Proceedings of the International Symposium on Engineering Lessons Learned fromthe 2011 Great East Japan Earthquake, March 1-4, 2012, Tokyo, JapanSEISMIC DAMAGE OF A NINE-STORYRC RESIDENTIAL BUILDING IN SENDAIDESIGNED BY OLD SEISMIC CODES
Hitoshi SHIOHARA1, Tomoaki AKIYAMA2,
Kazuhiko WATANABE3 and Keisuke OKIHARA4
1 Associate Professor, Department of Architectural Engineering, the University of Tokyo, Tokyo,

Japan, shiohara@arch.t.u-tokyo.ac.jp
2 Senior Engineer, Tokyo Soil Research Co., LTD., Tokyo, Japan akiyama-t@tokyosoil.co.jp
3 Senior Engineer, Urban Renaissance Agency, Tokyo, Japan

k-watanabe07@ur-net.go.jp
4 Graduate Student, Department of Architectural Engineering, the University of Tokyo

Tokyo, Japan, okihara@rcs.arch.t.u-tokyo.ac.jp

ABSTRACT: Structural damage is reported for a nine-story reinforced concrete
residential building which experienced the 2011 Tohoku-chiho Taiheiyo-oki Earthquake
in Sendai. The structural system is moment resisting frames in longitudinal direction andcoupled shear wall system in the transverse direction. The failure mode of beam-column
joints are compared to the prediction by the current seismic design guidelines. The
validity of their provisions on joint shear strength and the other specifications are
discussed.
Key Words: reinforced concrete, residential building, seismic retrofit, beam-column
joint, shear strength, structural damage, seismic codes, seismic design

INTRODUCTION
Investigation on damage of buildings following strong earthquakes provides an invaluable opportunity
for structural engineers to validate the current seismic codes as well as performance based design
methodology having been developed for the control of seismic damage. Types of failure of members,
such as flexural or shear are concerns of structural engineers who decide the detailing of structuralmembers. So keeping records of damage and structural detailing of members are of great importance.
In this report, a case of a nine-story reinforced concrete (RC) residential building in Sendai (Nbuilding) are described. The building was constructed in 1969 and suffered extensive damage by the2011 Tohoku-chiho Taiheiyo-oki Earthquake on March 11 and its aftershocks. The overviewing photoof the building is shown in Fig. 1.
Although this building escaped from a structural collapse, the all the leaseholder in the offices at
the first and the second floor and the apartments at the other floors had evacuated. Damage occurs to
structural members including columns, beams, shear walls and beam-column joints. They suffered1145

extensive damage particularly at the first story. Extensive shear cracks, concrete crush and buckling of
longitudinal reinforcements were observed in many columns and shear walls. Many visible diagonal
cracks were found from outside on the exterior beam-column joints at the fourth floor through 9th
floor. Major shear cracks on coupling beams were also found in transverse direction and non-structural
reinforced concrete walls in longitudinal direction.
The extent and distribution of damage are reported and some preliminary result of correlation
with seismic vulnerability assessment done in 2011 are discussed. The failure mode of beam-column
joints are compared to the prediction by the current seismic design guidelines. The validity of therecent provisions for joint shear strength are discussed.

