Cart
0
Product
Products
(empty)
No products
To be determined
Shipping
$0.00
Total
Product successfully added to your shopping cart
Quantity
Total
There are 0 items in your cart.
There is 1 item in your cart.
Total products
Total shipping
To be determined
Total
Sale!
View larger
View larger
ACI SP-187
New product
ACI SP-187 1999 Edition, January 1, 1999 Seismic Response of Concrete Bridges
More info
Description / Abstract:
INTRODUCTION
Prior to the 1933 Long Beach earthquake there was no special consideration for seismic design of buildings or bridges in California. The severe damage to schools that resulted from that seismic event resulted in creation of the Structural Engineer license and a requirement for speciaI consideration of seismic forces in the design of public schools in California. After the 1940 EI Centro earthquake the bridge design office of the California Division of Highways developed minimal seismic design factors for bridges. The 1940 El Centro record was digitized and used as the seismic design spectra for over 30 years before an earthquake of greater magnitude occurred in California. The 1971 San Fernando earthquake caused severe damage to hospitals, public utilities, and freeway bridges, recording a peak ground acceleration of 1.Og and large ground displacements. This earthquake caused both building and bridge designers to revise their design criteria and structural details to provide better resistance to the forces and displacements of major seismic events. The American Association of State Highway and Transportation Officials (AASHTO) is the agency responsible for development of bridge design specifications for nationwide use. AASHTO has typically adopted seismic design criteria modeled after those developed in California, and the initial adoption is only as a guide specification. Until the 1989 Lorna Prieta earthquake most other states in the United States had not been concerned with seismic design for bridges, considering it a California or West Coast problem. For example, the 1940 California seismic design specifications were not adopted by AASHTO until 1961, and the 1973 California seismic design specifications were not adopted nationally until 1983. In May, 1990, responding to the disastrous 1989 Loma Prieta earthquake in California, AASHTO finally adopted the 1983 "Guide Specifications For Seismic Design of Highway Bridges" as a mandatory requirement for those states which have a seismic hazard. Interestingly, some 37 states in the US have some level of seismic hazard. Understandably, there are hundreds of bridges in these other states which have been designed to seismic criteria that are not adequate for seismic forces and displacements that we know today. The seismic retrofit details designed by the California bridge engineers can be of great benefit to those states who are faced with seismic threats of lesser magnitude, and with little financial support for seismic retrofitting, and much less for research and seismic detail development.
The California State Department of Transportation (Caltrans) owns and maintains over 12,000 bridges (spans over 20 feet). There are an equal number on the City and County system. The bridge office maintains the condition data for all these and some 6,000 other highway structures such as culverts (spans under 20 feet), pumping plants, tunnels, tubes, Highway Patrol inspection facilities, maintenance stations, toll plazas and other transportation related structures. Structural details and the current condition data are maintained in the department's bridge maintenance files as part of the National Bridge Inventory System (NJ3IS) required by the US Congress and administered by the Federal Highway Administration (FHWA). This data is updated and submitted annually to the FHWA and is the basis upon which some of the Federal gas tax funds are allocated and returned to the states. The maintenance, rehabilitation and replacement needs for bridges are prorated against the total national needs. Seismic retrofit strengthening is eligible for use of those funds.
The two most significant earthquakes in California in recent history that produced the best information for bridge designers were the 1989 Loma Prieta and the 1994 Northridge events. While the experts consider these to be only moderate earthquakes, it is important to note the good performance of the many bridges that had been designed for the improved seismic criteria or retrofitted with the early era seismic retrofit details. This reasonable performance of properly designed newer and retrofitted older bridges in a moderate earthquake is significant for the rest of the United States because that knowledge can assist engineers in designing new bridges and in designing an appropriate seismic retrofit program for their older structures. Although there is a necessary concern for the "Big One" in California, especially for the performance of important structures, it must be noted that many structures which vehicle traffic can bypass need not be designed or retrofitted to the highest standards. It is also important to note that there will be many moderate earthquakes that will not produce the damage associated with a maximum event. These are the earthquake levels that should be addressed first in a multi phased retrofit strengthening program, given the limited resources that are available. Cost benefit analysis of retrofit details is essential to measure and insure the effectiveness of a program. It has been the California experience that a great deal of insurance against collapse can be achieved for a reasonable cost, typically ten percent of replacement cost for normal highway bridges. It is also obvious that designing for a performance criteria that provides full service immediately after a major earthquake may not be economically feasible. The expected condition of the bridge approach roadways after a major seismic event must be evaluated before large investments are made in seismic retrofitting the bridges to a full service criteria. There is little value to the infrastructure in investing large sums to retrofit a bridge if the approaches are not functioning after a seismic event. Roadways in the soft muds around most harbors and rivers are potentially liquefiable and will require repair before the bridges can be used.
Approximately 2,200 of California's 12,000 bridges are located in the Los Angeles area so it is significant to examine the damage and performance of bridges in the Northridge earthquake of January 17, 1994. About 1,200 of these bridges were in an area that experienced ground accelerations greater than 0.25g and several hundred were in the area that experienced ground accelerations of 0.50g or greater. There were 132 bridges in this area with post San Fernando retrofit details completed (Hinge and Joint restrainer cables) and 63 with post Loma Prieta retrofit details completed (Additional joint restrainers and column strengthening). Ail of these retrofitted bridges performed extremely well (not closed to public traffic) and most of the other bridges performed well during the earthquake; newer bridges designed and constructed to Caltrans' current seismic specifications survived the earthquake with very little damage. Seven older bridges, designed for a smallerearthquake force or without the ductility of caltrans' current design, sustained severe damage during the earthquake. Another 230 bridges suffered some damage ranging from serious problems of column and hinge damage to cracks, bearing damage and approach settlements, but these bridges were not closed to traffic during repairs.
