Prepared By: Sarah Bettinger
Occupancy: Unknown
Year Built:
Height: 42 ft
Number of stories: 4
Stories below ground: unknown
Size:
Original Code: IS:1893-1984 (also Sikkim Building Construction Regulations of 1991?)
Modification: Unknown
Year Modified:
Code of Modification:
Lateral Load System: Frames with Masonry Infill
Other Load System:
Vertical Load System: One-way slab and beams with columns
Other Vertical Load System:
Foundation : Unknown
Other Foundation :
Country: India
State: Sikkim
City: Singtam
Street: Main Bazaar Street
Latitude: 27.13859
Longitude: 88.393494


Building at Singtam

Earthquake Information

 

 

Earthquake Date 40804
Moment Magnitude 6.9
Epicentral Distance 300
Local Intensity MMI
Site Description
PGA Lateral 0.1 (g)
PGA Vertical None (g)
SaT
Ground motion recording stations Earthquake motions were recorded at Gangtok and Siliguri by strong motion accelerographs operated by DEQ, IIT Roorkee. The PGA values recorded at these locations are 0.15g and 0.20g, respectively (Rai, 2012).
Distance to station None
Station Latitude None
Station Longitude None
Ground Motion Summary The US Geological Survey (USGS) indicates that the earthquake was located at 27.723N, 88.064E with a focal depth of 19.7km, in the India-Nepal border region. The quake occurred at the boundary between the India and Eurasian plates, in a region known for seismic activity between the Main Boundary Thrust (MBT) and the Main Central Thrust (MCT).

 

Damage Information

 

 

Performance summary

The lower story of the building was extensively damaged. The upper floors showed less external damage, but showed significant deformation, column damage and joint failure.

Damage state description

The columns in the front most frame yielded, showing severe damage to reinforcing bars and concrete, and significantly shortening the columns. Complete separation of the upper stories from the first story at the column-beam joint was documented in the back of the building. The entire structure deformed, displacing from the original column at the first story.

Summary of causes of damage

1. The lower story had all open bays except one frame with a wall, causing soft/weak story effects. 2. On the lower story in the one frame with a wall, the partition walls did not continue all the way to the ceiling, causing short column effects in the ground story frame columns. 3. The columns in the front most frame yielded, appearing to have undergone tremendous yield due to buckling. 4. The entire structure deformed and displaced at the first story from the original grid pattern. 5. The shortening of the front columns at their failure led to the separation of the upper stories from the ground-level columns in the back of the building.

Observed Design and Construction Characteristics

 

Construction Quality

MaterialsNotesContribution to Damage
Concrete Typically poor quality concrete in the region; Hand mixed concrete
Reinforcing steel Mix of smooth bars and cold twisted bars in column vertical steel

ExecutionNotesContribution to Damage
Conveyance/placement of concrete Hand mixed concrete
Rebar
Field variance with design documents
OtherNotesContribution to Damage
Other Factors Construction Quality

Configuration

Plan IrregularitiesNotesContribution to Damage
Torsion Entire structure deformed and displaced at the first story from the original grid pattern.
Perimeter boundary Corner columns most damaged and deformed
Diaphragm
Out-of-plane offsets in lateral resisting system
Non-orthogonal systems

Vertical IrregularitiesNotesContribution to Damage
Soft story Ground floor open for restaurant; all open bays in shorter direction except one frame with a wall.
Weak story Ground floor open for restaurant
Geometric variablility of lateral resisting system
In-plane discontinuity of lateral resisting system Infill walls above, absent in lowest floor
Mass distribution Uniform
Setback
Change in stiffness

OtherNotesContribution to Damage
Other Factors Configuration

Lateral Load Resisting System‐General

StrengthNotesContribution to Damage
Overall lack of strength

StiffnessNotesContribution to Damage
Extreme Flexibility

Load PathNotesContribution to Damage
Collectors/Struts
Anchorage of nonstructural elements
Out-of-plane capacity of walls Infill walls behaved as unintended lateral load resisting system
Diaphragm chords
Diaphragm openings

OtherNotesContribution to Damage
Other Factors Lateral Load Resisting System-General

Lateral Load Resisting System‐Frames

ColumnsNotesContribution to Damage
Shear strength
Flexural strength
Axial load ratio Columns in the front most frame yielded, appearing to have undergone tremendous yield due to buckling
Vertical load columns drift capacity
Interference of frame action by infill Short column effects at columns with partial height infill at first story.

