PERFORMANCE BASED EARTHQUAKEEVALUATION OF SCHOOL BUILDING IN
SRILANKA
Chandima Kularatne*
MEE07153

Supervisor: Dr. Tomohisa Mukai**

ABSTRACTThis study quantifies the seismic vulnerability of typical three storied class room building located in
SriLanka. A significant feature of this reinforced concrete frame building is that this was not designed
for seismic effects. Besides, there are some infill brick walls also.
A methodology given in “Guidelines for Seismic Performance Assessment of Buildings”( ATC-58 )was followed as it was expected to study consequences of earthquake. As per ATC-58, intensity based
assessment was considered for Hazard Analysis while the Structural Analysis was carried out toobtain engineering demand parameters (EDP) such as story drift and story acceleration. Besides, aDamage Analysis was carried out not only for structural members but also for non-structural members.
Pushover analysis was done in order to define damage states of the structural while Loss Analysis was
carried out to quantify the direct economic loss.

1.INTRODUCTION

School buildings have been considered as post-disaster buildings or special buildings in many
countries considering its’ role after an earthquake. As per HAZUS-MH MR3 Technical Manual also,
school buildings are considered as essential facilities. Therefore, it is it is very important to design
school buildings to withstand seismic effects.
However it has been realized that yet non of the school buildings in SriLanka have been
designed to mitigate seismic effects. Therefore, it is important to investigate the seismic vulnerabilityof at least a single school building in SriLanka. A three storied building was selected forinvestigations because this is the most typical building all over the country. In order to achieve above
objectives, a methodology given in “Guidelines for Seismic Performance Assessment of Buildings”(ATC-58) developed by Advanced Technology Council was used. Accordingly, an assessment of
performance capability was carried out for this building.
The software STERA 3D (Dr.T.Saito,2005) was used to perform pushover analysis andnonlinear response-history analysis. Pushover analyses were used to define the story capacity limit
states of the modeled structure. Pushover analyses were run several times to determine quantitative
limit states of inter-story drift. Nonlinear response-history analysis was used to determine theengineering demand parameters. A simple calculation method was used for loss calculations. The
repair method was proposed as per in the context of SriLanka and the prevailing rates were used forcost calculation.

* Civil Engineer(Structural Designs),Ministry of Education, Government of Sri Lanka.
** Research Engineer at International Institute of Seismology and Earthquake Engineering

12.BUILDING OVERVIEW

Even though this building has been designed for wind loads, it can be proved that the wind load isvery small compared to the seismic load. The designed strength of concrete has been considered as
20MPa. Since this is cube strength of concrete, it was converted into cylindrical strength as 16Mpa.
The strength of all the main reinforcement steel is 460Mpa while the strength of shear reinforcementis 250Mpa. Besides, the compressive strength of bricks has been estimated as 3Mpa as quality of thebricks are poor. The compressive strength of mortar has been considered as 4Mpa. The detail of thisbuilding is shown in Figure 1. A size of 300mmX375mm columns are located from first floor to third
floor level and corner columns from third floor to roof level. Size of the other columns from third
floor to roof level are 225mmX375mm. Size of all the beams spanning in longer direction of thebuilding
is 225mmX22mm. However, the size of beams spanning shorter direction is
300mmX650mm except roof level. The size of beams spanning in shorter direction at roof level is
225mmX450mm. Besides, there are some masonry infill walls spanning in the shorter direction. Hereafter, the longer direction of this building was considered as X-X direction while the other direction
was considered as Y-Y direction.

Figure1. Detail of the building

3.HAZARD ANALYSIS

As we are aware, earthquakes can also occur within the single tectonic plate and are referred to as
intraplate earthquakes. SriLanka is also located within one of such area know as Indo-Australia plate.
Intraplate regions have been historically described as areas of low to moderate seismic hazard. The
effects and risks involved with intraplate earthquakes have been studied, but not yet fully understood.
Especially in SriLanka, lack of reliable data on past earthquakes hinders the study on seismicity
around SriLanka. However, as per available records, it is evident that SriLanka is not a seismicallyinactive country but the earthquake could occur at long recurrence period
According to the available data, it was suggested for Colombo an earthquake of magnitude
close to ML=6 on Richter scale with a return period of 200-400 years; a design acceleration of
0.2g(196cm/s2) is considered as the horizontal component of the earthquake while the verticalcomponent is neglected at this stage. Besides, the attenuation relation developed by Fukushima andTanaka was applied for earthquake of ML=6 on Richter scale and a site of 5km away from theepicenter. It was found that the Peak Ground Acceleration as 186.4 cm/s2 which is quite similar tosuggested acceleration 0f 0.2g. Therefore, it was decided to follow intensity based assessment with aacceleration of 0.2g (196cm/s2).

