Proceedings of the International Symposium on Engineering Lessons Learned fromthe 2011 Great East Japan Earthquake, March 1-4, 2012, Tokyo, JapanEVALUATION SYSTEM OF SESMICCAPACITY FOR BUILDING FOUNDATIONSAND CASE STUDIES ON BUILDINGS IN
SENDAI CITY
Osamu KANEKO1, Shoichi NAKAI2, Mikio FUTAKI3 and Hiroshi ARAI4
1

Senior Researcher, Research Institute of Technology, Toda Corporation,
Tokyo, Japan, osamu.kaneko2@toda.co.jp
2
Professor, Department of Urban Environment Systems, Chiba University,
Chiba, Japan, nakai@faculty.chiba-u.jp
3
Director, Tsukuba Building Research And Testing Laboratory, Center for
Better Living, Tsukuba, Ibaraki, JAPAN, futaki@tbtl.or.jp
4Senior Researcher, Building Department, National Institute for Land andInfrastructure Management, MLIT, Tsukuba, Ibaraki, JAPAN, arai-h92ta@nilim.go.jp
ABSTACT: The authors have developed a systematic approach for the seismic
evaluation of building foundations. The proposed approach allows structural engineers tochoose between an empirical based, relatively simple method, and a theoretical, more
rigorous method involving numerical seismic response analysis, as may be appropriate
for the seismic evaluation of foundations. Applicability of this approach is verified in thecase study of some buildings in Sendai city, which suffered damage to their foundations
during the 1978 Miyagiken-oki Earthquake and the 2011 Great East Japan Earthquake.
Key Words: Building Foundation, Seismic Evaluation, Great East Japan Earthquake

INTRODUCTION
Following the 1995 Hyogoken-Nanbu Earthquake, it has been a common practice in Japan to conduct
seismic evaluation of existing buildings. However, evaluation of the seismic capacity of foundations
and soils supporting existing buildings has been generally disregarded because the regulations
governing the practice do not provide adequate procedure for this purpose. Meanwhile, during the2011 Great East Japan Earthquake, there were several cases reported where operation or regularoccupation of buildings had to be suspended because of the damage to foundation supporting thebuilding.
The authors have studied the requirements for foundations and supporting soils to provide
resistance against the design earthquakes associated with the level of performance, and evaluatedanalytical methods to estimate seismic capacity of foundations. As a result, a systematic procedure toevaluate the seismic capacity of building foundations necessary to maintain structural function, even1200

after major earthquakes, is evolving.
This report presents a basic procedure for seismic evaluation of existing building foundations
and discusses its applicability to some buildings in Sendai city damaged during the 2011 Great East
Japan Earthquake.
SEISMIC EVALUATION OF EXISTING FOUNDATIONS
In general, the Japanese structural design codes do not require the building foundations to remain
undamaged under extreme seismic events. This is based on the premise that damage to building
foundations is unlikely to cause the risk to life from catastrophic collapse of superstructure. However,
it is possible that the failure of foundation system may have resulted in life loss in some cases where
the soil liquefaction was a factor in the collapse of superstructures during the 1995 Hyogoken-Nanbu
Earthquake. The authors feel that a thorough seismic evaluation of existing buildings should include
an examination of the foundation, and assessment of the capability of the soil beneath the foundation
to withstand seismic forces. Even when the superstructure has sufficient seismic capacity, a tiltedbuilding owing to foundations damage will result in loss of function and property value. Besides, suchbuildings will become obstacles to emergency evacuation.
Thus, it is necessary to conduct seismic evaluation of superstructures as well as foundations toensure required performance. Authors have taken this initiative to propose the seismic evaluation
procedure so that the seismic evaluation of building foundations can be performed routinely inpractice.
This evaluation procedure is expected to be applicable to the buildings and ground conditions
mentioned as follows:
1) Buildings for which the seismic evaluation of superstructure has been conducted in advance. It
is not expected to be applicable to building that have collapsed or tilted due to the foundation
damage. The operational performance can be guaranteed by examining as a total system
consisting of the foundation and the superstructure.
2) Buildings designated as emergency hospitals and evacuation facilities, and those facing
designated evacuation routes. In these cases tilting of buildings can jeopardize their function,or may become a hazard to mass evacuation.
3) Sites where liquefiable soils or very soft deposits exist, regardless of the building type. In
these soil conditions, total failure of supporting soil may cause the building to overturn.
In addition, the seismic design of foundations has not been considered in most buildings
constructed before 1980s in Japan. It is reported that a considerable number of those buildings weredamaged due to foundation failure during the 1995 Hyogoken-Nanbu Earthquake. Similar trend can be
expected for Tohoku area in relation to the 2011 Great East Japan Earthquake. Need for seismic
evaluation of such building foundations is anticipated as the recovery and reconstruction efforts
continue.
Seismic evaluation of buildings including foundations will also provide the building owners withadequate understanding of the expected performance of their buildings under a design earthquake,considering functional as well as safety aspects.
PROPOSED PROCEDURES FOR SEISMIC EVALUATION OF FOUNDATIONS
The target performance level of foundations is to ensure safety of occupants without failure of thebuildings and/or to maintain them in operational condition such that excessive tilt and/or displacement1201

