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This paper presents a case study on the seismic response of a recently constructed freeway overcrossing located in southern California, which is equipped with elastomeric bearings and fluid dampers at its end abutments. The analysis employs the substructure method and a reduced order stick model. The macroscopic constitutive laws of the springs and dashpots that approximate the mechanical behavior of approach embankments, pile foundations, center bent, abutments, elastomeric bearings, and fluid dampers are established in the companion paper. The paper presents an in-depth analysis of the seismic response of the bridge equipped with the response modification devices accounting for the effects of soil–structure interaction. The various response quantities presented are compared with the corresponding response quantities of a hypothetical bridge with integral abutments. Advantages and challenges in the two design configurations are identified and discussed. [ABSTRACT FROM AUTHOR]

This paper focuses on the benchmark control problems for seismically excited nonlinear buildings. The benchmark study focuses on three typical steel structures, 3-, 9-, and 20-story buildings designed for the SAC project for the Los Angeles region. This paper reports the application of the active control scheme on the 3- and 20-story benchmark buildings, where the control action is achieved by a fuzzy logic controller. The main advantage of the fuzzy controller is its inherent robustness and ability to handle any nonlinear behavior of the structure. The performance of the controller is validated through the computer simulation on MATLAB. The control scheme satisfies the control constraints and is presented according to the evaluation criteria provided with the benchmark problems for comparison with other schemes. Four different earthquakes (El Centro 1940, Hachinohe 1968, Northridge 1994, and Kobe 1995) will be used in the simulation. [ABSTRACT FROM AUTHOR]

California Civil Code §§895 through 945.5, also known as “SB 800,” has dramatically changed the legal landscape for residential construction projects in California. The law sets forth new, legislatively defined, actionable defects; a detailed prelitigation repair process; and available damages and defenses. This paper examines the impacts of the law on design professionals and concludes that the law appears to have supplanted the standard of care for design professionals in connection with residential construction—meaning that their services may now be measured against codified standards instead of against the performance of their peers. Alternatively, rather than supplanting the standard of care, the law may have the practical effect of shifting the burden of proof from homeowner claimants to the allegedly negligent design professionals, thereby requiring the defendant design professional to show that their services comply with the standard of care in order to escape liability. In either event, the playing field has changed dramatically for design professionals. This paper suggests ways in which design professionals might tailor their practices to best position themselves for claims which are sure to arise out of SB 800. [ABSTRACT FROM AUTHOR]

The Borax corporate headquarters building, a low-rise steel moment frame, was less than one year old when it sustained significant structural damage during the 1994 Northridge earthquake. Seventy-five percent of its steel moment-resisting connections suffered severe brittle fractures. This paper presents a detailed documentation of the forensic investigation performed on this structure immediately following the earthquake. A companion paper presents the findings from a subsequent computational investigation performed on the structure. The two primary failure modes at the Borax building were column flange fracture and pull-out of the girder flange from the column. The failures are primarily attributed to a fundamental flaw in the standard code-prescribed welded-flange bolted-web connection and the extreme ground motion at the site. The paper also describes the repairs made to the structure. These repairs were completed before the SAC research that now guides repair and retrofit of these structures was available. [ABSTRACT FROM AUTHOR]

This paper presents the findings from a computational investigation performed on the Borax corporate headquarters building, a four-story steel frame structure in which 75% of the steel moment-resisting connections suffered brittle fractures during the 1994 Northridge earthquake. A companion paper provides detailed documentation of the forensic investigation and repair design performed immediately following the earthquake on this structure, which was less than one year old when the earthquake struck. This paper describes a series of preliminary analyses conducted shortly after the forensic investigation and repair were completed. The main objectives were to investigate the behavior of the structure during the earthquake, and to determine whether different levels of established, advanced analysis techniques could estimate the distribution and extent of the damage. The results showed that a three-dimensional nonlinear dynamic analysis using a site-specific accelerogram provides strong correlation with the observed damage, while elastic static and dynamic analyses, two-dimensional nonlinear static and dynamic analyses, and three-dimensional nonlinear static analyses show less correlation. In addition, the results indicate that substantial redistribution of forces may have occurred, and that force distribution most likely had a noticeable effect on the pattern of failures observed in the structure. [ABSTRACT FROM AUTHOR]