DAMAGED BUILDING
The location of the N-building is in Taihaku ward, Sendai City. It is the neighborhood of JR
Nagamachi Station which is about 5 km south of JR Sendai Station. Seismic intensity in JMA scale
was 5+ (five major) and 5- (five minor) for the main shock on Mach 11 and the largest aftershock on
April 7 respectively. No death or injury is reported due to this building. Taihaku ward is comercial
and residential area and densely populated. The death toll in Taihaku ward is 8, while the population is218,704 (as of April 1, 2010). So the percentage of death is very small. There was no tsunami
inundation in Taihaku ward.
The building site is flat and on an alluvial plain. Design and construction was completed in 1969.
It experienced 1978 Miyagi-ken oki Earthquake as well as recent major earthquakes in 2003 and 2005.
It is reported that it had slight damage due to the past earthquakes but has been functional. So thebuilding has been continuously used. No repair work nor major seismic retrofit has been done to thisbuilding before March 11, 2011.
The elevations and the plans are shown in Figs. 2 through 6. The building is a nine story
reinforced concrete building. The use of the first and second floor is municipal office and medical
office, while the third floor through ninth floor are apartment units for rent. A corridor are placed oneach floor above 3rd floor at the mid bay of the transverse direction which accommodates for theaccess to each apartment unit.
The story height is 3.6m, 3.3m and 2.75-2.6m for the 1st, the 2nd and the the upper floor
respectively. It has a one story in the basement and a three-storied penthouse. The heigh of the roof
floor level is 26.15 meter from the ground level. The building has a foundation supported byreinforced concrete piles of 5 meter length. The type of supporting soil is of category II designated by
the building standard law enforcement orders.
The structural system consists of four regular moment resisting frames in longitudinal direction
with seven bays with span length of 5.4 m. The transverse direction are coupled shear walls at thirdstory and above with wall length of 8 m and coupled beam length of 2m. The structural plan andelevation is regular at the third story and above, whereas the floor of the first and second story areextended one span to outside at three sides and provide open space for the municipal or medical
offices. There are some reinforced concrete shear walls and non-structural concrete block masonrywalls at these two stories but the direction and the placement of the walls are not in consistent to theplacement of the coupled shear walls above the 3rd story.
The types of structural members are reinforced concrete (RC) but steel reinforced concrete (SRC).
SRC is also used. SRC is a type of member with composite section of structural steel lattice encased inreinforced concrete. The beams and columns of the first story (above the 1st floor level) through thethird story are SRC members. The basement and the fourth story and above as well as the penthouseare of RC constrution. The girder for the exterior frame in longitudinal direction is of wall girder type,i.e. with narrow and deep section for the third story and above.
The concrete is normal weight with design compressive strength of 18MPa or 21MPa. The
longitudinal reinforcement is of Grade SD35 with specified yield point of 345MPa. The concrete core1146

sample tests for compressive strength were carried out in 1999, the concrete retained the design
strength and were in sound condition reportedly.

SEISMIC EVALUATIONA seismic vulnerability assessment of the building was carried out in 1999. Then reassessment
was done in 2011 to consider the influence of 2003 Sanriku-minami Earthquake and 2005 Miyagi-ken
Nambu Earthquake preparing for seismic retrofit work. The assessments were based on the Seismic
Evaluation Standards1) of the Japan Building Disaster Prevention Association (BDPA).
The method of the Japanese Seismic Evaluation Standards are briefly explained here. It provides apredefined procedures to calculate the value of seismic index (Is), which is a value given for each storyof a building. The Is value for the first story is a sort of base shear coefficient at collapse mechanism;
calculated as the sum of the lateral capacity of the lateral resisting elements such as columns and shear
walls which support the weight above the story. But the lateral capacity of each element are factored
by a prescribed modifier considering the ductility. The factor ranges from approximately 0.8 to 3.0
given as tabulated values or calculated based on its a) dimension, b) type of member, c) shape factor
such as shear-to-span ratio, d) failure type and e) the ratio of shear capacity to shear strength demand.
So, the Is value is intended to define such that seismic vulnerability could be represented in terms of
maximum base shear coefficient of a linearly elastic system subjected to a base motion to which thestory of the building remains within life safety limit. The Is values of 0.6 or less is a recommended
criteria of seismic retrofit otherwise special performance objectives are preferred. There are three
options of modeling preciseness for the analyses. Level I is the simplest and the lateral capacity isroughly estimated based on the type and horizontal sectional area of lateral resisting members. Level
III is the most sophisticated considering full failure mechanism of a structural system, whereas Level
II is a compromised version of Level III by neglecting the beam sway mechanism.
The seismic index Is for the N-building calculated in 2011 are listed in Table 1. They adopted themodeling of level II for the analysis. The results of the assessment of the N-building are summarized
as follows. For the longitudinal direction (X-direction), the Is value for 2nd through 9th stories are lessthan 0.60 while the Is value for the first story is larger than 0.60. One of the reasons of the lower Is
value for the upper floors is that the most of the columns in Y1 and Y4 frames are short column withshear-to-span ratio of 1.6 and categorized as non-ductile to which modification factors of 0.8 isapplied. The columns in Y2 and Y3 frames are identified as shear failure column because they havereinforced concrete monolithic wing walls and categorized as non-ductile due to small shear-to-span
ratio. The Is value for the first and the second story is relatively larger. Most of the columns are ofshear failure type. But RC shear wall are placed randomly and provide large lateral capacity. The
shear wall in the second floor provide eccentric lateral stiffness and penalty factor SD is applied; i.e. apenalty factor considering the irregularities of stiffness eccentricity. Thus the Is value for the 2nd story
is lower than that of the first story.
For the transverse direction (Y-direction), the Is value for the first, second and fourth story are lessthan 0.60 whereas the other stories have the Is value larger than 0.6. Most of the columns are of shear
failure type and eccentric placement of shear wall are attributed to the lower Is value for the first andthe second story. Combination of high shear force and high tensile axial force are expected to thecolumns locating beneath the boundary column of the rocking shear walls in the transverse direction
from 3rd to 9th story. In addition to that, the SRC column of the first story have deficiency that thebottom of the steel shape is not continuous into the foundation but just ends at the first floor level. As
the bottom section of the column has only longitudinal reinforcement, damage concentrates to thislocally weak section when it is subjected to bending and high axial tension.
It is summarized by the discussion above that the most probable scenario of seismic damage
derived from the seismic vulnerability assessment were; (1) the shear failure of column above the 3rdstory in the longitudinal moment frames and (2) local damage of SRC column at the first story in the1147

