National Information Service for Earthquake Engineering
University of California, Berkeley
Abridged from Earthquake Spectra,
Vol 11, Supplement C, Chapter 6,
Used by permission of EERI
Immediately following the earthquake, Caltrans took measures to reopen obstructed freeway and surface street arteries as soon as possible. Removal of collapsed and/or seriously damaged structures began within one day of the earthquake. Caltrans also quickly decided to rebuild the defunct structures in their former locations with only minor adjustments to their alignments. Design, review, and construction of the replacement structures was expedited. The entire road network was planned to be fully restored by 1 December 1994. New design criteria were evolved for the design of the replacement structures with the assistance of an independent seismic safety review panel convened for the reconstruction. Ten replacement bridges were designed to replace five that had collapsed and five that were damaged. A summary of the replacement bridges is provided in Table 3. Replacement costs are 1994 projections. One bridge, the Truck Connector Overcrossing (Bridge #53-1962F), was repaired, although it was intended initially to be replaced.
|Replacement Bridge||Name||Route||Replacement Cost||Date opened|
|53-1797||Gavin Canyon UC||I-5||$23,627,000||17 May 1994|
|53-387||Butte Canyon Bridge||I-5||6,765,000||18 may 1994|
|53-1609S||La Cienega-Venice Sep.||I-10||4,023,000||11 April 1994|
|53-1609 to 53-1580||La Cienega-Venice to Fairfax-Washington||I-10||34,584,000||11 April 1994|
|53-2797F||South Connector OC||I-5/SR14||8,100,000||4 Nov 1994|
|53-2798F||North Connector OC||I-5/SR14||6,500,000||4 Nov 1994|
|53-2979F and 53-2979G||Separation and Overhead Structures F and G||I-5/SR-14||24,403,000||8 July 1994|
|53-2205 R/L||Mission-Gothic UC*||East SR 118||15,433,000||13 May 1994|
|53-2206 R/L||Bull Creek Canyon Channel UC||West SR118||10,757,000||20 Nov 1994|
The design objectives adopted by Caltrans for the Northridge earthquake replacement structures were intended to prevent collapse under a maximum credible earthquake without explicitly addressing damageability and functionality issues for earthquakes of various magnitudes. In addition, the designs adopted the current Caltrans approach that aims to force inelastic action at predetermined and well-detailed locations in columns while the remainder of the structure remains essentially elastic.
Additional design measures were promulgated for the Northridge replacement structures in response to undesirable behavior observed in this and other recent seismic events. Ductile structures with a high degree of serviceability are expected to result from application of current Caltrans seismic design approaches supplemented by the additional measures described below.
Meeting the above design objectives required a significant change and advance from current Caltrans seismic design practice.
Design constraints, besides those caused by the short timetable necessary to expedite construction, consisted of:
To facilitate the short timetable, cast-in-drilled-hole piles were used where possible and standard Caltrans multicell posttensioned box girders were used in bridge superstructures, except where steel alternates were designed.
Construction of the replacement bridge projects proceeded at a rapid pace. Six bridges and two structures of the ten replacement bridge projects were completed and opened to traffic less than six months after the earthquake. The remaining replacement bridge projects were scheduled to open before 1 December 1994. The rapid construction of the Northridge replacement bridges is facilitated by financial incentives for the contractor for early route reopening (and disincentives for late reopening) with respect to the contracted period.
Several important observations can be made regarding the performance of the transportation system. Many of these may be useful in planning future work on that system:
Astaneh, A., B. Bolt, K. M. McMullin, R. R. Donikian, D. Modjtahedi, and S.-W. Cho. 1994. Seismic performance of steel bridges during the 1994 Northridge earthquake. University of California, Berkeley. Report No. UCB/CE-STEEL-94/01. April.
Brodsly, D. 1981. L. A. Freeway. Berkeley: University of California Press.
Buckle, I.G.ed. 1994. The Northridge, California earthquake of January 17, 1994: Performance of highway bridges. NCEER-94-0008. National Center for Engineering Research, State University of New York at Buffalo, 24 March.
California Department of Transportation. 1976. Report concerning earthquake resistant design advances for state highway and bridge construction. Third Biennial Report. State of California, Business and Transportation Agency, October.
Housner, G. W. 1990. Competing against time. The Governor's Board of Inquiry on the 1989 Loma Prieta Earthquake. G. W. Housner, Chairman, State of California, Office of Planning and Research, 31 May.
Jennings, Paul C. ed. 1971. Engineering features of the San Fernando earthquake of February 9, 1971. California Institute of Technology. Report EERL 71-02, June.
Los Angeles Times. 1994. February 16.
Moehle, J. P. ed. 1994. Preliminary report on the seismological and engineering aspects of the January 17, 1994, Northridge earthquake. UCB/EERC94/01. Earthquake Engineering Research Center, January.
Priestley, M. J. N., F. Seible, and C. M. Uang. 1994. The Northridge earthquake of January 17, 1994: Damage and analysis of selected freeway bridges. University of California, San Diego. Structural Systems Research Project Report No. SSRP 94/06, February.
Priestley, M. J. N., F. Seible, R. Verma, and Y. Xiao. 1993. Seismic shear strength of reinforced concrete columns. University of California, San Diego. Structural Systems Research Project, Report No. SSRP-93/06, July.
Quon, F. 1994. Personal communication, Caltrans District 7, August 17.
Roberts, J. E. 1992. Bridge seismic and other research needs: Caltrans overview. In Proceedings, Third NSF Workshop on Bridge Engineering Research in Progress. La Jolla, California, 16 and 17 November.
Selna, L. G., L. J. Malvar, and R. J. Zelinski. 1989. Bridge retrofit testing: Hinge cable restrainers. ASCE journal of Structural Engineering 1 14 (4): 920-934.
|Part 1: Introduction and Overview||Part 2: Detailed Damage Descriptions||Part 3: Bridge Reconstruction and Conclusions|
Updated December 17, 1997.
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