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4.STRUCTURAL ANALYSIS

Since this is an existing structure, structural designs were not carried out. However, the failure modesof the building were investigated and it was revealed that all the beams and columns failed because offlexure. Besides, it was revealed that the failure modes of the columns and beams are columns
governed by the flexural beam and flexural column in X-X and Y-Y directions respectively.
Displacement control pushover analysis was used for this study. First of all, a target
displacement for the structure was established as 1/50. The contribution of the infill walls toseismic resistance was also considered in this study. The effect of P-Delta was not considered
for the analysis because of the low rise building.
According to pushover analysis, it was revealed that the soft-first story mechanism would
be formed in Y-Y direction and more interestingly it was observed that the obtained failure modes
were agreed with that obtained from manual calculations
Since it was observed several infill masonry walls, an attempt was made to develop ananalytical model. The shear resistance at cracking, maximum and ultimate was calculated as per
Kabeysawa, T., Mostafei, H. It was noticed that the respective displacements are almost similar inanalytical model and results of pushover analyses.
Nonlinear Response-History Analysis was used to determine the engineering demandparameters(EDP) of the structure with 5% damping under suite of 11earthquake ground motions. The
suite of earthquakes was scaled to spectral acceleration of 196gal at the period of 0.903sec and0.522sec because it was expected to analyze the structure for both directions.

5.DAMAGE ANALYSIS

According to ATC-58, it is necessary to assess the possible distribution of damage to structural andnonstructural components using the response data from the structural analysis together with data on
the building configuration. However, the damage analysis of this study was concentrated mainly on
structural components and masonry infill walls.
Accordingly the structural damage states such as slight, extensive and complete of structural members
and masonry walls were classified based on the pushover analysis results. The damage states areshown in Figure.2. Besides, the repair methods for each damage state were studied.
RELATIONSHIP FOR FORCE AND DISPLACEMENT FOR
MASONRY WALLSMOMENT-CURVATURE RELATIONSHIP FOR REINFORCED
CONCRETE MEMBERS
Ductility Factor=4(4θ)

Extensive Structural
Damage State - Crack width
0.2mm-1mm, Extensive
Cracking, Yielding of
Slight Structural Damage
State Crack width<0.2mm
Curvature

Complete Structural
Damage State - Severe
Cracking & Spalling,
Buckling of Reinforcement

EXTENSIVE STRUCTURALDAMAGE STATE - MAX.
SHEAR RESISTANCE
F o rceM oment

θ

SLIGHT STRUCTURALDAMAGE STATE CRACKING INITIATECOMPLETE STRUCTURAL DAMAGE
STATE - ULTIMATE SHEAR RESISTANCE
Displacement

Figure 2. Damage states of structural members and infill masonry wall

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It was observed that all most all of the beams spanning in X-X direction reached thecomplete damage state in case of pushover analysis was performed in X-X direction. Thus, it wasdetermined that the base shear coefficient of this structure at X-X direction is 0.08 and this is not
sufficient even for regions where seismicity is very low. Besides, story drift at respective damage state
was almost same for second and third story. However, it was somewhat different in roof level and outof thirty six(36) beams spanning X-X direction, only twenty beams reached complete damage state.
Similarly, pushover analysis results on Y-Y direction were also studied. It was found that
only some of the columns reached these damage states. The beams spanning Y-Y directions did notreach even the slight structural damage state. Even at second story only sixteen columns had reached
the complete structural damage stage. However, it was found that the base shear coefficient of Y-Y
direction is 0.245, as such that is sufficient enough for low seismicity countries like SriLanka.
In addition, it was decided to define structural performance level of this building based on
Prestandard and Commentary for the Seismic Rehabilitation of Building published by FEMA(FEMA356). Therefore, an attempt was made to represent the probable Structural Performance Levels of thisbuilding in terms of top drift. According to the results of pushover analysis, the relationship of top
drift versus base shear coefficient for both directions were drawn and shown in Figure 3.