Tidal wetlands in California are mostly estuarine salt marshes characterized by tidal channels and mudflats that are flooded and drained on a semidiurnal basis. Depths are rarely greater than 2 or 3 m, except where dredging occurs for harbor operations, and lengths from head to mouth are usually in the range of 1–10 km. This paper presents a coupled set of models for prediction of flow, solute transport, and particle transport in these systems. The flow and solute transport models are based upon depth-integrated conservation equations while the particle transport model is quasi-three-dimensional. Common to these models is an assumption that a turbulent boundary layer extends vertically from the bed and can be described by the law of the wall. This feature of the model accounts for: (1) momentum transfer to the bed, (2) longitudinal dispersion of dissolved material based on the work of Elder (1959), and (3) advection and turbulent diffusion of particles in three dimensions. A total variation diminishing finite volume scheme is used to solve the depth-integrated equations. Using this model, we show that dispersion can be accurately modeled using physically meaningful mixing coefficients. Calibration is therefore directed at modifying bed roughness, which scales both the rate of advection and dispersion. [ABSTRACT FROM AUTHOR]

This paper presents results of a large-scale economic-engineering optimization model of California’s water supply system. The results of this 4-year effort illustrate the value of optimization modeling for providing integrated information needed to manage a complex multipurpose water system. This information includes economic benefits of flexible operations, economic valuation of capacity expansion opportunities, estimating user willingness to pay for additional water, economic opportunity costs of environmental flows, and identification of promising conjunctive use and water transfer opportunities. The limitations of such modeling also are discussed. Overall, the results suggest improvements to system operation and water allocations with a statewide expected value potentially as high as $1.3 billion/year. Significant improvements in performance appear possible through water transfers and exchanges, conjunctive use, and various operational changes to increase flexibility. These changes also greatly reduce costs to agricultural and urban users of accommodating environmental requirements. Model results also suggest benefits for expanding selected conveyance and storage facilities. [ABSTRACT FROM AUTHOR]

There is a prevailing assumption that Freeway Service Patrol (FSP) programs improve safety for unassisted motorists by reducing the likelihood of secondary accidents. This research identifies 84,684 accident records from the California Highway Patrol’s First Incident Response Services Tracking system, and subjects these data records to a sequence of filters that check for incrementally more stringent conditions consistent with secondary accidents. This paper shows that secondary accidents on Los Angeles freeways are much less frequent than suggested in the transportation engineering literature. Avoiding secondary accidents provides only a small incentive to deploy FSPs, but the expected benefits associated with reducing already low secondary accident rates may still be sufficient to justify accounting for these costs. [ABSTRACT FROM AUTHOR]

During the 1989 Loma Prieta earthquake the Pajaro River levees near Watsonville, Calif., spread laterally at multiple locations. Four of these locations are discussed in this paper. At one location, an industrial facility was also damaged and a dispute arose as to whether lateral spreading of the adjacent levee was the cause. Stability analyses were made of the industrial site for conditions before, during, and after the earthquake. To confirm the findings, analyses were also made of three other nearby locations where the actual deformation was documented and the subsurface conditions are well defined. The calculated levee deformations at the four locations are quite consistent with the observed movements (up to 60 cm). This experience provides increased confidence in the methods of analysis described, for the characterized subsurface conditions, and the range of ground motions experienced. Additional analyses made using the more recently developed multilinear regression lateral-spreading model (e.g., Youd et al. in 1999) yielded inconsistent results. [ABSTRACT FROM AUTHOR]

Urban sprawl makes conventional transit less competitive and points to the need for more innovative and flexible demand-responsive transit systems in the future. To increase their efficiency, such systems can take advantage of the emerging advanced public transportation systems technologies, e.g., vehicle location and information systems. However, little is known about how consumers might respond to such systems and what they desire. This paper explores the demand for a consumer-oriented Personalized Demand-Responsive Transit (PDRT) service in the San Francisco Bay Area. Such a system could provide services to the traveling public for journeys to work and to nonwork destinations. Results from six focus group meetings and a computer-assisted telephone survey of commuters and noncommuters are reported. While about 60% of those surveyed were willing to consider PDRT as an option, about 12% reported that they were “very likely” to use PDRT (N=1,000). Many were willing to pay for the service and valued highly the flexibility in scheduling the service. Spatial analysis of the survey responses suggests localities where a PDRT may be field-tested. [ABSTRACT FROM AUTHOR]

In response to the destructive floods of 1983, 1986, 1995, and 1997, the U.S. Army Corps of Engineers and the Reclamation Board of the State of California are partnering a study to investigate flood damage reduction and ecosystem restoration opportunities in the Sacramento and San Joaquin River Basins, California. This paper continues presentation of Comprehensive Study methods and details the construction and application of basin-wide reservoir models in support of ongoing system analyses. Discussion emphasizes model development, simulation results with a focus on headwater and major terminal reservoirs, and potential improvements to the flood damage reduction system. Conclusions are drawn regarding the influence of reservoirs in flood hydrology, use of HEC-5 software in flood analyses, and the role of this effort in the Comprehensive Study. [ABSTRACT FROM AUTHOR]