transverse direction.

OBSERVED DAMAGE TO STRUCTURAL COMPONENTS
The damage of members were photographed and each member was graded into five levels. The
grading was based on the maximum crack width, the extent of concrete crushing as well as buckling of
longitudinal steel. The criteria for the grading are explained in Table 2.
The evaluated grade of the columns and walls are shown in Figs. 2 through 6. The first story
column at X1-Y1 suffered the damage of the severest grade of V. The Fig. 7 shows the photo of thecolumn. Cover concrete spalled off at the bottom of the column and the longitudinal bars are buckled.
Flexural yielding at the base occurred and high axial force variation due to rocking wall at the above
level cause the severe damage. Possibility of this problem had been already pointed out by thevulnerability assessment done in 2011. Story drift at the first story seems to be the largest because thenumber of columns with grade III or severer were observed only for the first story. This interpretation
may be endorsed by the fact that most of the grass fracture were observed only at the first story. The
damage of columns at the second story is not significant.
The other severe damage was observed on the boundary beams which consist of coupled shear
walls in transverse direction starting from the 4th floor level through the roof floor level. Damage
grade of the beams were III from the fourth floor through seventh floor as shown in the elevation of X1
Frame in Fig. 6. The section of the beams is 350mm wide and 600mm deep where the longitudinal
reinforcements are 5-D22 bars for top and 3-D22 bars for bottom. The stirrups are 9mm diameter plain
bar with spacing of 200mm. No shear failure was not observed but the stirrups were not sufficient forcontrol the residual crack width less than 1.0mm.
Some of the exterior RC/SRC columns in Y4 frames suffered a shear failure at the third, fourthand fifth story with damage grade of IV. Fig. 9 shows the shear cracks on the columns.
By the image on the photo of the exterior side of Y4 frames shown in Fig. 10, it is revealed thatsome beam-column joints have significantly cracked and concrete crushing was also found. The
cracks originated from the corner of the window opening and proceeded into the center of joint.
Crushing of concrete as well as tile peeled off at the crossing point of diagonal cracks were evident. It
is presumed that longitudinal direction was imposed very large story drift, because the non-structural
RC partitions along the corridors in the longitudinal direction between Y2 frame and Y3 frame had
been significantly failed in shear.
CORRELATION OF DAMAGE AND SEISMIC VULNERABILITY ASSESSMENT
The N-building has no tilting remained and overall damage level of the building is moderate. But thebuilding had been entirely evacuated in June 2011 when the author visited this building site. There isno plan of repairing at the time of this paper submission. Considering the seismic intensity of 5+, thedamage level of this building is relatively higher than the similar buildings around this site in this area.
So this building should be more vulnerable than the other similar buildings.
The distribution of damage in vertical direction is not in good correlation to the Is distribution.
The Is value of the third story through 8th story in the longitudinal direction is minimum in thisbuilding and Is value is relatively larger for the first story. But damage is severer particularly to thefirst story. This is partly due to the poor detailing of the base of first story column of SRC.
The coupled shear wall system in transverse direction seems to perform well except poor control
cracking performance of coupling beams. Although the shear failure of column above the 3rd story in
the longitudinal moment were predicted, the reality is the shear failed column are observed at the thirdand fourth story only. This may be attributed to the neglect of the lateral resisting contribution of
auxiliary components of RC non-structural wall components abundant in longitudinal direction.

