The structure is basically regular in plan, 5 bays of 8.26 m plus 1 bay of 7.21 m in the north-south direction, 6 bays of 8.23 m in the east-west direction. Typical story heights are 3.25 m except for the ground floor that is 3.25 m. The floor system is a...

Prepared By: Miguel Robles
Occupancy: Commercial
Year Built: 1978
Height: 32.85 m
Number of stories: 10
Stories below ground: 1
Size: 23359 sqm
Original Code:
Modification: Retrofit
Year Modified: 1979
Code of Modification:
Lateral Load System: Frames with Masonry Infill
Other Load System: Waffle flat slab
Vertical Load System: Waffle or pan-joist with columns
Other Vertical Load System:
Foundation : Piles or Piers
Other Foundation :
Country: Mexico
State: Distrito Federal
City: Mexico City
Street:
Latitude: 19.385171
Longitude: -99.154806


 

10-story office building

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 0.50g north-south direction, 0.86g east-west direction.
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

The damage consisted mainly of diagonal tension cracking in the columns. Slab flexural and diagonal tension cracking is present in all areas. The whole building settled. The largest differential settlement was about 50 cm, and the stairs and elevators shaft differential settlement was over 20 cm (Meli and Lopez, 1986).

Damage state description

The masonry walls were severely damaged, especially the stairs and elevators shaft. Almost all the columns were damaged. Columns B3, B4 and B5 were among the most severely damaged, and the most drastic failure occurred at level 6 column G1 with shear cracks in both directions and rebar buckling. Slab damages were present in all areas with some cracks going side-to-side of the stems (the worst cases occurred between axes B and C at levels 2, 3, 4 and 5). There was evidence of concrete bearing at slab/column joints (Meli and Lopez, 1986).

Summary of causes of damage

1. The building was extremely flexible due to low stiffness of the waffle slab. 2. The entire building settled and severe differential settlement towards one of the corners and at the stairs and elevators shaft indicate inadequate proportioning of the foundation. 3. Insufficient strength of the waffle flat slab resulted in generalized cracking on the entire building. 4. Shear cracking in columns might be the result of poor rebar detailing, especially the transverse reinforcement. 5. The east-west crack in the slab might have been caused by the differential settlement of the elevators shaft. (Meli and Lopez, 1986)

Observed Design and Construction Characteristics

 

Construction Quality

MaterialsNotesContribution to Damage
Concrete
Reinforcing steel

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

Configuration

Plan IrregularitiesNotesContribution to Damage
Torsion Masonry infill at the back side of the building
Perimeter boundary Re-entrant corners at axis F
Diaphragm
Out-of-plane offsets in lateral resisting system
Non-orthogonal systems

Vertical IrregularitiesNotesContribution to Damage
Soft story
Weak story
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 Waffle flat slab cracking in all areas

StiffnessNotesContribution to Damage
Extreme Flexibility Large periods

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 Poor ductile detailing, especially with transverse reinforcement

Lateral Load Resisting System‐Frames

ColumnsNotesContribution to Damage
Shear strength Shear cracks and failures
Flexural strength Small flexure/shear cracks
Axial load ratio
Vertical load columns drift capacity
Interference of frame action by infill Partial height infill walls

BeamsNotesContribution to Damage
Strength relative to columns
Shear controlled behavior Shear failures in waffle flat slab stems
Continuity of longitudinal reinforcing
Loss of vertical capacity Bearing at slab/column joints
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
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 Building settlement

MiscellaneousNotesContribution to Damage
Spread footing capacity
Other Factors Lateral Load Resisting Systems-Other-Foundations

OtherNotesContribution to Damage
Other Factors Lateral Load Resisting Systems-Other-Misc Failure of confined masonry elevator shaft

Repair and Retrofit Information

 

Type of Retrofit or Repair

Unknown

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

 

Meli, R., Lopez, C., 1986. "Evaluacion de los Efectos de los Sismos de Septiembre en la Ciudad de Mexico, Parte II, Anexo". Instituto de Ingenieria, UNAM. (Building LR10-07).


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.


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.