San Francisco-Oakland Bay Bridge Research Articles

Eight Mile Crossing: The San Francisco-Oakland Bay Bridge

The San Francisco-Oakland Bay Bridge was the product of a team of talented contributors, each bringing expertise to bear on what would become one of the most extraordinary achievements of 20th century bridge engineering.

Traffic Impacts of Variable Pricing on the San Francisco–Oakland Bay Bridge, California

The raising of bridge tolls in the peak period on the San Francisco-Oakland Bay Bridge in California in mid-2010 provides a rare opportunity to assess traffic impacts. Carpoolers who previously traveled for free during peak hours were charged an electronic toll under this variable pricing scheme. On the basis of 29 months of time series data, the introduction of carpool charges had a stronger impact on traffic volumes than did peak period pricing of regular traffic. The estimated short-term elasticity of about −0.30 suggests significant numbers of peak hour carpoolers did not travel, switched routes, shifted to public transit, or opted to drive alone. More than half the loss in carpool traffic was estimated to be attributable to the toll increase, a far stronger influence than factors such as rising gasoline prices and unemployment. The estimated elasticity of regular traffic in response to variable pricing was −0.23, an indication that peak period motorists were fairly insensitive to pricing and a reflection of the nondiscretionary nature of many peak hour journeys. It will be important to track trends over time to gain insights into the longer term sensitivity of motorists to variable pricing on natural corridors such as the San Francisco–Oakland Bay Bridge.

Acoustic Emission Method for Real-Time Detection of Steel Fatigue Crack in Eyebar

After the discovery of a significant crack in an eyebar (fracture-critical element) on the San Francisco–Oakland Bay Bridge in California, the California Department of Transportation (Caltrans) explored possible remote monitor solutions to provide the greatest possible safeguards for the some 200,000 vehicles that used the bridge daily. Caltrans selected an acoustic emission (AE) monitoring system that allowed the detection and localization of crack initiation and growth in real time. The AE method relies on the propagation of elastic waves released by a sudden stress–strain change at the crack tip. The challenge of the AE method in a field application is the disturbance of the data by extraneous noise sources. A robust damage detection algorithm is required to differentiate relevant damage data from secondary noise sources, such as friction. Caltrans required that the proposed monitoring solution be validated through laboratory testing. This paper presents the full-scale laboratory testing of two eyebars loaded under constant amplitude fatigue to detect and locate crack growth under intense friction-type noise sources with use of the AE method. Verification is presented of AE results with ultrasonics testing, dye penetrant, and visual methods to detect damage. Linear location accuracy with simulated signal sources is discussed. The pattern recognition algorithm to differentiate noise signals and crack growth signals is presented. On the basis of this study, the AE method will be used to continuously monitor 384 eyebars with 640 AE sensors on the San Francisco–Oakland Bay Bridge.

Impact of Peak and Off-Peak Tolls on Traffic in San Francisco–Oakland Bay Bridge Corridor in California

The San Francisco–Oakland Bay Bridge is located in the heart of the San Francisco Bay Area in California and connects two of the largest cities in northern California over San Francisco Bay. In July 2010, the Bay Area Toll Authority (BATA) increased tolls on the San Francisco–Oakland Bay Bridge from a flat toll collected westbound only to weekday peak and off-peak tolls. BATA also instituted a carpool toll of $2.50 (previously carpools crossed for free) payable by FasTrak electronic toll collection tag only. With floating-car data provided by BATA, the change in travel time for the I-80, I-580, and I-880 approaches was computed by payment type (cash, FasTrak, and high-occupancy vehicle access lanes) and hour. Travel times were found to have been reduced by 0 to 16 min for cash customers (varying by time of day and approach), with varying results for FasTrak customers and little change for high-occupancy vehicle customers. Data collected by BATA at the toll plaza were analyzed by hour and payment type. The analysis found that the number of vehicles in the carpool lanes was reduced by more than 20% at times, whereas FasTrak volumes remained steady or increased and cash volumes were slightly lower than before the toll switch.