BeamsNotesContribution to Damage
Strength relative to columns Strong Column, weak beam behaviour
Shear controlled behavior
Continuity of longitudinal reinforcing Poor conitunity and detailing of bars development into joints.
Loss of vertical capacity
Interference of frame action by infill beams

JointsNotesContribution to Damage
Interior Poor detailing
Exterior Poor detailing
Corner Poor detailing

OtherNotesContribution to Damage
Other Factors Lateral Load Resisting System-Frames

Lateral Load Resisting System‐Shear Walls

ShearNotesContribution to Damage
Diagonal tension/compression
Sliding Shear
Flexure/shear

FlexureNotesContribution to Damage
Compression zone buckling capacity
Discontinuity of wall
Boundary reinforcing fracture/buckling
Boundary Reinforcing at openings

OtherNotesContribution to Damage
Other Factors Lateral Load Resisting System-Shear Walls

Lateral Load Resisting System‐Infills

InfillsNotesContribution to Damage
Unreinforced
Interference with frame action Partial height infill caused short column effects at frame columns in ground floor.
Out of plane
Attachment to framing

OtherNotesContribution to Damage
Other Factors Lateral Load Resisting Systems-Infills

Lateral Load Resisting System‐Other

FoundationsNotesContribution to Damage
Liquefaction
Pounding
Surface Rupture

OtherNotesContribution to Damage
Pile/Pier tension capacity

MiscellaneousNotesContribution to Damage
Spread footing capacity No foundation failure observed
Other Factors Lateral Load Resisting Systems-Other-Foundations

OtherNotesContribution to Damage
Other Factors Lateral Load Resisting Systems-Other-Misc

Repair and Retrofit Information

 

Type of Retrofit or Repair

None (demolished/abandoned)

Other Retrofit or Repair

Performance Level

Unknown

Hazard Level

Unknown

Retrofit or Repair Code

Unknown

Other Retrofit or Repair Code

Lateral Analysis

Unknown

Other Lateral Analysis

Design Strategy

Retrofit Summary

References

 

http://www.eeri.org/wp-content/uploads/Sikkim-EQ-report-FINAL_03-19.pdf
Murty, C. V. R. and Sheth, A., ed. The Mw 6.9 Sikkim-Nepal Border Earthquake of September 18, 2011. Learning from Earthquakes. EERI Special Earthquake- February 2012.


http://db.concretecoalition.org/static/data/6-references/INDI003_Reference_1.pptx
Sheth, A. and Murty, C. V. R. "Damage Patterns in Sikkim 2011 Earthquake." Earthquake Engineering Research Institute. Oakland, California. 25 June 2012.


http://www.nicee.org/Sikkim_EQ_2011_Slide.pdf
National Information Center on Earthquake Engineering, 2011. 2011 Sikkim Earthquake: Effects on Built Environment & a Perspective on Growing Seismic Risk (Accessed: July 10, 2012).


http://www.nicee.org/current%20Science.pdf
Rai, D. C., et. al., 25 May 2012. The M 6.9 Sikkim (India-Nepal Border) earthquake of 18 September 2011, Current Science , vol. 102, no. 10, 1437-1446 .


http://earthquake.usgs.gov/earthquakes/eqinthenews/2011/usc0005wg6/
United States Geological Survey (USGS), 2012.Magnitude 6.9- India-Nepal Border Region (Accessed: 25 July 2012).