do not impact functionality. Three nonstructural performance levels for buildings defined in theseismic evaluation procedure are shown in Table 1. In consideration of the importance and function of
the building, professional engineers can choose an appropriate level of performance corresponding toa design earthquake from Table 1.
Structural damage conditions of foundation members associated with corresponding performancelevels in Table 1, which are called limit states, are described in Table 2. It is noted that the relationshipbetween the damage of foundations and possible excessive settlement and/or tilting of foundations is
not clarified, for which further study is necessary.

Table 1. Nonstructural Seismic Performance Levels of Buildings
A:

B:

Operational Level

Immediate Occupancy Level

All basic structural functions arepreserved. Continued use ispossible without repairs, and no
excessive
displacement
anddeformation has occurred.

Continued use of the building
is possible if feasible repairs
but
no
are
performed,
excessive displacement anddeformation has occurred.

C:Life Safety and Collapse
Prevention Level
Entire structure is still stable
despite the loss of bearing
capacity, and overturning or
collapse has not occurred.

Table 2. Correlation between the Level of Performance and the Relevant Limit State of Foundation

Foundation
Soil

Foundation
Members (pile,foundation
beam, pile cap)

A

B

C

Bearing capacity anddisplacement does notexceed ther yield levelvalues by more than two
fold, both in push andpull directions.

Bearing capacity anddisplacement do not
exceed half of theirultimate values in bothpush and pull directions.

Bearing capacity as well
as displacement does notexceed their respective
ultimate values in pushand pull directions.

Yield bending moment is
not exceeded in morethan half the members,
andallowable
shear
strength not exceeded
anywhere in all members.

Yield bending is notexceeded in all members,
ultimate moment is notexceeded in half themembers, and ultimate
shear stress is notexceeded in more than
two places.

Moment curvature does
not exceed limit level, or
ultimate moment is notexceeded at two points
along depth, and ultimate
shear strength is notexceeded in more thanhalf of members.

PROPOSED EVALUATION PROCEDURE
The authors propose a seismic evaluation procedure for building foundations consisting of thefollowing components:
1) Preparatory Decision 1: Verification of the requirements of target building
2) Preparatory Decision 2: Choice of the evaluation method