Congestion Pricing Study of San Francisco–Oakland Bay Bridge in California

The San Francisco–Oakland Bay Bridge in California is one of the most heavily traveled corridors in the United States. A study on congestion pricing was performed to address traffic congestion in this corridor. Existing toll plaza counts and travel time data were used in the estimation of traffic demand by applying queuing analysis. Regression analysis was conducted to estimate the number of drivers who would shift to other modes in response to the congestion pricing. Five congestion pricing alternatives were examined. The bigger the price differential between peak and nonpeak toll, the more delays, queue length, and duration of congestion were reduced. Of the five alternatives, the one with a $2.00 price differential between peak and nonpeak toll was selected and implemented on July 1, 2010. This adopted congestion pricing strategy was to reduce the traffic demand by 4.2% and 5.0% in the a.m. and p.m. peak periods, respectively. The congestion pricing was to reduce significant delays (24% to 30%) by removing only a fraction of the vehicles (4.2% to 5.0%) from the congested Bay Bridge. A preliminary analysis comparing traffic counts between July and September 2009 and July and September 2010 found that, in July, traffic volume decreased by 8.4% and 7.3% during the a.m. and p.m. peak periods, respectively. In September, traffic volume decreased by 6.0% and 3.9% during the a.m. and p.m. peak periods, respectively. A comprehensive evaluation study is under way to identify changes due to congestion pricing and changes due to a multitude of exogenous factors.

FUSING INCIDENT MANAGEMENT/RESPONSE WITH INFRASTRUCTURE PROTECTION/SECURITY … … THE “3 R+” CONCEPT

ABSTRACT The terrorist attacks of 9/11 brought an urgent, necessary call to protect the safety and security of the nations Critical Infrastructure/Key Resources (CI/KR). Most of these efforts have been to deter/prevent a terrorist attack through vulnerability assessment and increased physical security (e.g. “gates, guns and guards”). Just as the federal government was getting on solid ground with increased homeland security against the terrorist threat, the devastation of the 2005 Hurricanes Katrina and Rita brought to light the need for a true “All Hazards” approach to response. Added to this is the growing awareness that environmental incidents could significantly impact regional stability, and even threaten national security. Simply stated: “Yesterday'S major oil spill could be tomorrow'S national security incident.” The November 2007 allision (and resulting serious oil spill) of the tank ship COSCO BUSAN with the San Francisco-Oakland Bay Bridge, provided a glimpse into these concerns and brought increased attention back upon this long standing marine safety mission. Ironically the 2006 “Safe Seas” exercise tested almost the very scenario of the COSCO BUSAN one year ago to the day of the spill. “Safe Seas” and other major drills (like “TOPOFF,” etc.) are tremendous tools for government and private sector stakeholders to enhance preparedness to response and test existing security and infrastructure protection systems. Given the above, traditional Oil Spill Response (OSR) is now part of a broader, more complicated systems-approach to domestic Incident Management (IM). The United States Coast Guard'S Marine Environmental Protection (MEP) mission has required the unique military I regulatory service to forge a collaborative relationship with the oil and gas industry - or “sector” (as defined in the National Infrastructure Protection Plan NIPP). This government-to-industry partnership was born out of decades of marine safety prevention/response efforts most visible following the Oil Pollution Act of 1990 (OPA 90). Many involved in the field of emergency management; as well as their security counterparts recognize it is difficult to understand both IM and IP, despite the myriad of new and developing federal plans and doctrine as we pass the half way point of the first decade in the Post 9/11 “new normalcy.” Due to dynamic and synergistic partnership between the U.S. Coast Guard and the American Petroleum Institute (API) a coordination and communication opportunity was identified that resulted in a concept of simplifying the landscape via a” 3 R+” concept. The focus areas of this paper are:To bring increased clarity to the current and emerging state of interoperability between the government and the private industry sector.Provide a simplified “Big Picture” view of what private sector professionals (middle to upper management in the emergency response/safety & health fields) need to know regarding the framework of the national system for our critical infrastructure and first line response, using the oil & gas sector as an example; Note: Although the target audience for this papen/presentation are private sector professionals, primarily in the response and security fields, the plans highlighted and information outlined could apply to those working IM or IP in any industry or government sector.

Influence of Dampers on Seismic Response of Cable-Supported Bridge Towers

Nonlinear time history analyses were performed to investigate the seismic response of the new San Francisco–Oakland Bay Bridge East Span self-anchored suspension (SAS) bridge and cable-stayed (CS) bridge alternative with the signature towers protected by friction dampers and viscous dampers in lieu of the as-designed steel shear links. Response of the damper and shear link equipped towers were compared to determine if equipping bridge signature towers with passive dampers, that would not experience residual deformations, is a viable option for cable supported bridges, particularly in retrofit applications. Viscous dampers were the most beneficial to the SAS and CS tower response in the transverse direction of the bridges. Dampers placed in toggle-braced configurations further improved the tower response for the SAS bridge transverse direction by magnifying the damper displacement demands. With the addition of stiffness to the signature tower being more critical in the longitudinal direction than in the transverse direction, the diagonal friction dampers were the most beneficial in the longitudinal direction of the SAS bridge tower.