1148

FAILURE MODE OF BEAM-COLUMN JOINT SUB-STRUCTURE
The seismic evaluation standard1) have no predefined equations to consider beam-column joints withpoor performance. But as shown in Fig. 5, diagonal cracks were observed at many beam-column
joints in the longitudinal frame of Y4. So, the failure type is evaluated by the current seismic design.
The sections of beam-column joints are shown in Fig. 8 for the beam-column joint at fifth floor
level and seventh floor level taken from the structural drawing. They are crucial beam-column joints
provided with joint hoops with common spacing to the hoops in the column according to the structural
drawing. The flexural strength, shear strength and joint shear strength are calculated based on thedesign strength of material and design equations as follows,
Flexural ultimate moment M u of a beam and column section are calculated by a equation (1) and(2) respectively,
M u = 0.9at fy d

(1)

"
N %
M u = 0.8at fy D + 0.5ND $ 1!
# bDFc '&(2)

where, at : sum of the sectional area of tensile rebar in the beam, fy : specified yield point of thetensile rebar, and d : effective depth of the beam, D : full depth of the column, N : axial force incompression, and Fc : concrete compressive strength. The axial force of the column is calculated
considering the dead load of tributary area for gravity load.
The shear strength of the beams and columns are calculated using the equations for shear adopted
in the AIJ Guidelines for RC Buildings2) .
The joint shear demand Vj is calculated by,
V j = at fy + at! fy " Vc

(3)

where, at : sum of the sectional area of tensile rebar for positive moment in the beam, at! : sum of thesectional area of tensile rebar for negative moment in the beam, fy : yield point of the tensile rebar, and
Vc : column shear at the ultimate flexural strength of beam at the column face.
The joint shear capacity Vju in N is calculated by the equation2),
V ju = 0.8!" Fc0.7b j D(4)

where, ! : shape factor ( =1.0 for crucial beam-column joints), ! : modification factor of transverse
beam (= 0.85 for joint covered with beams at three sides), Fc : concrete compressive strength in MPa,b j : effective width of the joint in mm and D : full depth of the column in mm.
Table 3 lists the story shear capacities in kN for the RC beam-column joints at X5-Y4 (common to
X5-Y4 ) , corresponding to a) shear failure of column b) shear failure of beam, c) shear failure of beamcolumn joint, d) column yielding mechanism, and e) beam yielding mechanism. The flexural capacityof the beams are always the smallest of the capacities. This means the analysis by modeling Level II
is inappropriate to this building. The ratios of joint shear demand to joint shear capacity if more than
2.0. Thus these beam-column joint is lightly reinforced joint and has been considered to be safe tojoint shear failure. But in reality, the joint shear failure were observed. It is obviously inconsistent
with the joint shear design currently adopted to the seismic design codes for RC structures.
Three dimensional shaking table tests of four story full scale RC building at E-Defense has

1149

confirms the importance of beam-to-column strength ratio recently3). RC beam-column joints with thecolumn-to-beam strength ratio closed 1.0 showed severe joint shear failure than beam yielding. The
series of tests of the author on beam-column joints by authors also revealed the joint with beam-tocolumn strength ratio of 1.0 to 2.0 showed joint failure. The author are developing the theoreticalmodel to explain the failure of beam-column joint with the strength ratio of 1.0.4) The calculated valueof column-to-beam strength ratio listed in Table 3 shows that the ratio is in the range of 1.26 to 1.48 if
the column capacity is calculated using the axial force for column tributary area excluding thetributary area of the wall. It is confirmed that the column-to-beam strength ratio of the beam-column
joint showing severe diagonal cracking ranges between 1.0 and 1.5 which is vulnerable to joint shear
failure predicted by recent research results.

