The Mansi Apartment Complex was a two-wing structure connected through the stair and elevator core. The ground story was open as a space for parking, and the floors cantilevered out between 1.5m and 2m along the perimeter. Additionally,the upper floors ca...

Prepared By: Sarah Bettinger
Occupancy: Mixed Use
Year Built: 1995
Height:
Number of stories: 11
Stories below ground: unknown
Size:
Original Code: IS:1893-1984, IS:456-78, IS:13920-1993
Modification: none
Year Modified: N/A
Code of Modification: N/A
Lateral Load System: Shear Wallrete
Other Load System: Elevator core formed the shear core in the building, but the diaphragm connectivity and detailing between the two sides of the b
Vertical Load System: Other
Other Vertical Load System: Concrete slab, beams, and columns
Foundation : Other
Other Foundation : Shallow Foundations
Country: India
State: Gujarat
City: Ahmedabad
Street:
Latitude: 23.051303
Longitude: 72.563903


 

Mansi Apartment

Earthquake Information

 

 

Earthquake Date 36917
Moment Magnitude 7.7
Epicentral Distance 240
Local Intensity VII Other
Site Description The city of Ahmedabad is located on the bank of the Sambarmati River and is built on sediments whose thickness varies from about 2km to 4km. A crustal profile indicates that the seismic waves must have propagated through several local basins with low velocity materials, which might have amplified the ground motions (Jain et al., 2002). Collapsed buildings appear to have been built on the path of the old Sambarmati River.
PGA Lateral 0.11 (g)
PGA Vertical None (g)
SaT
Ground motion recording stations The closest recording station was at Bhuj, on hard rock, located slightly north of the Katrol hill fault, and about 80km from the epicenter. The Bhuj station was equipped with digital broadband, analog short period, and strong motion sensors, but the strong motion sensor did not function well during the earthquake. Strong motion recordings were also taken from stations at Ahmedabad, Roorkee, Delhi, Mumbai, Hyderabad, Bangalore, and Goa. A 10-story residential building within the complex of the Regional Passport Office at Ahmedabad that was instrumented at the ground floor was the only ground motion acceleration record available for the event (Jain et al., 2002).
Distance to station None
Station Latitude None
Station Longitude None
Ground Motion Summary The USGS indicates that the earthquake was located at 23.40N, 70.32E with a focal depth of approximately 18km, approximately 70km east of the city of Bhuj, the headquarters of the district of Kuchchh in the state of Gujarat .The imperfectly recorded broadband seismograph from the Bhuj station indicated ground motions at a sustained level for about 85s following the P onset, followed by several minutes of lower level shaking.

 

Damage Information

 

 

Performance summary

The wing with the additional roof loads collapsed completely, causing multiple fatalities (thought to be 33). The collapsed portion fell onto an adjacent building, damaging it as well. The wing without the additional loads suffered a soft story collapse of the ground floor, but remained standing.

Damage state description

The Mansi Apartment complex suffered two damage states; one wing suffered a complete pancake collapse while the other suffered a ground story collapse and additional shear cracking. The two wings were poorly connected to one another, and this poor diaphragm continuity might have contributed to the survival of the wing left standing after the earthquake, as the poor detailing of the slabs and beams caused them to fail before pulling the other wing down.

Summary of causes of damage

1. For both wings of the building, the open ground story used for parking caused large deformation demands, and the ground floor suffered soft story effects as well as shear failures due to the absence of confining steel. 2.The insufficient design and poor construction quality meant that the building was stretched to its limit capacity before the earthquake. There was a high axial stress ratio in columns with poor residual bending capacity available for flexural bending, especially at the perimeter of the building, with cantilevers and the load of the rooftop tank and pool causing permanent bending stresses. The shaking did not cause the collapse, it was simply the catalyst for it. 3.The addition of the tank and swimming pool on the roof is both thought to HAVE and thought to HAVE NOT contributed significantly to the torsional behavior in the collapse. From EQ Spectra, Supplement A to Volume 18, "The flexible half of the building fell on an adjacent two-story building about 10m away, which seems to support a conclusion of amplified torsional behavior of the building". From the Field Report by EEFIT, "This addition (not included in the original design plans) elongated the natural period of the structure causing this portion of the structure to resonate with the long period ground motion and collapse." From Alpa Sheth, the load on the building was ~6600 tons, and the additional load from the tank and pool was about 100 tons; eccentricity due to the tank and pool was ~0.18m, so the additional structures on the roof did not significantly contribute to torsional behavior due to eccentricity between the center of rotation and the center of mass. 4. The poor diaphragm action and insufficient connection between each of the wings and the central stair/elevator core means that the two wings acted independently of one another. This poor connectivity likely saved the second wing from being brought down as the first wing collapsed completely.