Dose–effect relationships between manganese exposure and neurological, neuropsychological and pulmonary function in confined space bridge welders

Background: Although adverse neuropsychological and neurological health effects are well known among workers with high manganese (Mn) exposures in mining, ore-processing and ferroalloy production, the risks among welders with lower...

Experimental Evaluation of Compressive Behavior of Orthotropic Steel Plates for the New San Francisco–Oakland Bay Bridge

Compression tests were conducted on two reduced-scale orthotropic plates to verify the design strength of steel box girders for the new San Francisco-Oakland Bay Bridge. The first specimen was composed of three longitudinal closed ribs and a top deck plate. It failed in global buckling, followed by local buckling in the deck plate and ribs. The second specimen, which was composed of four longitudinal T-shaped ribs and a bottom deck plate, experienced global buckling as well as local buckling in the ribs and the deck plate. The ultimate strength and failure mode of both specimens were evaluated by two bridge design specifications: the 1998 AASHTO load and resistance factor design specification and the 2002 Japanese JRA specification. Findings from code comparisons showed that: 1 Sufficient flexural rigidity of ribs were provided for both specimens; 2 the JRA specification slightly overestimated the ultimate strength of both specimens; and 3 neither specifications predicted the observed buckling sequence in Specimen 2. A general-purpose nonlinear finite element analysis program ABAQUS was used to perform correlation study. The analysis showed that the ultimate strength and postbuckling behavior of the specimens could be reliably predicted when both the effects of residual stresses and initial geometric imperfections were considered in the model.

Structural Testing of New East Bay Skyway Piers

This paper discusses 2 proof-of-concept tests conducted at 1/4 scale on a typical hollow, rectangular, reinforced concrete pier designed to support the new East Bay Skyway Structures of the San Francisco-Oakland Bay Bridge. The test units were loaded according to quasi-static, fully-reversed, cyclic loading histories to simulate the force-displacement response of the prototype pier under seismic forces. Both tests withstood inelastic deformations greater than those expected in response to the 1500-year governing design earthquake for the Bridge. Based on results from both tests, structural details such as the architectural concrete and transverse reinforcement were improved to enhance constructibility and service-level performance. This paper discusses 3 different approaches to evaluating experimental plastic hinge lengths and demonstrates the ambiguity inherent in evaluating the force-displacement behavior of such piers according to strain-based seismic performance criteria.

Issues in neurological risk assessment for occupational exposures: The Bay Bridge welders

The goal of occupational risk assessment is often to estimate excess lifetime risk for some disabling or fatal health outcome in relation to a fixed workplace exposure lasting a working lifetime. For sub-chronic or sub-clinical health effects measured as continuous variables, the benchmark dose method can be applied, but poses issues in defining impairment and in specifying acceptable levels of excess risk. Such risks may also exhibit a dose–rate effect and partial reversibility such that effects depend on how the dose is distributed over time. Neurological deficits as measured by a variety of increasingly sensitive neurobehavioral tests represent one such outcome, and the development of a parkinsonian syndrome among welders exposed to manganese fume presents a specific instance. Welders employed in the construction of piers for a new San Francisco–Oakland Bay Bridge in San Francisco were previously evaluated using a broad spectrum of tests. Results for four of those tests (Rey–Osterrieth Complex Figure Test, Working Memory Index, Stroop Color Word Test and Auditory Consonant Trigrams Test) were used in the benchmark dose procedure. Across the four outcomes analyzed, benchmark dose estimates were generally within a factor of 2.0, and decreased as the percentile of normal performance defining impairment increased. Estimated excess prevalence of impairment, defined as performance below the 5th percentile of normal, after 2 years of exposure at the current California standard (0.2 mg/m 3, 8 h TWA), ranged 15–32% for the outcomes studied. Because these exposures occurred over a 1–2-year period, generalization to lifetime excess risk requires further consideration of the form of the exposure response and whether short-term responses can be generalized to equivalent 45-year period. These results indicate unacceptable risks at the current OSHA PEL for manganese (5.0 mg/m 3, 15 min) and likely at the Cal OSHA PEL as well.