TransGuide is San Antonio’s multifunctional citywide center that manages traffic through surveillance, incident detection/management, and dissemination of traffic information. This paper reviews automatic incident detection technologies deployed in San Antonio freeways and managed by TransGuide. Traffic and incident data collected from the San Antonio network are used to compare the performance of inductive loop detectors (ILDs) and automatic vehicle identification (AVI) for automated incident detection. California No. 8 and the Texas algorithms were calibrated and tested using the ILD data collected for incident detection. The upper confidence limit algorithm and the Texas algorithm were calibrated and tested using the AVI data collected. When traffic and incident data from the San Antonio network are processed by the four different algorithms, the California No. 8 algorithms applied to ILD data performed best in terms of detection rate and false alarm rate. Automated incident detection (AID) is not currently worth implementing in the AVI system studied, but AID based on AVI data is generally feasible with denser tag penetration and sensor installation. [ABSTRACT FROM AUTHOR]

Load estimation is an important component of watershed analysis and management, particularly in light of the Total Maximum Daily Load program set forth by the Clean Water Act. This paper addresses load estimation in tidally driven channels that are dominated by advection and well mixed over the channel cross section. Such systems are common in Southern California, and represent an important link between watersheds and the coastal ocean. The oscillating flow field of tidal channels calls for a time series of data (volumetric flow rate and scalar concentrations! sampled at a sufficiently high frequency to resolve the net load of each scalar. Results of an experiment conducted in the Talbert Channel in Huntington Beach, California, to quantify freshwater loads suggest that sampling should be conducted at a minimum frequency of 0.5/h. In this system, traces of freshwater were detected in the channel by salinity depressions that ranged from 1-7 ppt and lasted 4 -6 h. The freshwater load was computed as the integral of the volumetric flow rate multiplied by the freshwater fraction of the water column. Based on the duration of these events and the 0.5/h sampling frequency, these results suggest that loads will be resolved to a reasonable level of accuracy when each event is captured by at least three or four data points. Strategies to estimate the flow rate and scalar concentrations are discussed. [ABSTRACT FROM AUTHOR]

A seismic retrofit program at Yerba Buena Island Tunnel is presented as a case history. The studies include evaluations of portal stability under earthquake excitation and performance of the tunnel liner as a result of seismic induced deformation. Due to different potential failure modes at the two portal areas, two separate evaluation techniques were utilized. Key block theory in conjunction with a Newmark type analysis was used to assess movements of a potential failure wedge at the west portal slope, while discontinuous deformation analysis was utilized at the east portal slope to evaluate a rotational mode of failure. To assess the performance of the liner subjected to design earthquakes, a two-step analysis procedure was adopted. The first step was to compute seismic induced deformations of the tunnel subjected to seismic wave propagation through the island rock without the presence of the liner. The second step, not reported in this paper, involved imposing the deformations of the tunnel onto the structural liner through spring elements that accounted for interaction between the liner and the surrounding rock. From the studies, performance of the existing tunnel supports was found to be acceptable. [ABSTRACT FROM AUTHOR]

This paper examines the institutional origins and functioning of the Monterey County Water Recycling Project (MCWRP), a centralized tertiary-treatment facility that began operating in April, 1998, and delivers urban recycled water to growers at the mouth of the Salinas River, a site of extensive seawater intrusion to coastal aquifers. The Salinas Valley supports extensive irrigated agricultural production and several towns. The MCWRP was established with the cooperation of federal, state, regional, and local authorities. Federal sources financed roughly 70% of the initial capital costs, while local authorities own and manage the project. In turn, growers receive urban recycled water and pay acreage fees. Reasons for the success of this project include cost sharing among all beneficiaries, devolution of sufficient authority to regional and local authorities to impose alternative solutions, federal and state financial support, and development of innovative project management institutions. Future challenges could arise from increasing competition for all water supplies in the region. [ABSTRACT FROM AUTHOR]