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3) First Level Seismic Evaluation: Estimation by the indices, namely seismic index Isf and thejudgement index Is0f, based on the damage investigations in past earthquakes
4) Second Level Seismic Evaluation: Assessment based on static analysis5) Special Evaluation: Assessment based on dynamic analysis, finite element method or other methods
depending on particular conditions
6) Considerations of the need and suitability of seismic retrofitting
The proposed approach allows professional engineers to choose an adequate method for the seismic
evaluation of foundations, which can be either an empirical, relatively simple method or analytical,
more sophisticated methods such as numerical seismic response analysis and FEM analysis.
Professional engineers perform the seismic evaluation of building foundations following aprocess shown in Figure 1. Prior to conducting a seismic evaluation, the necessity for the seismic
evaluation is judged in the Preparatory Decision 1. Then, a suitable method should be chosen
depending on the building conditions in the Preparatory Decision 2. Possible judgment examples atthis stage are proposed in Table 3. For instance, the First Level Seismic Evaluation can be applicablefor the buildings with shallow foundation or with basement since better near surface ground conditionis expected in these cases. On the contrary, the buildings on pile foundations in very soft groundcondition, or in liquefiable ground condition, should have Second Level Seismic Evaluation for a moredetailed assessment.
The First Level Seismic Evaluation has been proposed based on the seismic indices derived fromthe failure investigations following the 1995 Hyogoken-Nanbu Earthquake and the required bearing
capacity of building foundations (Maruoka et al 1999). As an empirical method, the possibility of the
failure of foundation can be roughly estimated in this evaluation. However, no details about how the
deficiencies are distributed within the foundation system are provided by this method. The results ofevaluation in this method may not necessarily lead to a definite conclusion concerning the requirement
for taking further steps. However, professional engineers can employ more sophisticated dynamic
analysis, or static non-linear (pushover) analysis, depending on their judgment concerning structural
conditions and the expected improvement in the accuracy of performance evaluation by such analyses.
Figure 2 shows possible analytical models for static analysis of pile foundations in the Second
Level Seismic Evaluation. Analytical results from such models should be compared to the level of
performance in each limit states shown in Table 2. Possible deficiencies in the foundation can beevaluated in more detail in this manner, and one can assess the results to see if they meet the expected
performance. Professional engineers can design adequate seismic retrofit to meet performancerequirement.
In general, there are two values required for computing pile capacity, namely the lateral load at
the pile head and the stresses generated by differential movement of soils. The differential movement
in soils can be evaluated from the ground response analysis under site-specific design earthquake.
The seismic lateral load at the pile head should be calculated in the following manner dependingon the targeted level of performance:
1) To ensure that the foundation will not fail before the superstructure, the bearing capacity should be
sufficient to resist forces transferred from the superstructure under design earthquake.
2) To ensure that the foundation will not collapse under the largest expected earthquake, the bearing
capacity should be adequate to resist forces obtained from the response analysis of superstructure
under site-specific largest expected earthquake.
In the case of special conditions, such as buildings near slopes, rigorous method, for instance FEM

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analysis, may be required for proper estimation of seismic forces. Furthermore, dynamic analysis or
combined analysis taking soil-pile-structure interaction into account may be necessary. In the seismic
evaluation procedure presented, these methods are indicated as appropriate. Choice of an appropriate
method is crucial depending on design conditions; this process is regarded as Special Evaluation.
If the results of either the Second Level Seismic Evaluation or the Special Evaluation do not meetthe level of performance, a seismic retrofit will possibly be required. In assessing the retrofitting
process, it is necessary to consider installation aspects under specific site conditions.

