The Administration Building at the California State University in Northridge was a concrete shear wall building. The majority of the shear walls were discontinuous (vertically offset) at the second floor. The discontinuous walls were supported with column...

Prepared By: Sarah Bettinger
Occupancy: Education
Year Built: 1962
Height:
Number of stories: 5
Stories below ground: unknown
Size:
Original Code:
Modification: none
Year Modified: N/A
Code of Modification: N/A
Lateral Load System: Shear Wallrete
Other Load System:
Vertical Load System: Waffle or pan-joist with columns
Other Vertical Load System:
Foundation : Piles or Piers
Other Foundation :
Country: United States
State: California
City: Northridge
Street: 18111 Nordhoff St., Northridge, Ca. 91330
Latitude: 34.2
Longitude: -118.53


 

Cal State Northridge

Earthquake Information

 

 

Earthquake Date 34351
Moment Magnitude 6.7
Epicentral Distance 3
Local Intensity
Site Description
PGA Lateral 0.458 (g)
PGA Vertical None (g)
SaT
Ground motion recording stations LABSN Station 00003, 17645 Saticoy St., Northridge, CA
Distance to station 3.5
Station Latitude 34.2
Station Longitude -118.517
Ground Motion Summary The earthquake occurred along the Pico thrust fault, a previously undiscovered Northridge blind thrust fault, and produced some of the strongest ground motions ever recorded in North America. The earthquake started at the down-dip, southeastern corner of the Pico fault plane and ruptured up northwest approximately 15 km, with no evidence of slip above 7 km below the earth's surface. The hypocenter is believed to lie at a depth of about 19 km km at a location of 34.213, -118.537. An overall maximum horizontal ground acceleration of 1.93g was recorded at Tarzana, about 11.2 km from the epicenter.

 

Damage Information

 

 

Performance summary

In general, there was moderate damage to structural components. There was moderate damage to nonstructural components (including drop ceilings and architectural finishes).

Damage state description

Widespread cracking of concrete was observed. There was little damage to the columns that support the discontinuous walls. There was damage to the spandrel link beams between the shear walls. There were signs of lateral sliding near construction joints, including in the stairwells. There was significant slab cracking between the vertical offsets. There was shear and flexural damage at the east wall.

Summary of causes of damage

1. There was little damage to the columns that support the discontinuous walls. 2. There was damage to the spandrel link beams between the shear walls. 3. There were signs of lateral sliding near construction joints, including in the stairwells. 4. There was significant slab cracking between the vertical offsets. 5. There was shear and flexural damage at the east wall.

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
Perimeter boundary
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

StiffnessNotesContribution to Damage
Extreme Flexibility

Load PathNotesContribution to Damage
Collectors/Struts
Anchorage of nonstructural elements Moderate nonstructural damage
Out-of-plane capacity of walls
Diaphragm chords
Diaphragm openings

OtherNotesContribution to Damage
Other Factors Lateral Load Resisting System-General Damage to spandrel link beams between shear walls

Lateral Load Resisting System‐Frames

ColumnsNotesContribution to Damage
Shear strength
Flexural strength
Axial load ratio
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
Exterior
Corner

OtherNotesContribution to Damage
Other Factors Lateral Load Resisting System-Frames

Lateral Load Resisting System‐Shear Walls

ShearNotesContribution to Damage
Diagonal tension/compression Series of minor diagonal shear cracks
Sliding Shear Signs of lateral sliding near construction joints
Flexure/shear Shear and flexural damage at the east wall

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

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

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

Unknown

Other Retrofit or Repair Code

Recommendations call for building to be brought to current code. (1995)

Lateral Analysis

Unknown

Other Lateral Analysis

Design Strategy

Retrofit Summary

References

 

http://eqs.eeri.org/resource/1/easpef/v12/iS1/p49_s1?isAuthorized=no
Osteraas, John, and Peter Somers, 1996. Reinforced Concrete Structures.Earthquake Spectra,11, Supplement C, Vol. 2, 5253.


http://db.concretecoalition.org/static/data/6-references/USA001_Reference_2.pdf
Earthquake Engineering Field Investigation Team (EEFIT), 1994. The Northridge, California Earthquake of 17 January 1994: A Field Report by EEFIT. EEFIT, Institute of Structural Engineers.


http://db.concretecoalition.org/static/data/3-additional-ground-motion/USA001_Ground_Motion_1.jpg
United States Geological Survey (USGS), 2009.CISN ShakeMap for Northridge Earthquake,http://earthquake.usgs.gov/earthquakes/shakemap/sc/shake/Northridge/ (9 July 2012).


http://db.concretecoalition.org/static/data/3-additional-ground-motion/USA003_Ground_Motion_2.jpg
United States Geological Survey (USGS), 2009.CISN Peak Accel. (in %g) for Northridge Earthquake,http://earthquake.usgs.gov/earthquakes/shakemap/sc/shake/Northridge/#Peak_Ground_Acceleration (9 July 2012).


http://eqs.eeri.org/resource/1/easpef/v11/iS2/p1_s1
Hauksson, Egill, 1996. Seismology.Earthquake Spectra,11, Supplement C, Vol. 2, 1-12.


Nabih Youssef Associates. Interview, professional expertise, photos, drawings. August 17, 2012.