Prior to the 1933 Long Beach earthquake there was no special consideration for seismic design of buildings or bridges in California. The severe damage to schools that resulted from that seismic event resulted in creation of the Structural Engineer license and a requirement for speciaI consideration of seismic forces in the design of public schools in California. After the 1940 EI Centro earthquake the bridge design office of the California Division of Highways developed minimal seismic design factors for bridges. The 1940 El Centro record was digitized and used as the seismic design spectra for over 30 years before an earthquake of greater magnitude occurred in California. The 1971 San Fernando earthquake caused severe damage to hospitals, public utilities, and freeway bridges, recording a peak ground acceleration of 1.Og and large ground displacements. This earthquake caused both building and bridge designers to revise their design criteria and structural details to provide better resistance to the forces and displacements of major seismic events. The American Association of State Highway and Transportation Officials (AASHTO) is the agency responsible for development of bridge design specifications for nationwide use. AASHTO has typically adopted seismic design criteria modeled after those developed in California, and the initial adoption is only as a guide specification. Until the 1989 Lorna Prieta earthquake most other states in the United States had not been concerned with seismic design for bridges, considering it a California or West Coast problem. For example, the 1940 California seismic design specifications were not adopted by AASHTO until 1961, and the 1973 California seismic design specifications were not adopted nationally until 1983. In May, 1990, responding to the disastrous 1989 Loma Prieta earthquake in California, AASHTO finally adopted the 1983 "Guide Specifications For Seismic Design of Highway Bridges" as a mandatory requirement for those states which have a seismic hazard. Interestingly, some 37 states in the US have some level of seismic hazard. Understandably, there are hundreds of bridges in these other states which have been designed to seismic criteria that are not adequate for seismic forces and displacements that we know today. The seismic retrofit details designed by the California bridge engineers can be of great benefit to those states who are faced with seismic threats of lesser magnitude, and with little financial support for seismic retrofitting, and much less for research and seismic detail development.
The California State Department of Transportation (Caltrans) owns and maintains over 12,000 bridges (spans over 20 feet). There are an equal number on the City and County system. The bridge office maintains the condition data for all these and some 6,000 other highway structures such as culverts (spans under 20 feet), pumping plants, tunnels, tubes, Highway Patrol inspection facilities, maintenance stations, toll plazas and other transportation related structures. Structural details and the current condition data are maintained in the department's bridge maintenance files as part of the National Bridge Inventory System (NJ3IS) required by the US Congress and administered by the Federal Highway Administration (FHWA). This data is updated and submitted annually to the FHWA and is the basis upon which some of the Federal gas tax funds are allocated and returned to the states. The maintenance, rehabilitation and replacement needs for bridges are prorated against the total national needs. Seismic retrofit strengthening is eligible for use of those funds.
The two most significant earthquakes in California in recent history that produced the best information for bridge designers were the 1989 Loma Prieta and the 1994 Northridge events. While the experts consider these to be only moderate earthquakes, it is important to note the good performance of the many bridges that had been designed for the improved seismic criteria or retrofitted with the early era seismic retrofit details. This reasonable performance of properly designed newer and retrofitted older bridges in a moderate earthquake is significant for the rest of the United States because that knowledge can assist engineers in designing new bridges and in designing an appropriate seismic retrofit program for their older structures. Although there is a necessary concern for the "Big One" in California, especially for the performance of important structures, it must be noted that many structures which vehicle traffic can bypass need not be designed or retrofitted to the highest standards. It is also important to note that there will be many moderate earthquakes that will not produce the damage associated with a maximum event. These are the earthquake levels that should be addressed first in a multi phased retrofit strengthening program, given the limited resources that are available. Cost benefit analysis of retrofit details is essential to measure and insure the effectiveness of a program. It has been the California experience that a great deal of insurance against collapse can be achieved for a reasonable cost, typically ten percent of replacement cost for normal highway bridges. It is also obvious that designing for a performance criteria that provides full service immediately after a major earthquake may not be economically feasible. The expected condition of the bridge approach roadways after a major seismic event must be evaluated before large investments are made in seismic retrofitting the bridges to a full service criteria. There is little value to the infrastructure in investing large sums to retrofit a bridge if the approaches are not functioning after a seismic event. Roadways in the soft muds around most harbors and rivers are potentially liquefiable and will require repair before the bridges can be used.
Approximately 2,200 of California's 12,000 bridges are located in the Los Angeles area so it is significant to examine the damage and performance of bridges in the Northridge earthquake of January 17, 1994. About 1,200 of these bridges were in an area that experienced ground accelerations greater than 0.25g and several hundred were in the area that experienced ground accelerations of 0.50g or greater. There were 132 bridges in this area with post San Fernando retrofit details completed (Hinge and Joint restrainer cables) and 63 with post Loma Prieta retrofit details completed (Additional joint restrainers and column strengthening). Ail of these retrofitted bridges performed extremely well (not closed to public traffic) and most of the other bridges performed well during the earthquake; newer bridges designed and constructed to Caltrans' current seismic specifications survived the earthquake with very little damage. Seven older bridges, designed for a smallerearthquake force or without the ductility of caltrans' current design, sustained severe damage during the earthquake. Another 230 bridges suffered some damage ranging from serious problems of column and hinge damage to cracks, bearing damage and approach settlements, but these bridges were not closed to traffic during repairs.