Geotechnical Design of Large Diameter Impact Driven Pipe Pile Foundations: New East Span San Francisco-Oakland Bay Bridge

The San Francisco-Oakland Bay Bridge is one of the most heavily travelled bridges in the world. The east span of the bridge will be replaced due to seismic safety concerns. The new bridge will be founded mostly on large 1.8 to 2.5-metre diameter, approximately 60- to 100-metre long pile foundations. Pile foundations will experience tension loads of up to approximately 90 MN and compression loads of approximately up to 140 MN during the design earthquake. This paper discusses the geotechnical design approach and techniques followed to evaluate the soil-pile-setup with time and the axial capacity of large diameter impact driven pipe piles for the project.

Closure to “Suspension Cable Design of the New San Francisco–Oakland Bay Bridge” by John Sun, Rafael Manzanarez, and Marwan Nader

This article presents a closure to a discussion by H. Knox of a paper with the aforementioned title. The original paper was published in this journal (Volume 9, Number 1, January/February 2004) and the discussion was published in this journal (Volume 10, Number 3, May/June 2005). The authors believe that their proposed octagon strand arrangement for the San Francisco-Oakland Bay Bridge is an effective way to alleviate potential strand twist. Space limitations in the original paper prevented presentation of some of the other issues that concerned the discusser, such as the lack of design details of strand separators in the saddles and the limited clear space between a strand socket and its anchor rod. The authors do present a possible solution to a problem concerning cable strand geometry during erection stages.

Discussion of “Suspension Cable Design of the New San Franscisco–Oakland Bay Bridge” by John Sun, Rafael Manzanarez, and Marwan Nader

A discussion of a paper with the aforementioned title by J. Sun et al., published in this journal (Volume 9, Number 1, January/February 2004), is presented. The discusser suggests that the octagon strand arrangement, proposed in the original paper to deal with some of the problems created by the unusual cable geometry of the San Francisco-Oakland Bay Bridge, may lead to other difficulties in construction. He also expresses concern about the lack of design details of strand separators in the saddles, cable strand geometry during erection stages and its relationship to the cable final position, and the limited clear space between a strand socket and its anchor rod. He concludes that these problems would make this a very difficult and expensive bridge to build.

Influence of Inelastic Tower Links on Cable-Supported Bridge Response

A new concept for bridge tower designs in seismic zones incorporates sacrificial link schemes that enable the tower shafts to remain elastic under large seismic excitation. In order to study the influence of inelastic tower links on the seismic response of cable-supported bridges, global seismic time history analyses were performed on models of the new San Francisco-Oakland Bay Bridge East Span self-anchored suspension bridge (SASB) and a cable-stayed bridge (CSB) alternative. The addition of inelastic links to the signature tower improved the behavior of both structures. The tower and overall bridge demands were reduced, including the tower drift and moments as well as the suspension cable, cable stay, and superstructure drifts and axial loads. The inelastic tower links protected the SASB and CSB tower shafts from nonlinear behavior under the 1,500-year Safety Evaluation Earthquake (SEE) event as well as a 2,500-year event. When the inelastic tower links were removed, the SASB tower shafts yielded under the SEE. It was shown that the inelastic tower links could be used to tune the dynamic response of bridge towers in regions of high seismicity.

Proof testing in support of the new San Francisco–Oakland Bay Bridge

AbstractFollowing the Loma Prieta earthquake, Caltrans (California Department of Transportation) started a multi‐year seismic vulnerability assessment and retrofit project of all major bridges in California, including the San Francisco–Oakland Bay Bridge (SFOBB) East Bay Span. First, a retrofit of the East Span Steel Truss structure was evaluated. However, owing to the high cost and the questionable reliability in terms of performance of the retrofit and owing to its difficult implementation under full traffic, a replacement structure was determined to provide a seismically more reliable alternative, resulting in the SFOBB East Span Replacement Project.The new bridge consists of four distinct structures: (1) the Oakland landing or touchdown structures; (2) a segmental concrete box girder crossing called the Skyway; (3) a self‐anchored suspension (SAS) signature span; and (4) a series of multi‐cell post‐tensioned concrete box girder bridges providing the transition to the tunnel on Yerba Buena Island. The new bridge will feature parallel roadways and will be built next to the existing bridge, which will be dismantled after the new bridge is opened to traffic.This paper focuses only on the seismic safety aspects in the RC elements of three of the four segments of the new SFOBB East Span Bridge, namely the Skyway, the SAS bridge and the Oakland touchdown. Analytical and numerical models were developed to assess the seismic behavior of the Bay Bridge and a large‐scale proof‐testing program was conducted at the Charles Lee Powell Structural Research Laboratories at the University of California, San Diego. In the framework of this program, two steel shear links at 100% scale were tested, two concrete piers of the Skyway at 25% scale, a 25% scale model of the West Anchor Pier W2, and two column 35% scale piers of the Oakland Touchdown were also tested.The large‐scale tests on all structural elements of the new East Span of the San Francisco–Oakland Bay Bridge with expected inelastic performance characteristics proved that the design fully meets all performance requirements. The large‐ or full‐scale tests were able to identify performance issues, resulting in design improvements and considerable cost savings. Alternative detailing and construction procedures were validated, leading to a more economic construction of the new bridge. Copyright © 2005 John Wiley & Sons, Ltd.