CONCLUDING REMARKS
The extent and distribution of damage are reported for a nine-story reinforced concrete residentialbuilding in Sendai (N-building) designed and constructed in 1969 by old design codes. It is revealed
from the investigation that the N-building escaped from a collapse and no tilting remained.
The building had life safety performance and overall damage level of the building was moderate.
Considering the seismic intensity of 5+, the damage level of structural members of this building isrelatively higher than the similar buildings around this site in this area.
The first story SRC column subjected to bending and high axial tension by the rocking wall above
showed the severest damaged in this building. It is due to the deficiency of steel lattice that is notcontinuous nor embedded into the foundation but just ends at the first floor level which allowed
concentration of local deformation adjacent to the weak section at the bottom of the column.
The failure of beam-column joints were observed to the joints which conforms to the current
seismic design codes. The calculated margin of joint shear strength is 2.0 or more for the beamcolumn joint, whereas the value of column-to-beam strength ratio is in the range of 1.26 to 1.48. It is
confirmed that the column-to-beam strength ratio between 1.0 and 1.5 is vulnerable to joint shear
failure.
REFERENCES
1.
2.
3.

4.
5.

Japan Building Disaster Prevention Association, Seismic Evaluation Standard - Revision of 2009,2009. (in Japanese)
Architectural Institute of Japan, Design Guidelines for Earthquake Resistant Reinforced Concrete
Buildings Based on Inelastic Displacement Concept, 1999. (in Japanese)
T. Nagae, K. Tahara, K. Fukuyama, T. Matsumori, H. Shiohara, T. Kabeyasawa, S. Kono, M.
Nishiyara and I. Nishiyama, Large-Scale Shaking Table Tests on a Four-Story Building, Journalof Structural and Construction Engineering, Architectural Institute of Japan, Vol. 76, No. 669,
Nov. 2011, pp. 1961-1970. (in Japanese)
H. Shiohara and F. Kusuhara, An Overlooked Failure Mechanism of Reinforced Concrete Beamcolumn Joints. Proc. 9th NCEE, July 25-29, 2010, Toronto, Canada, Paper No. 822.
Hitoshi Shiohara, Reinforced Concrete Beam-column Joints : An Overlooked Failure Mechanism.
ACI Structural Journal, Vol. 109, No. 1, January-February, 2012, pp. 65-74.

1150

Table 1 Values of Seismic Index Is
Story

Longitudinal
direction

Transvers
direction

9
8
7
6
5
4
3
2
1

0.37
0.27
0.23
0.20
0.21
0.19
0.20
0.44
0.62

1.49
1.04
0.82
0.70
0.62
0.51
0.71
0.44
0.39

Table 2 Damage grading criteria of RC components

0I

Daamage grade

Criteria

No damageSlightNo damage
Structural concrete cracking of width less than 0.2mm
Structural concrete cracking of width larger than 0.2mm
and less than 1.0mm.
Structural concrete cracking of width larger than 1.0mm
and less than 2.0mm.
Structural concrete cracking of width larger than 2.0mm,
with cover concrete spalling and visible reinforcement
Cover concrete spalling off, with some concrete crushes andlongitudinal reinforcement buckling

II Minor
III Moderate
IV Major
V Severe1151

Table 3 Calculated story shear at mechanism of beam-column joints, column-to-beam strength ratio
and joint shear strength margin
Shhear failurre
Fleexural hinggeColumn--to-beam
Joint
in kN
in kN
strengtth ratio
shear
strengthcolumn column
column
beam
joint
beam
case 1case 2 margin*case 1* case 2*
9FL
544.4
858.7
863.4
522.5
396.7
231.7
2.25
1.71
3.73
8FL
555.0
929.1
984.0
650.8
454.0
320.2
2.03
1.42
3.07
7FL
589.2 1043.2 1112.3
751.5
496.7
335.0
2.24
1.48
3.32
6FL
799.7 1148.5 1150.1
906.6
574.8
432.2
2.10
1.33
2.66
5FL
907.8 1162.5 1624.0 1082.9
664.0
528.3
2.05
1.26
3.07
* case 1: axial force of column is considering tributary area for both column and wall as shown in the figure
below, case 2: axial force of column is considering tributary area for column only, Joint shear strength
margin = joint shear demand Vj /joint shear capacity Vju