This paper presents a seismic evaluation of the San Carlos airport traffic control tower ATCT! in San Carlos, California, that describes the tower, presents the seismic evaluation of the tower, and defines a rehabilitation approach that upgrades the structure to applicable life-safety standards. The San Carlos ATCT is a Federal Aviation Administration Type L tower, whose primary structure below the control cab tower shaft! is four inverted L-shaped reinforced concrete members that frame together at the top of the tower shaft. The cab structure is a steel-moment frame. The tower was analyzed with a finite-element model using a response spectrum linear analysis. The goal of this evaluation was to determine if life-safety performance could be demonstrated, and if not, to develop an upgrade approach to achieve this performance. The seismic hazard was based on the maximum considered earthquake defined in the National Earthquake Hazards Reduction Program NEHRP! recommended provisions. The evaluation shows that the tower cannot achieve life-safety perfor-mance due to large deflections in the cab and the formation of a collapse mechanism. The connection base plates for the cab columns corner window mullions! will form a collapse mechanism at very low seismic motions. Formation of the collapse mechanism is due to base-plate bending failure and subsequent hinging at the base of each column. The recommended rehabilitation approach is to upgrade the columns to reduce deflections to acceptable levels, and also to protect the vulnerable connections. Upgrading the columns consists of welding plates on the interior and exterior column faces and welding deep structural tubing members to the base of each corner column. The writers considered the evaluation of this particular control tower to be of interest to the technical community because of the unique failure mechanism and proposed upgrade approach. [ABSTRACT FROM AUTHOR]

This paper presents an overview of training academies on horizontal directional drilling (HDD) conducted for the education and training of 125 resident engineers and permit inspectors for the California Dept. of Transportation, 54 utility inspectors, 16 consultants, and 26 city/county Inspectors. Each of the four academies took place over a 3-day period during which the first and third days involved intense classroom preparation. The second day provided field experience through demonstrations of various equipment and construction methods used in HDD. A pretest was administered on the first day, prior to any instruction, followed by a final test administered at the end of the last day. A grade of 70% or better was required to pass the course. The overall average of all 221 participants was 75.27% with a standard deviation of 8.10%. Further analysis of the test results concluded that level of formal education did not have any significant effect on the final grade obtained in the course. In addition, the average grade of each academy increased slightly with each subsequent academy. The improved scores could be a function of the quality of the class as well as the quality of instruction with each academy. [ABSTRACT FROM AUTHOR]

Concern over possible inequities in the siting of noxious facilities leads us to study spatial patterns of distribution of hazardous waste treatment, storage, and disposal facilities (TSDs). Inasmuch as such patterns are inextricably linked to particular land-use institutions, our focus is jurisdiction-specific, in this case, concentrated on the city of Los Angeles. Problems with statistical confounding require some effort at ordinary least-squares model specification and diagnostics. The paper addresses the simultaneity of effects due to demographics and zoning, and we employ a two-stage least-squares procedure to address the possibility that both the siting and industrial zoning are endogenously determined. The results suggest a significant correlation between prevalence of TSDs and the proportion of Latino residents. The political implications of such results are unquestionable, and analyses such as this can be used in conjunction with a greater body of evidence supporting the call for reform. We show how the statistical analysis might also be useful for formulating fair-share criteria for screening locations in the site selection/screening process. [ABSTRACT FROM AUTHOR]

On October 17, 1989, the Loma Prieta earthquake took place near Santa Cruz, Calif. Damage occurred as far as 100 km from the earthquake's epicenter. Of particular concern was damage to transportation systems and widespread disruption of utilities and lifeline facilities. Damage to airports in the vicinity of a major natural disaster, such as the Loma Prieta earthquake, is critical because airports are a major link in our national transportation system that can deliver emergency supplies and help. An investigation into a case history such as the damage that occurred at the Metropolitan Oakland International Airport provides valuable experience. The damage that occurred to the runway pavement was a result of liquefaction occurring in an underlying zone of dredged sand fill. Only the western 900 m of the 3,000-m Runway 11-29 was significantly damaged. This paper discusses the conditions that led to the failure of 900 m of Runway 11-29, describes the damage that occurred, and summarizes the repairs that were made to the runway. [ABSTRACT FROM AUTHOR]

This paper reviews the performance of welded steel moment frame buildings during the Northridge earthquake. Some of the studies being undertaken in the United States as part of the FEMA-funded SAC Steel Project are described. The intent of these studies is to devise improved methods for designing new steel frame structures; for inspecting, evaluating, and repairing seismic damage to these types of structures following a major earthquake; and for inspecting, evaluating, and retrofitting existing at-risk steel frame buildings. General observations resulting from these studies are highlighted and the overall format for the new design provisions is presented. [ABSTRACT FROM AUTHOR]