Performance evaluation of shear links and orthotropic bridge deck panels for the new San Francisco–Oakland Bay Bridge

AbstractThis paper presents results from testing and the associated analytical studies of steel shear links and orthotropic bridge decks to support the design of the new East Span for the San Francisco–Oakland Bay Bridge. Cyclic testing of full‐scale built‐up links showed that the specimens were able to reach an inelastic rotation more than twice that which would be produced from a 1500‐year Safety Evaluation Earthquake event. Nevertheless, brittle fracture occurred before the inelastic design rotation capacity, as specified in the AISC Seismic Provisions, was developed. Based on a parametric study, a modification to the welding details was proposed, which proved to be effective in preventing this type of fracture in a subsequent testing program. Monotonic testing of two reduced‐scale orthotropic bridge deck panels, one stiffened with closed ribs and another one with open ribs, also showed that these specimens could develop a compression capacity greater than that which would be produced by the design earthquake. The post‐buckling behavior was associated with the buckling direction and the type of ribs. Copyright © 2005 John Wiley & Sons, Ltd.

Development of built-up shear links as energy dissipators for the seismic protection of long-span bridges

The proposed new east bay crossing of the San Francisco – Oakland Bay Bridge (SFOBB) will use steel shear links as energy dissipators for added protection during strong earthquakes. These large-capacity, built-up shear links are embedded at various heights in the tower, which comprises four vertical steel shafts that are cantilevered from the pile cap. Although A709 HPS 70 steel is used throughout the bridge, the shear links use A709 Grade 50 steel, due to a lack of data regarding the inelastic performance of the HPS 70 steel at large plastic strains. Inelastic shear links have been used in building construction for many years but their application to bridge structures is still in its infancy. For this reason, the California Department of Transportation (Caltrans) funded both full-scale and half-scale tests of the proposed SFOBB shear links. The full-scale test was carried out at the University of California in San Diego, and the half-scale test, which included sections of the adjacent tower shafts, was c...

Design of Skyway Structures for California's San Francisco-Oakland Bay Bridge

The seismically vulnerable eastern spans of California's San Francisco-Oakland Bay Bridge are being replaced with a dual, 3.6-km-long parallel structure. The skyway section, which consists of 2.1-km-long twin viaducts, is under construction by a joint venture of Kiewit, FCI, and Manson. The viaducts are precast segmental bridges erected in balanced cantilever, with a typical span of 160 m. The foundation consists of six 2.5-m-diameter pipe piles 100 m in length with a steel pile cap that is in-filled with concrete. The precast segments for the superstructure, which are as heavy as 7 MN, are lifted into position with self-launching winch lifters and are posttensioned. The bridge is situated between the Hayward and the San Andreas Faults, which can generate large earthquakes. Performance criteria require the bridge to be operational after a 1,500-year-return-period earthquake from either of these two faults.

Design of California's New San Francisco—Oakland Bay Self-Anchored Suspension Bridge

The seismically vulnerable east span of California's San Francisco—Oakland Bay Bridge will be replaced with a dual eastbound and westbound parallel structure 3.6 km long. The Bay Bridge lies between the Hayward and the San Andreas Faults, which can generate magnitude 7.5 and 8.1 M earthquakes, respectively. Performance criteria require that the bridge be operational immediately after a 1,500-year-return-period earthquake from either of these two faults. Four distinct structures will make up the bridge crossing: a low-rise posttensioned concrete box girder near the Oakland shore, a segmental concrete box girder 2.4 km long, a self-anchored suspension signature span, and a posttensioned concrete box girder that connects to the east portal of the Yerba Buena Island tunnel. The single-tower asymmetric self-anchored suspension bridge was selected from a total of four design alternatives that were developed for the signature main span; these included two cable-stayed bridges and two self-anchored suspension bri...