These buildings are three rectangular, structurally identical 2-story steel frame structures with concrete shear walls on the short ends. They are located on the site in two roughly parallel lines (See site plan for exact orientation). ...

Prepared By: Sarah Bettinger
Occupancy: Commercial
Year Built: 1960
Number of stories: 2
Stories below ground: 0
Original Code:
Modification: none
Year Modified: N/A
Code of Modification: N/A
Lateral Load System: Shear Wallrete
Other Load System:
Vertical Load System: One-way slab and beams with columns
Other Vertical Load System: Gravity system is steel framed
Foundation : Piles or Piers
Other Foundation : Likely either liquifiable soil or unknown fill
Country: United States
State: California
City: Northridge
Street: 8500 Balboa Boulevard
Latitude: 34.22
Longitude: -118.5


Harman Intl 1,2,3

Earthquake Information



Earthquake Date 34351
Moment Magnitude 6.7
Epicentral Distance 4
Local Intensity
Site Description
PGA Lateral 0.458 (g)
PGA Vertical None (g)
Ground motion recording stations LABSN Station 00003, 17645 Saticoy St., Northridge, CA
Distance to station 2.5
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

All of the buildings were damaged and lost some lateral load capacity, but were not close to collapse. The walkway that connected the buildings badly damaged and was leaning and tilted to one side.

Damage state description

Diagonal shear cracks were observed at the boundaries of some walls. Yielding and elongation fracture of longitudinal reinforcing occurred. Reinforcing bars buckled at the bases of some walls. Horizontal (sliding) shear failure planes were documented at the bases of some walls. Concrete cracked and spalled at compression zones. There was no significant diaphragm damage.

Summary of causes of damage

1. The cracking on the steel beam was caused by the inadequate ability of the beam to accommodate the deformations associated with the earthquake. 2. Diagonal cracks were due to excessing shear, but there was no observed failure. 3. Fracture of boundary reinforcing may have been due to inadequate detailing.

Observed Design and Construction Characteristics


Construction Quality

MaterialsNotesContribution to Damage
Reinforcing steel

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


Plan IrregularitiesNotesContribution to Damage
Perimeter boundary
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
Change in stiffness

OtherNotesContribution to Damage
Other Factors Configuration

Lateral Load Resisting System‐General

StrengthNotesContribution to Damage
Overall lack of strength Sliding shear failure plane at bottom of wall

StiffnessNotesContribution to Damage
Extreme Flexibility

Load PathNotesContribution to Damage
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
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

OtherNotesContribution to Damage
Other Factors Lateral Load Resisting System-Frames

Lateral Load Resisting System‐Shear Walls

ShearNotesContribution to Damage
Diagonal tension/compression Diagonal cracks due to shear, but no failure
Sliding Shear At base of wall

FlexureNotesContribution to Damage
Compression zone buckling capacity Cracking and spalling of concrete at compression zone.
Discontinuity of wall No discontinuity.
Boundary reinforcing fracture/buckling Fracture of reinforcing at boundary zone. Zones might not have been detailed.
Boundary Reinforcing at openings Unsure if there are openings in shear wall

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

Lateral Load Resisting System‐Infills

InfillsNotesContribution to Damage
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 Liquefaction zone in the area; Since the design was for piles for 2-story building, liquefaction might have been a concern. Likely did not contribute to damage, if present.
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


Hazard Level


Retrofit or Repair Code


Other Retrofit or Repair Code

Recommendations call for badly damaged walls to be rebuilt to current code. (UBC 1994)

Lateral Analysis


Other Lateral Analysis

Design Strategy

The strategy of the retrofit was to repair damage and to bring the structures up to the current code. Replacement of the damaged concrete walls was possible due to the fact that the gravity framing system was steel.

Retrofit Summary

The following recommendations were made for repair/retrofit: 1. Remove damaged walls and rebuild them to the current code (UBC 1994). 2. Walkway between buildings to be demolished and replaced. 3. Lightly damaged walls to be either left as it or repaired with epoxy injection. 4. Repair steel beam which had a fracture at the connection.

Osteraas, John, and Peter Somers, 1996. Reinforced Concrete Structures.Earthquake Spectra,11, Supplement C, Vol. 2, 5253.
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.
United States Geological Survey (USGS), 2009.CISN ShakeMap for Northridge Earthquake, (9 July 2012).
United States Geological Survey (USGS), 2009.CISN Peak Accel. (in %g) for Northridge Earthquake, (9 July 2012).
Hauksson, Egill, 1996. Seismology.Earthquake Spectra,11, Supplement C, Vol. 2, 1-12.

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