Editor’s Note

This issue of the Journal begins with a paper of interest to practicing engineers and DOTs inspecting bridges with scour vulnerability. “Bridge Scour and Substructure Deterioration: A Case Study,” by R. Richard Avent and Mohamed Alawady, provides a case study of two bridges that were found during inspection to have both significant scour and substructure deteriorations. Despite repairs, the deterioration continued. The paper describes how the bridge-waterway system responded to the modifications during the 12 years since the damage was first discovered.

The next paper, by Fanous and Wu and titled “Performance of Coated Reinforcing Bars in Cracked Bridge Decks,” describes an investigation performed by bridge and maintenance engineers in the State of Iowa. Some of the bridge decks that were cracked had been reinforced with epoxy-coated reinforcing bars. These cracks raised concerns and resulted in the collection of core samples containing reinforcing bars from 80 bridges, both cracked and uncracked, located throughout the state. The study did not find evidence of reinforcing bar corrosion in samples taken from the uncracked decks, and no delamination or spalling was found for samples taken from cracked decks where the reinforcing bars were exhibiting signs of corrosion. A rating system was developed based on condition-age relationships in order to estimate the functional service life of bridge decks reinforced with epoxy-coated reinforcing bars.

The third paper, “Reliability Analysis of Suspension Bridges against Fatigue Failure from the Gusting of Wind,” by Pourzeynali and Datta, presents their work on reliability analysis for suspension bridges comparing the first-order second-moment (FOSM) method versus the full distribution procedure (assuming Weibull distribution of fatigue life). The analysis combines overall concepts of bridge aerodynamics, fatigue analysis, and reliability analysis, and presents the probabilities of fatigue failure of the Thomas Bridge and the Golden Gate Bridge for a number of important parametric variations in order to develop some general conclusions on the fatigue reliability of these types of structures. The results of the study indicate that the FOSM method predicts a higher value of the probability of fatigue failure as compared with the full distribution method, and in addition, the distribution of stress range used in the analysis has a significant effect on the probability of fatigue failure.

“Influence of Inelastic Tower Links on Cable-Supported Bridge Response,” by McDaniel and Seible, investigates the use of sacrificial links that enable the tower shafts to remain elastic under large seismic loads. This is a new concept for bridge tower designs in seismic zones. Global seismic time-history analyses were performed on models of the new San Francisco–Oakland Bay Bridge East Span and a cable-stayed bridge alternative. The analysis found that the addition of inelastic links to the signature tower improved the performance of both structures, protecting the tower shafts from nonlinear behavior under the 1,500-year Safety Evaluation Earthquake event as well as a 2,500-year event. In addition, the inelastic links could be used to tune the dynamic response of bridge towers in regions of high seismicity.

The next two papers are on the subject of steel I-girder bridges. In “Lateral Load Distribution in Curved Steel I-Girder Bridges,” Zhang et al., show the development of new formulas for live load distribution in horizontally curved steel I-girder bridges. Using computer models based on generalized grillage beam systems composed of horizontally curved beam elements to develop the formulas, the authors identified key parameters affecting live load distribution, and simplified formulas were developed to predict positive moment, negative moment, and shear distribution for one-lane and multiple-lane loading. The authors show that these formulas are more accurate than those available in the AASHTO Specifications.

“Optimum Design of Welded Steel Plate-Girder Bridges Using a Genetic Algorithm with Elitism,” by Fu et al. uses the Genetic Algorithm, a general optimization technique, to find the optimum design of welded steel plate-girder bridges. The paper presents the results of applying this technique to two example plate-girder bridges.

The seventh paper, by Pisani, “Geometrical Nonlinearity and Length of External Tendons,” provides a simple equation to determine the maximum clear length of a tendon. This equation eliminates the need to take into account second-order effects as a result of the deformed shape of a concrete beam, significantly changing the location of its section properties in relation to the location of externally tendons.

Li et al., in “Vibration Control of Railway Bridges under High-Speed Trains Using Multiple Tuned Mass Dampers,” examines the effectiveness of using multiple tuned mass dampers (MTMD) to suppress the resonant vibration of railway bridges. The investigation reveals that the MTMDs can significantly reduce the displacement and acceleration responses of railway bridges.

The ninth paper of this issue of the Journal of Bridge Engineering is of interest to practicing engineers and DOT engineers. “Impact of Posted Load Limits on Highway Bridge Reliability,” by Asantey and Bartlett, investigates the effectiveness of posted load limits in reducing annual maximum live load effects, and thus the reliability of bridges. The authors compute annual reliability indices using typical posting criteria and different compliance levels. The results indicate that unless posted loads are strictly enforced, the effectiveness of improving existing bridge reliability with a posted load restriction is questionable.

In “Behavior, Analysis, and Design of an Instrumented Link Slab Bridge,” Wing and Kowalsky present the results of a research project on the monitoring and assessment of the first link-slab jointless bridge in North Carolina. The results determined that while the crack size in the link exceeded the design limits, the slab satisfactorily performed its function.

The next paper, “Vehicle Collision with Bridge Piers,” by El-Tawil et al., investigates the loads and demands generated on bridge piers when subjected to vehicle collisions. The work was based on inelastic transient finite-element simulations using two different types of trucks and two different bridge∕pier systems. Based on the simulations, the authors conclude that the current collision design provisions may not provide an adequate design or assessment of bridge piers subjected to these loads.

The final paper for this issue, “Integral Abutment-Backfill Behavior on Sand Soil-Pushover Analysis Approach,” by Dicleli, presents a study of the behavior of integral abutment systems built on sand. The work is based on building a structural model treating the piles and soil-bridge interaction as nonlinear. The work found that the shape and magnitude of the backfill pressure is affected by the height of the abutment and that the forces in the abutment are functions of thermal-induced longitudinal movement of the abutment, properties of the piles, and the density of the sand around the piles. The paper concludes it is desirable that these types of abutments be constructed with the piles encased in loose sand, that the piles be oriented to bend about their weak axis, that the abutment height be less than four meters, and that noncompacted backfill be used.

There is a discussion and a closure in this issue. The discussion and closure are in regard to “Suspension Cable Design of the New San Francisco–Oakland Bay Bridge,” by Sun et al. In his discussion, Hugh S. G. Knox suggests that the proposed octagon strand arrangement may lead to other problems, specifically the difficulty of compacting the cable into a circular shape. The discusser further notes that the paper does not make clear what is proposed to be used for separator plates in the saddles, and brings up other construction-related questions and issues.

In the closure for “Suspension Cable Design of the New San Francisco–Oakland Bay Bridge,” the authors address Mr. Knox’s questions and provide clarification for the proposed details and construction-related issues.