"The building is located in the lake bed of Mexico City. It was designed and constructed in 1959 and is used as a warehouse with an area of 1,996 square meters per floor. The structure is located at the corner of a block and consists of a basement, ground...

Prepared By: Miguel Robles
Occupancy: Industrial
Year Built: 1959
Height: 13.6 m
Number of stories: 4
Stories below ground: 1
Size: 9980 sqm
Original Code:
Modification: none
Year Modified:
Code of Modification:
Lateral Load System: MomentFrame
Other Load System:
Vertical Load System: Two-way slab and beams with columns
Other Vertical Load System:
Foundation : Mat
Other Foundation : with retaining walls around the perimeter
Country: Mexico
State: Distrito Federal
City: Mexico City
Street:
Latitude: 19.385171
Longitude: -99.154806


 

4-story warehouse

Earthquake Information

 

 

Earthquake Date 31309
Moment Magnitude 8.1
Epicentral Distance None
Local Intensity VIII MMI
Site Description "Mexico City lies in the southwestern quadrant of a broad basin which was originally formed by block faulting of an uplifted plateau. It was subsequently blocked by successive lava flows that formed a dam across the valley just south of Mexico City. This dam resulted in the formation of Lake Texcoco, which slowly began to fill with silt, clay, and ash from nearby volcanoes. This lake bed has been used for the expansion of Mexico City. Today much of the city rests on lake deposits, which overlay older sedimentary sequences" (NBS, 1987).
PGA Lateral 0.17 (g)
PGA Vertical None (g)
SaT
Ground motion recording stations SCT (Secretara de Comunicaciones y Transportes).
Distance to station None
Station Latitude 19.394
Station Longitude -99.148
Ground Motion Summary "The September 1985 Michoacn, Mexico earthquake occurred as a result of the subduction of the Cocos Plate along the Middle American Trench beneath the North American and Caribbean plates. The earthquake initiated at 18.2N, 102.6W, with a focal depth of approximately 18 km, and propagated approximately 170 km to the southeast. Because of the unrelieved accumulated strains caused by the slip movement (about 57 mm/year), the area was believed to have the potential for a major earthquake. A preliminary estimate of the seismic moment for the main shock is 0.9-1.5X10^28 dyne-cm (0.9-1.5X10^21 N-m), yielding a moment magnitude of 7.97 to 8.12 for the main shock" (NBS, 1987).

 

Damage Information

 

 

Performance summary

Most of the damage was concentrated in the second floor of the building. The elements that suffered most of the damage were the columns. No beam or slab damage was found. There was no evidence of pounding of the structure against adjacent buildings. There were no foundation failures observed (Aguilar et al., 1996).

Damage state description

Columns that developed cracks larger than 1 mm, suffered concrete spalling, and exposed, buckled and/or fractured reinforcing bars were observed. The most damaged columns in the second floor were B2 and B6. The facade on the axis 10 walls were cracked extensively. Some perimeter walls in the third and fourth floors were cracked, and in some cases failed locally. The walls around the stairways also suffered cracking. The connection between the stairway concrete ramp and the floor slabs experienced extensive cracking (Aguilar et al., 1996).

Summary of causes of damage

1. The damage on the second floor was primarily due to the restraint provided by the brick infills, which produced a short column effect. 2. Excessive bar splicing at the same location resulted in failure at that section. 3. Lack of confinement by transverse reinforcement allowed bar buckling and failure. (Aguilar et al., 1996).

Observed Design and Construction Characteristics

 

Construction Quality

MaterialsNotesContribution to Damage
Concrete
Reinforcing steel

ExecutionNotesContribution to Damage
Conveyance/placement of concrete
Rebar Excessive bar splicing at the same location, and lack of adequate confinement in columns
Field variance with design documents
OtherNotesContribution to Damage
Other Factors Construction Quality

Configuration

Plan IrregularitiesNotesContribution to Damage
Torsion
Perimeter boundary
Diaphragm
Out-of-plane offsets in lateral resisting system
Non-orthogonal systems

Vertical IrregularitiesNotesContribution to Damage
Soft story
Weak story Most of the damage was concentrated on the second floor
Geometric variablility of lateral resisting system
In-plane discontinuity of lateral resisting system
Mass distribution
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
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 Excessive bar splicing at the same location
Axial load ratio
Vertical load columns drift capacity
Interference of frame action by infill Bricks infills produced captive columns

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
Exterior
Corner

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 Extensive cracking and local failures
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
Other Factors Lateral Load Resisting Systems-Other-Foundations Building tilted 20 cm

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

Repair and Retrofit Information

 

 

Type of Retrofit or Repair

Improved Performance

Other Retrofit or Repair

Performance Level

Unknown

Hazard Level

Unknown

Retrofit or Repair Code

Other

Other Retrofit or Repair Code

1976 Federal District Code and Emergency Norms

Lateral Analysis

Equivalent lateral force

Other Lateral Analysis

Design Strategy

Increase the strength and stiffness of the structure by encasing both beams and columns in reinforced concrete. This alternative did not change the load pattern (as would have happened using shear walls) and there was no need to strengthen the foundations (Jara et al., 1989). The material properties for the repair and strengthening of the structure are: - Concrete strength: f 'c = 250 kg/cm2 - Reinforcing steel: fy = 4,200 kg/cm2 - Plain #2 steel bars: fy = 2,530 kg/cm2 (Aguilar et al., 1996)

Retrofit Summary

All beams and columns were encased in reinforced concrete with a minimum jacket of 12 cm, concrete surfaces were roughened to enhance the stress transfer, and floors were shored during the repairs without being restored to original elevations. Damaged columns were repaired by substituting buckled/fractured bars with new welded steel bars, and the longitudinal reinforcement was made continuous using holes drilled in the slab and anchored to the foundations. The longitudinal reinforcement in beams was made continuous by passing the bars around the columns, and the transverse reinforcement was passed through holes drilled in the slab. The masonry and brick walls were separated from the frames, the damaged brick wall partitions were replaced, and the stairway ramp was replaced (Aguilar et al., 1996).

References

 

http://db.concretecoalition.org/static/data/6-references/MEXI006_Reference_01.pdf
Aguilar, J. et al., 1996. "Rehabilitation of Existing Reinforced Concrete Buildings in Mexico City. Case Studies". Ferguson Structural Engineering Laboratory, The University of Texas at Austin, August 1996. (Building A)


http://earthquakespectra.org/doi/abs/10.1193/1.1585518
M. Jara, C. Hernandez, R. Garcia, and F. Robles (1989). "The Mexico Earthquake of September 19, 1985Typical Cases of Repair and Strengthening of Concrete Buildings". Earthquake Spectra: February 1989, Vol. 5, No. 1, pp. 175-193.


http://www.nist.gov/manuscript-publication-search.cfm?pub_id=908821
National Bureau of Standards (NBS), 1987. "Engineering Aspects of the September 19, 1985 Mexico Earthquake". NBS Building Science Series 165.


http://earthquake.usgs.gov/earthquakes/shakemap/atlas/shake/198509191317/
United States Geological Survey (USGS), 2008. "USGS ShakeMap: Michoacan, Mexico". ShakeMap Atlas, 2012.


"Mexico". 18.41 N and 102.37 W. Google Earth/USGS, 2012.