Observed Design and Construction Characteristics

 

Construction Quality

MaterialsNotesContribution to Damage
Concrete Poor concrete, no testing of concrete, low strength concrete in columns, impure water used in mix, no formal mix design, volume batching instead of weight batching.
Reinforcing steel Typical for this construction

ExecutionNotesContribution to Damage
Conveyance/placement of concrete Typical for this construction
Rebar General lack of ductile detailing; no 135 degree hooks to rings, no confining steel in columns at joints (framing beam to column), inadequate vertical reinforcement.
Field variance with design documents Typical for this construction
OtherNotesContribution to Damage
Other Factors Construction Quality Columns not tied to each other, due to aesthetic reasons.

Configuration

Plan IrregularitiesNotesContribution to Damage
Torsion Load of tank and pool on roof of one wing. Building fell on adjacent building during collapse, indicating torsion.
Perimeter boundary See typical floorplan, building description. Vertical irregularity.
Diaphragm Poor diaphragm continuity between wings and shear core.
Out-of-plane offsets in lateral resisting system
Non-orthogonal systems

Vertical IrregularitiesNotesContribution to Damage
Soft story Open ground story used for parking
Weak story
Geometric variablility of lateral resisting system Central core provided unintended design lateral resisting system; gravity framing might have assisted.
In-plane discontinuity of lateral resisting system
Mass distribution 30k Liter water tank and pool on the roof of one wing of the building.
Setback
Change in stiffness

OtherNotesContribution to Damage
Other Factors Configuration

Lateral Load Resisting System‐General

StrengthNotesContribution to Damage
Overall lack of strength Poor gravity framing, absent lateral framing (Sheth and Murty, 2012).

StiffnessNotesContribution to Damage
Extreme Flexibility Poor stiffness of building due to lack of framing system (Sheth and Murty, 2012).

Load PathNotesContribution to Damage
Collectors/Struts
Anchorage of nonstructural elements
Out-of-plane capacity of walls
Diaphragm chords Poorly connected diaphragm.
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 "High axial stress ratio in columns with poor residual bending capacity esp in columns along perimeter (with cantilevers causing permanent bending stresses) and load of tank/pool" (Sheth and Murty, 2012).
Vertical load columns drift capacity
Interference of frame action by infill

BeamsNotesContribution to Damage
Strength relative to columns
Shear controlled behavior
Continuity of longitudinal reinforcing
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
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 Ahmedabad is outside the mapped location of liquefaction (Jain et al., 2002).
Pounding
Surface Rupture

OtherNotesContribution to Damage
Pile/Pier tension capacity

MiscellaneousNotesContribution to Damage
Spread footing capacity Shallow footings (Sheth and Murty, 2012).
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

Stabilization

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/products-page/reconnaissance-issues/earthquake-spectra-18-supplement-a-july-2002-bhuj-india-earthquake-of-january-26-2001-2/
Jain, S. K., Lettis, W. R., Murty, C. V. R., Bardet, J., July 2002. 2001 Bhuj, India Earthquake Reconnaissance Report.Earthquake Spectra, Volume 18, Supplement A.


http://db.concretecoalition.org/static/data/6-references/INDI002_Reference_2.pdf
Sheth, A. and Murty, C. V. R. "Concrete Coalition Project Earthquake Damage Examples from India." Earthquake Engineering Research Institute. Oakland, California. 25 June 2012.


http://ceenve3.civeng.calpoly.edu/goel/indian_eqk/eeri_abs.pdf
Goel, R. K., "Performance of buildings during the January 26, 2001 Bhuj earthquake" Abstract and Field Report Submitted to EERI.


http://ceenve3.civeng.calpoly.edu/goel/indian_eqk/index.htm#My_Photographs
Goel, R. K., 2001. "My Pictures" Civil Engineering Dpt. webpage from California Polytechnic State University. http://ceenve3.civeng.calpoly.edu/goel/indian_eqk/index.htm#My_Photographs (27 July 2012).


http://www.istructe.org/webtest/files/51/51ecb753-debf-4bcf-bcaa-b6ec9bb6ba73.pdf
Madabhushi, S. P. G. and Haigh, S. K., editors. "The Bhuj, India Earthquake of 26th January 2001, A Field Report by EEFIT" Earthquake Engineering Field Investigation Team. January 2005.


http://earthquake.usgs.gov/earthquakes/eqarchives/year/2001/2001_01_26.php
United States Geological Survey (USGS), 2012.Historic Earthquakes- Magnitude 7.7 India http://earthquake.usgs.gov/earthquakes/eqarchives/year/2001/2001_01_26.php (24 July 2012).