This paper summarizes the review and interpretation of data collected on welded steel moment frames (WSMFs) that were damaged in the January 17, 1994, Northridge Earthquake. The study was part of the Phase I, Task 2 SAC Steel Project funded by the Federal Emergency Management Agency. The data assessment included 89 WSMFs surveyed by structural engineers, 150 buildings covered under a survey of owners, and ground motion contour maps with the geographic distribution of all WSMF buildings surveyed. Data collected from interviews with the structural engineers familiar with the buildings and their locations were used to independently validate the database and provide guidance on its interpretation. General conclusions on the significant trends in the data are presented, along with suggested future (Phase II) data gathering and statistical analysis. [ABSTRACT FROM AUTHOR]

Summarized in this paper are the major findings from analytical studies of nine steel moment frame buildings conducted under Phase 1 of the SAC Steel Project. The buildings range in height from two to seventeen stories and most of them experienced damage to welded beam-column connections during the Northridge earthquake of 1994. Elastic response spectrum, inelastic static pushover, and elastic and inelastic time-history analyses were conducted using ground motion data representative of the Northridge earthquake to establish the loading/deformation demands that the buildings experienced. The primary performance indices obtained from the analyses were demand-to-capacity ratios, interstory drift ratios, and inelastic hinge rotations. Maximum ratios of elastic member force demands to plastic strengths ranged between 1.0 and 2.0; maximum inelastic hinge rotations were 0.005–0.010 rad; and maximum interstory drift ratios were from 1 to 2%. These damage indices increased by 50%–150% under more severe ground motions recorded during the Northridge earthquake at the Sylmar site. Accuracy of the analyses is shown to be sensitive to a number of modeling parameters including finite joint size, joint panel behavior, composite beam action, strain hardening, second-order (P-Δ) effects, and three-dimensional response. Overall, there was only modest correlation between the frame performance indices and the observed connection damage, due largely to the fact that significant aspects of the connection fracture behavior are not captured in the frame analyses. [ABSTRACT FROM AUTHOR]

Water-quality models to predict oxygen dynamics in streams require estimates of rates of reaeration, respiration, and primary production, which are often evaluated through diel studies. Simple, approximate methods of parameter estimation are desirable at the scoping level, and are often used for waste-load allocation studies. Scoping methods often assume that reaeration and respiration are constant over the diel period. Use of such methods, however, can yield unrealistic parameter estimates for shallow streams with a significant range of diel water temperatures, because both reaeration and respiration rates as well as the saturation concentration of dissolved oxygen are temperature-dependent. Based on our work on the Santa Margarita River in Southern California, this paper presents a modified approach to dissolved-oxygen–rate parameter estimation that takes temperature variation into account. Using a simple finite-difference approximation, temperature-normalized parameter estimates are readily optimized in a spreadsheet application. The approach is applicable to many shallow streams in which diel temperature variability is significant. [ABSTRACT FROM AUTHOR]

This paper describes the failure of the Desert View Drive fill embankment in La Jolla, Calif. The embankment was built in late 1960 or early 1961. Other than a report of surficial instability in 1977, the embankment was marginally stable (factor of safety of 1.15) until 1990, when an excavation group cut into the embankment to construct a building pad and house. The resulting failure of the Desert View Drive fill embankment was a progressive failure, starting as a circular mode and eventually increasing to a wedge type movement of the entire fill embankment. The legal theories used as the basis to sue the city of San Diego were that (1) the city officials were aware of the defective condition (poor compaction) of the embankment, but they did not fix this condition; and (2) they failed to provide subjacent support to the homeowners property. The repair of the fill embankment consisted of the construction of 40 massive piers anchored in the underlying Ardath shale. [ABSTRACT FROM AUTHOR]

A sampling design methodology for monitoring contaminant distribution in lake sediments is presented in this paper. Two optimization approaches are employed: a minimization of the variance of estimation approach and a sampling cost minimization approach, allowing an economically efficient sampling design and a decision-making tool given the multiobjective nature of the problem. The geostatistical method of cokriging is used as a tool on which the proposed sampling design is based. The adopted technique incorporates spatial as well as intervariable correlations, to improve the prediction and estimation of sampled quantities. The methodology is applied to Clear Lake, California, to design a network for sampling mercury concentrations in lake sediments. The network design takes advantage of the cross correlation between the mercury concentrations and sediment grain size index. A sensitivity analysis is carried out to assess the sensitivity of the solution to the optimization model inputs. [ABSTRACT FROM AUTHOR]

Editorial. Focuses on the behavior of welded connections in building structures when subjected to strong ground shaking during severe earthquakes. Problems discovered following the 1994 Northridge earthquake in California; Introduction of several papers on the behavior and design of steel weldments.