9.E-02TOP DRIFT ANGLE-BASE SHEAR COEFFICIENTFOR X-X DIRECTION
Damage states

Reparability Limit

sequence of roof3rd story.
Damage states
sequence of 3rdstory-2nd story .
Damage states
sequence of 2ndstory-1st story .

8.E-02

6.E-02

IMMEDIATE
OCCUPANCYPERFORMANCE
LEVEL

5.E-02Q /W

LIFE SAFETYPERFORMANCE
LEVEL

4.E-02

Reparability Limit

2.5E-01

Damage states
sequence of roof - 3rdstory.

2.0E-01

Damage states
sequence of 3rd story2nd story.

Q /W

7.E-02TOP DRIFT ANGLE-BASE SHEAR COEFFICIENT
FOR Y-Y DIRECTION
3.0E-01

1.5E-01

COLLAPSE
PREVENTIONPERFORMANCE
LEVEL

1.0E-01

3.E-02
2.E-02

5.0E-02

LIFE SAFETYPERFORMANCELEVELCOLLAPSE
PREVENTIONPERFORMANCE
LEVEL

Damage states
sequence of 2nd story1st story.

IMMEDIATE
OCCUPANCYPERFORMANCE
LEVEL

1.E-020.E+000.0E+00

5.0E-03

1.0E-02 Ri 1.5E-02

2.0E-02

0.0E+00
0.0E+00

2.5E-02

5.0E-03

1.0E-02

1.5E-022.0E-02

2.5E-02

Ri

Figure 3. Damage sequence of members X-X and Y-Y direction
In addition to concrete frame structure, behavior of the masonry infill walls were studied
according to the above defined performance level. Results of pushover analysis were used to identify
the top drift when masonry walls reached respective performance level and which is depicted in
Figure 31.
Accordingtothedefinedperformance level of building, all the masonry
TOP DRIFT ANGLE-BASE SHEAR COEFFICIENT
walls at first story level will be collapsed before
FOR Y-Y DIRECTION
3.0E-01
the Immediate Occupancy Performance Level.
2.5E-01
All the masonry walls at second story level will
2.0E-01
reach extensive damage stage before theImmediate Occupancy Performance Level while
1.5E-01
it will reach complete damage state at the Life
1.0E-01
Safety Performance Level. However, masonry
5.0E-02
walls at third story level will be reached only
slight structural damage state.
0.0E+00
Q/W

Damage states
sequence of walls atroof - 3rd floor.

LIFE SAFETYPERFORMANCELEVELCOLLAPSE
PREVENTIONPERFORMANCE
LEVEL

Damage states
sequence of walls at
3rd story-2nd Story.
Damage states
sequence of walls at
2nd story- 1st story
level.

IMMEDIATE
OCCUPANCYPERFORMANCE
LEVEL

0.0E+00

5.0E-03

1.0E-02

1.5E-022.0E-02

2.5E-02

Ri

Figure 4. Damage sequence of masonry walls

4Subsequently, the engineering demand parameters (EDP) obtained from nonlinear responsehistory analysis were used to study the vulnerability of this structure. It was proven that the X-X
direction of the building is the most vulnerable. It was observed that the maximum response story driftof the X-X direction in the second floor did not exceeded the life safety performance level for thesuite of earthquake. However, it was not exceeded the immediate occupancy performance level incase of maximum response story drift for the suite of earthquakes on Y-Y direction and not even all
the columns in the first story level did reach the extensive structural damage state. It was found thatthe behavior of the second story level is similar to that of first story level.
It was observed that the performance of the third story in both directions is significantly
better than that of first and second story levels. The both, maximum response story drift and minimum
median response story drift in X-X direction was lain within the life safety performance level whilethat of Y-Y direction was lain within the immediate occupancy level. It was observed that none ofcase, all the columns reached the slight structural damage state at third story.

