ts
2c
←
Mu
(c) O-ht specimen
Figure 5.3. Modelling of the joint failure in closing direction loading (O-1t, O-ht)
Db
u
5.4. Comparison the calculated and observed story shear
Comparison the calculated and observed story shear is shown in Fig 5.4. The dashed lines show ±10%
error lines. Approximately, in both opening and closing direction loading, the strength of the observed
failure mode is evaluated as shown in Fig 5.4. On the other hand, in closing direction loading, the
observed failure mode of the specimens O-1t, O-ht is considered to be joint failure. However,
Modified flexural strengths of the first-story column cQ’u are lower than joint failure strengths jQu and
the observed failure mode does not correspond to the calculated failure mode.
1200
(kN)
1.1
Q'u modified flexural failure of the first-story
column in opening direction loading
c
I-ht
1000
story shear (test)
0.9
Q'u modified flexural failure of the first-story
column in closing direction loading
c
O-ht
Q'u joint failure in closing direction loading
I-1t
O-1t
800
600
j
I-ht
O-ht
O-1t
I-1t
400
400
600
800
1000
story shear (calculation)
(kN)
1200
Figure 5.4. Comparison the calculated and observed story shear
6. CONCLUSIONS
The followings are concluded:
1） In the opening direction loading, all the specimens showed flexural failure of first-story column.
2） In the closing direction loading, the specimens in which the first-story column are extended
toward inside show flexural failure of first-story column, whereas the specimens in which the
first-story column are extended toward outside showed joint failure.
3） Haunch at the corner of the joint is effective on improving strength and stiffness.
4） The proposed equations of the flexural strength of the first-story column and the joint failure can
estimate the strength obtained by experiments.
ACKNOWLEDGEMENT
The authors acknowledge the supports by the Grant-in-aid for researches on the building codes improvement by
Ministry of Land, Infrastructure, Transport and Tourism, Japan.
REFERENCES
Architectural Institute of Japan (AIJ). All Standard for Structural Calculation of Reinforced Concrete Structure.
Tokyo, Japan, 2010. (in Japanese)
Kotani, G., et al. (2011). Experimental Study on Joint Failure Mode of Soft-First-Story RC Buildings Part 1~3.
Architectural Institute of Japan Tokai Chapter Architectural Research Meeting 49:2, 253-264.
Kato, Y., et al. (2012). Experimental Study on Joint Failure Mode of Soft-First-Story RC Buildings Part 4~5.
Architectural Institute of Japan Tokai Chapter Architectural Research Meeting 50:2, 173-176, 189-192.
Carpinteri, A. et al, (2001) Size-scale and slenderness influence on the compressive strain-softening behavior of
concrete, Fatigue and Fracture of Engineering Materials and Structures, Vol. 24, 441-450.