START

Preparatory
Decision1
ChooseStrict Analysis

Necessary

Preparatory
Decision2

Unnecessary

END
Lack of
Information

Not Execute

Additional
Investigation

Choose Schematic Evaluation

Unsuitable

ExecuteGo to Preparatory Decision2

1st Grade Evaluation
Isf

Isf≧Isf0

Comparison
Isf and Isf0

Isf :Seismic Index of Foundations
Is0f :Judgment Index of Foundations

Isf <Isf0

Selection of
Evaluation Method

Choose Separate Evaluation

Choose Preparatory Decision2

2nd Grade Evaluation
Capacity
Capacity≧DemandComparison
Demand and Capacity

Separate Evaluation
Capacity

Capacity<Demand
Capacity<Demand

Review ofRetrofit of Foundations

Comparison
Demand and Capacity
Capacity≧Demand

END

Fig. 1 Flow Diagram for the Seismic Evaluation

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Axial Force
Rigid Beam

Differential
Movement of Soils

Lateral Load
Pile Cap Joint
Footing Beamor Rigid Beam

Pile
Lateral Soil Spring

Foundation Structure Model

Single Pile Model

Fig. 2 Analytical Models to evaluate the Seismic Capacity of Foundations

Table 3 Possible Options in the Preparatory Decision 2
Ground Condition

First level
Evaluation

Second Level
Evaluation

Special
Evaluation

Stable◎×○

Unstable××◎

Pile Foundation

Stable◎◎○with basement

Unstable×△◎

Stable○◎○Unstable△◎○Foundation Type
Shallow Foundation

Pile Foundation
without basement

Slope
×
△
◎
◎:Recommended，○:Usable，△:Usable but not recommended，×:Not capable
CASE STUDIESThe proposed procedure was applied in the following buildings damaged during the 2011 Great East
Japan Earthquake.
The seismic evaluation was conducted for three apartment buildings located in Sendai city
(Sugimura and Oh-oka 1981, Shiga 1980, AIJ 2011a). General information on the upper structures andfoundations are given in Table 4. Since these buildings were constructed before 1980s, no effective
seismic design was implemented. Soil profiles are shown in Figure 3. Ground condition can beconsidered relatively stable. It is anticipated that the liquefaction resulting in total bearing capacity offoundation would not occur even though partial liquefaction may occur.
The investigation shows that all of the pile foundations of these buildings had been damaged
during the 1978 Miyagiken-oki Earthquake. In building-A, more than half of the piles had been failed
either in compression or in shear at pile head. In building-C, although no tilting was observed, thecorner piles suffered similar failures near pile head. Building-B, adjacent to the building-A, also
showed no tilting while some cracks were identified in some of the piles from a partial investigation.

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Subsequently, total retrofitting was carried out for the foundation of building-A. One of thebuilding foundations was converted from the pile foundation to the shallow foundation. Elsewhere, all
the failed pile heads were reinforced by means of steel plates, including corner piles of building-C.

Table 4 General Information on Upper Structures and Foundations
Structure

Number of
StoriesYear ofConstruction

Pile Type

Pile Diameter

A

SRC

11

1978

Precast Concrete Pile

600mm

B

RC

5

1977

Precast Concrete Pile

400mm

C

SRC

14

1976

Precast Concrete Pile

500-600mm

SPT-N value0

10 20 30

40

SPT-N value
50

0

0

10

20

30

40

50

0
Silt

Silt

Sand
5

Humss

5

10

Depth (m)Depth (m)Sandy
GravelSilty
Gravel
15

Sand

Sand

15
Silt
Sand

Silty
Gravel

20

10

20

Silt

Gravel25

Site of Buildings-A and B
Fig. 3Site of Building-C

Soil Profiles(Sugimura and Oh-oka 1981, Shiga 1980)

Buildings-A and B have remained occupied without deficiency after the 2011 Great East Japan
Earthquake. In case of building-C, although upper structure consisting of columns and beams did notindicate any structural damage, it has tilted significantly and is designated as deficient for immediate
occupancy. It should be noted that foundations of these buildings have not been investigated following
the 2011 Great East Japan Earthquake.
Seismic evaluation of these building foundations was conducted by the proposed procedure.
Evaluated index Isf from the First Level Seismic Evaluation are shown in Table 5. The Is0f index valueof 0.8 is assessed based on the 1995 Hyogoken-Nanbu Earthquake, The index value requires to becorrected for the maximum acceleration, which is 250.9 gal comparing to 350 gal (considered to be a1206

benchmark) for the 1995 Hyogoken-Nanbu Earthquake. Therefore, the Is0f index value for the 1978
Miyagiken-oki Earthquake would be 0.8*250.9/350=0.57. The three building foundations are
categorize as “not good” considering seismic capacity with Isf/Is0f <1.0, which is in agreement with theactual failure situation that occurred at the 1978 Miyagiken-oki Earthquake. However, no details ofdamage condition are represented in this method.
Table 5 Results of The First Level Seismic Evaluations of Building Foundations in Sendai
Isf ValueA
A (After Retrofitting)
B
C