Wall
Columnfloor plan
Tributary area of gravity load

Fig. 1 Overview of the N-Building from the west side

1152

Y5

III

Y4

IIs O

II

II

O

IVs

IIIs

IIs

IIIs

Is

O

IIs

II

IIs

II

III

O

I

I

Is

II IVs

O

O

Is

Is

IIs

O

O

Is

Is

III

O

V

II

V

IIs

Y3

O

O

Is
Is

Entrance
Vs

Y2

III

O

I

O

IIIs

IIIs

IIs

X5

X6

X7

O

IV

see Fig. 7
Y1

IV

Y0

III

I

V

V

X0

X1

IIIs

X2

III

X3

IIIs

X4

X8

Fig. 2 Plan of 1st floor and damage grade of structural members
Is

Y5
Y4

Y3

I

I

II

Is

O

IIs

Is

I

I

O

O

O

O

I

O

I

O

O

Vs
O

O

O

Is

O

O

Is

Is

Is

Is

O

O

III

O

Is

II

II

Is

I

I

I

Y2

O

IIs

Is

Y1

III

IIIs

I
O

I

I

I
I

Is

Y0

IIs

III

O

O

O

I

I

I

O

X0

X1

X2

X3

X4

X5

X6

X7

X8

Fig. 3 Plan of 2nd floor and damage grade of structural members

Y4

IVs

IVs

Y3
Is

Is

Is

Is

Is

Is

Is

Y2
IIIs

Y1

X1

X2

IVs

IVs

IIs

IIs

X3

X4

X5

X6

X7

X8

Fig. 4 Plan of 3rd floor and damage grade of structural members

1153

PHRFL 36,150

shear crack on beam-column joint
RFL

26,1509FL

23,3508FL

20,7507FL

18,1506FL

15,5505FL

12,8504FL

10,150

3FL

7,400

2FL

4,100

1FL

500

see Fig. 10

IVs
IVs

IVs

IVs

IVs

IVs

O

O

I

O

I

O

Is

Is

II

O IIs

O

Is

Is

I

I

O IIs

II IIIII

5 400

8 = 43 200

GL

X8

X7

X6

X5

X4

X3

X2

X1

X0

Unit in mm

Fig. 5 Elevation of Y4 Frame and damage grade of structural members

steel shapein concrete

III
III
III
IIs
Is
see Fig. 7

O

IIIs

I

Is

Is

O

V III

V IV

O

O

III

II

4 500

6 000

Y0

Y1

6 000

Y2

6 000

Y3

4 500

Y4

unit in mm
Y5

Fig. 6 Elevation of X1 Frame and damage grade of structural members

1154

Fig. 7 Column X1-Y1 at 1st ﬂoor with concrete crushing and rebar buckling

4-D22

4-D19

unit in mm

1250

1150
450

10-D19hoop φ9@250
750

4-D22+6-D19
hoop φ9@250

600
220

220

3-D19
750

220

220
600

450
horizontal sectionof column

4-D22

vertical sectionof beamhorizontal sectionof column(a) Beam-column joint at 7F (X5-Y4)

vertical sectionof beam(b) Beam-column joint at 5F (X5-Y4)

4-D22+8-D19
hoop φ9@250

650

750
unit in mm

Column at 3F (X5-Y4)
Fig. 8 Detail of a typical SRC section of columns in Frame Y41155

Fig. 9 Shear failure of exterior column in Y4 frame

9th floor

8th floor

7th floor

6th floor

5th floor

4th floor

X5

X4

Fig. 10 Joint shear failure of beam-column joints

1156