6.LOSS ANALYSIS

Loss analysis was carried out only for structural elements and masonry walls because the cost of
nonstructural elements and facility equipment are less compared to that of structural elements andmasonry walls. Besides, simple calculation was done to determine losses rather than going for more
rigorous analysis such as Montre Carlo type procedures because of time constraints.
The total structure repair cost of each case was calculated by multiplying the total repair
quantity by the unit cost. The total repair quantity was estimated by identifying corresponding step of
pushover analysis to story drift. It was
STRUCTURAL REPAIR COST ACCORDING TO
observed that total structure repair cost would
DIRECTIONbebetweenRs.240,000.00
andRs.2,500,000.00.The average total structure
repair cost is Rs.2,337,550.00. However it waslearnt that the total construction cost of thisbuilding is Rs. 16,000,000.00. Thus theCase 1average repair cost is 14.6% of totalCase 2construction cost.
Case 3
Case 4The variation of total structure repair cost ofCase 5each case with direction of the structure wasCase 6studied to identify which direction contributes
most to the repair cost. The graphs of total
Direction
repair cost versus direction and story are
depicted in Figures 5.
3,000,000

2,500,000

Cost / ( Rs. )2,000,000

1,500,000

1,000,000

500,000

0

X-X Direction

Y-Y Direction

Masonry Walls

Total

Figure 5. Structure Repair Cost According to Direction

7.CONCLUSION

In summary, much knowledge has been gained from the study performed for this report. The behaviorof three storied reinforced concrete frame structure used as a school building located in SriLanka,
exposed to seismic load was studied.

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It was found that the seismic performance of this structure is very poor in X-X direction whilethat of Y-Y direction is adequate. Therefore, even a small magnitude earthquake posed a threat
because of poor X-X direction of the structure. The threat present with the occurrence of small
magnitude earthquake events would most likely cause extensive damage to the structure.
As per FEMA 356, Prestandard and Commentary for the Seismic Rehabilitation of Building,
performance levels of this building were defined using results of pushover analysis. The performancelevels were indicated in the graph of base shear coefficient versus top drift. Accordingly, the inherent
weakness of X-X direction of the structure was illustrated in the performance levels also. Therefore,
these facts lead to a retrofit of the structure and it can be considered as a obligation for future work.
The behavior of masonry walls was studied using analytical model in structural analysis. It
was found that the walls located at first two stories reached the complete structural damage state at
small story drift. However, the behavior of the masonry walls was not studied for in case of out ofplane failure. The loss analysis was carried out for masonry walls also but the repair cost of themasonry walls are negligible compare to that of reinforced concrete structure.
The repair cost of each damage state was calculated based on the rates obtained from a privatecompany in SriLanka. Therefore, total structure repair cost was determined for maximum and meancases of suite of earthquakes. It was found that total structure repair cost in X-X direction would be
Rs.2,,228,000.00 in case of mean response story drift in the X-X direction while that of Y-Y direction
is only Rs.56,000.00.
Considering the above facts, the following suggestions can be made as concluding remarks.
Reinforced concrete shear walls could be provided to enhance the shear capacity in the X-X directionof the building. Besides, it was found that the base shear coefficient in Y-Y direction is 0.25 and it isadequate even for soft-first story structure. In addition, it is necessary to strengthen the infill masonrywall because it was observed that the infill masonry walls reached complete structural damage stateprior to the structure reach immediate occupancy performance level.

8.ACKNOWLEDGEMENTS

My special gratitude to my advisor, Dr. Taiki Saito, Chief Research Engineer at IISEE, who has
guided me from the inception of the course and given me valuable advices on this study.

9.REFERENCES

Abayakoon, S.B.S ,1998, Engineer, Journal of Institution of Engineers, SriLanka, Vol xxviii, No 2,
29-36.
Applied Technology Council, 2007, U.S. Department of Homeland Security, Federal Emergency
Management Agency.
Federal Emergency Management Agency, 1998, Washington D.C.
Federal Emergency Management Agency, 2000, Washington D.C.
Federal Emergency Management Agency, 2003, Washington D.C.
Kabeysawa, T., Mostafei, H., Bulletin Earthquake Research Institute, University of Tokyo, Vol.79,
133-156.
The Japan Building Disaster Prevention Association.

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