0.33
0.82
0.28
0.26

Is0f Valuefor the 1978
Earthquake
0.57
0.57
0.57

Evaluation
Results
not good
not good
not goodIs0f Valuefor the 2011
Earthquake
0.73
0.73
0.73

Evaluation
Resultsgood
not good
not good

Second Level Seismic Evaluation was conducted for buildings-A and B considering the observed
seismic motion at the 1978 Miyagiken-oki Earthquake for estimating pile head load and differential
deformation of soils. Evaluated results indicate that the immediate occupancy will be unlikely due tothe pile head yield in building-A, whereas the foundation of building-B may maintain its function
without significant damage. From these results, the foundations of building-A were evaluated to beunsatisfactory at performance level B (Immediate occupancy level), while building-B is regarded
satisfactory at level B. The difference of the damage mainly depends on axial force applied to piles by
the seismic motion.
Next, retrofitted foundation of building-A was considered for First Level Seismic Evaluation. The
Isf index value after retrofitting is estimated as 0.82 and the Is0f index value for the 2011 Great East
Japan Earthquake is assessed as 0.73 (corrected for maximum acceleration of 317.7 gal observed in
the same building during the 1978 Miyagiken-oki Earthquake (AIJ 2011b). The ratio of Isf to Is0f
becomes 0.82/0.73=1.15 and the foundation is categorized as "good".
Through the above-mentioned case studies, the proposed procedure shows results consistent withobservation, indicating its applicability for seismic evaluation of building foundations.
CONCLUSIONSThis paper describes the procedure for the seismic evaluation of building foundations with a focus on
maintaining buildings in operational level of performance. This procedure allows professional
engineers to choose an appropriate method depending on the level of performance and local site
condition. Applicability of this seismic evaluation procedure has been verified through case studies onbuildings that suffered foundation damage during past earthquake.
Preliminary observations following the 2011 Great East Japan Earthquake indicate that there areseveral buildings became functionally deficient for occupation due to foundation damage even though
the superstructure did not suffer significant damage. These observations indicate the importance ofassessing the seismic capacity of building foundations. Authors hope that the seismic evaluation ofbuilding foundations following the procedure proposed herein will be more common in Japan.

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ACKNOWLEDGMENTS
This report is an outcome of the efforts of the research committee for recommendations for seismic
evaluation of existing building foundations funded in part by the Center of Better Living in Japan. The
authors would like to express appreciation to all the members of the committee.
REFERENCES
Maruoka, M. et al(1999). ”A Proposal for Seismic Capacity Evaluation of Existing Building
Foundations.” AIJ Journal of architecture and building science, No.8, 85-90 (in Japanese)
SUGUMURA, Y. and Oh-oka, H.(1981). “Report on the Damage of Precast Prestressed Concrete Piles
during Off-Miyagi Prefecture Earthquake.”, Kenchiku Kenkyu Shiryo, No.31(in Japanese)
Shiga, T. (1980). “Earthquake Damage of Concrete piles.” JCI Concrete Journal, , Vol.18, No.8,
14-21(in Japanese)
Architectural Institute of Japan(AIJ) (2011a). ”Preliminary Reconnaissance Report of the 2011
Tohoku-Chiho Taiheiyo-Oki Earthquake.” 97-98(in Japanese)
Architectural Institute of Japan(AIJ) (2011b). ditto, 61(in Japanese)1208