The 215 Fremont Building was built in 1927 as a warehouse but had been converted into an office building by the time the structure was damaged in the Loma Prieta earthquake. The 7-story, L-shaped structure had floor plates of roughly 46,000 sf and a smal...

Prepared By: Quinn Peck
Occupancy: Commercial
Year Built: 1927
Height: ft
Number of stories: 7
Stories below ground: 1
Size: 320,000 gsf
Original Code:
Modification: Unknown
Year Modified: 2001
Code of Modification: UBC 1997
Lateral Load System: Shear Wallrete
Other Load System:
Vertical Load System: Flat Slab with Columns
Other Vertical Load System:
Foundation : Spread Footings
Other Foundation :
Country: United States
State: California
City: San Francisco
Street: 215 Fremont Street, San Francisco, CA 94105
Latitude: 37.789
Longitude: -122.3942


 

215 Fremont St.

Earthquake Information

 

 

Earthquake Date 10/17/1989
Moment Magnitude 6.9
Epicentral Distance 95
Local Intensity VII MMI
Site Description A geotechnical investigation indicated that the building's underlying site conditions included different regions of dense, silty sands and sandy silts. These existing site conditions mean that the that differential settling and liquefaction were real possibilities.
PGA Lateral None (g)
PGA Vertical None (g)
SaT
Ground motion recording stations CGS - CSMIP Station 58480
Distance to station 0.6
Station Latitude 37.3792
Station Longitude -122.401
Ground Motion Summary The October 17, 1898 Loma Prieta earthquake occured along the San Andreas fault near the summit of Loma Prieta Mountain at a depth of approximately 18 kilometers. Geodetic and seismic network data suggest right-lateral strike-slip and reverse movement on a northwest-striking plane dipping 70 degrees to the southwest. The rupture zone had an area of roughly 300 square kilometers. The earthquake and subsequent aftershocks filled a spatial gap in observed seismicity over the previous 20 years.

 

Damage Information

 

 

Performance summary

The 215 Fremont Street building was severely damaged during the Loma Prieta earthquake and stood vacant for more than ten years before Middlebrook + Louie (now Louie International) completed a seismic renovation and expansion of the structure in 2001.

Damage state description

"Extensive damage occurred to most of the spandrels on the side of the building facing Howard Street. The cracking tended to be horizontal, except near the corners where X-cracks were formed." (Lew, 1990)

Summary of causes of damage

1. The overall lack of lateral strength resulted in significant structural damage despite the relatively low level of shaking in the area.

Observed Design and Construction Characteristics

 

Construction Quality

MaterialsNotesContribution to Damage
Concrete Relatively low strength concrete.
Reinforcing steel Inspection indicated square reinforcing bars were used.

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 The existing structure was likely not designed to withstand significant lateral loads, considering it was built in 1927.

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
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
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

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

Unknown

Other Retrofit or Repair

Performance Level

Unknown

Hazard Level

Unknown

Retrofit or Repair Code

Unknown

Other Retrofit or Repair Code

UBC 1997

Lateral Analysis

Unknown

Other Lateral Analysis

Design Strategy

After standing vacant for 10 years, a retrofit and expansion plan was carried out that brought the structure up to current code (UBC 1997) while adding two additional floors above the existing roof. The architectural design called for the removal of the existing concrete facade along the west face of the building in favor of a more attractive glass curtain wall. To accommodate both challenges, the revamped structural system was designed to utilize the full length and width of the structure to resist the seismic overturning moment thus minimizing the effect on the foundation. The original design strategy called for a diagonal strut arrangement of shear walls, but was then thrown out due to incompatibilities with the architectural plan. A similar pattern of steel braced frames was then considered and the final design utilized a hybrid of the two concepts - perimeter braced frames along the perimeter with concrete infill shear walls selectively located throughout the buildings interior. The steel frames were connected to the existing concrete columns through a "shear-block" connection and concrete infill walls were installed at various locations, including at the reentrant corner of the perimeter facade, the stairwell and the elevator core. These shear walls were connected to the existing concrete columns using horizontal dowels and the columns were utilized as part of the boundary elements. To accommodate the significant differences in stiffness between the concrete shear walls and the exterior steel braced frames, the diaphragm was strengthened in various locations using cast-in-place collector beams. The vertical addition was a steel frame structure.

Retrofit Summary

By using a hybrid structural system, the designers were able to alleviate the induced shear forces that accumulated in the existing concrete floor slabs and punched exterior walls while opening up the west elevation of the building to accommodate a new glass curtain wall. Additionally, the retrofit had to minimize the seismic overturning forces induced on the foundation by utilizing the full length and width of the building while still accommodating the architectural considerations.

References

 

http://db.concretecoalition.org/static/data/6-references/USA005_Reference_1.pdf
Lew, H. S., 1990. Performance of Structures During the Loma Prieta Earthquake of October 17, 1989.National Institute of Standards and Technology (NIST) Special Publications778.


http://www.wiley.com/WileyCDA/WileyTitle/productCd-0471700916.html
Kellogg, J. K., Filar, L., Amin, N. R., Wan, V., 2007. Renovated Office Building at 215 Fremont Street, San Francisco, California.Architectural Graphic Standards, 11th Edition,The American Institute of Architects, 5558.


http://www.concrete.org/PUBS/JOURNALS/AbstractDetails.asp?ID=12502
Amin, N. R., Figueira, D., and Wan, V., 2002. Innovative Seismic Retrofit Scheme for 215 Fremont Street Building, San Francisco, California,ACI Special Publications209, 207230.


http://eqs.eeri.org/resource/1/easpef/v6/iS1/p7_s1?isAuthorized=no
Borcherdt, R. D. and Donovan, N. C., 1990. Geosciences,Earthquake Spectra,6, Supplement, 724.


http://db.concretecoalition.org/static/data/6-references/USA004_Reference_4.pdf
Plafker, G., and J. Galloway, 1989. Lessons learned from the Loma Prieta, California earthquake of October 17, 1989. USGS Circular 1045, 48 pp.


http://db.concretecoalition.org/static/data/3-additional-ground-motion/USA004_Ground_Motion_1.jpeg
United States Geological Survey (USGS), 2009.CISN Rapid Instrumental Intensity Map for Loma Prieta Earthquake,http://earthquake.usgs.gov/earthquakes/shakemap/nc/shake/LomaPrieta/ (20 July 2012).


http://eqs.eeri.org/resource/1/easpef/v6/iS1/p25_s1?isAuthorized=no
Borcherdt, R. D. and Donovan, N. C., 1990. Ground Motion,Earthquake Spectra,6, Supplement, 2580.


Louie International, 2011.Louie International Structural Engineers. http://www.louieintl.com (26 July, 2012).


http://www.seaoc.org/bookstore/technicalpublications.html
Schmid, Ben L., 1991. Reflections on the October 17, 1989 Loma Prieta Earthquake.Ad Hoc Reconnaissance Committee of the Structural Engineers Association of California.