Editor’s Note

The September 2006 issue of the ASCE Journal of Bridge Engineering begins with four papers on the subject of bridge decks, with the first two about orthotropic decks. “Consistent Approach to Calculating Stresses for Fatigue Design of Welded Rib-to-Web Connections in Steel Orthotropic Bridge Decks,” by Connor and Fisher, presents the method of defining and determining the fatigue stress range for rib-to-web (or diaphragm) connections for orthotropic decks. The fatigue resistance was established through full-scale testing of the details. The paper also provides a procedure to calculate or measure the stresses at the rib-to-diaphragm connection. This procedure is consistent with the fatigue resistance published in the AASHTO LRFD Design Specifications.

The second paper is by Xiao, Yamada, Inoue, and Yamaguchi. In “Measurement of Truck Axle Weights by Instrumenting Longitudinal Ribs of Orthotropic Bridge,” the authors present their findings from instrumenting the longitudinal ribs of an orthotropic box-girder bridge to measure the axle weights of trucks. The authors instrumented the bridge and performed calibration tests to solve the influence lines of the girder and rib components at each strain gauge. With these influence lines, the rib component was separated from the girder, and the axle weights of the truck traffic could be calculated.

“Penetrating Sealants for Concrete Bridge Decks—Selection Procedure,” by Attanayake, Liang, Ng, and Aktan outlines a sealant selection procedure that incorporates available test methods that are based on knowledge gained through fundamental studies of flow phenomenon and the literature.

The final deck paper is by Ancich, Chirgwin, and Brown. In “Dynamic Anomalies in a Modular Bridge Expansion Joint,” the authors investigate the noise production mechanism for modular bridge expansion joints. The investigation identifies modal vibration frequencies in the joint coupling with acoustic resonances in the chamber cast into the abutment below the joint.

The fifth paper, “Capacity Evaluation of Exterior Sacrificial Shear Keys of Bridge Abutments,” is by Bozorgzadeh, Megally, Restrepo, and Ashford. This paper presents the experimental and analytical work conducted to investigate the seismic behavior of exterior shear keys in bridge abutments. This work resulted from the 1994 Northridge earthquake, in which it was noted that these external shear keys did not perform satisfactorily. The study concluded that a smooth construction joint should be considered at the interface of the shear key–abutment stem wall to allow sliding shear failure.

In “Posttensioned Anchorage Zone Enhancement with Fiber-Reinforced Concrete,” Haroon, Yazdani, and Tawfiq present the results of an investigation into the feasibility of reducing the secondary reinforcement in the posttensioned anchor zones with steel-fiber-reinforced concrete. The posttensioned anchorage zone is highly congested with reinforcement, and it can be difficult to place concrete in this region. The experimental results indicated that 1% hooked-end steel fibers could eliminate all the secondary reinforcement normally used in this region.

“Live-Load Distribution Factors for Prestressed Concrete, Spread Box-Girder Bridge,” by Hughs and Idriss, presents the study of an evaluation of shear and moment live-load distribution factors for a new, prestressed concrete spread box-girder bridge. The distribution factors for shear and moment were measured under a live-load test by using embedded fiber-optic sensors and were used to verify a finite-element model. This model was then loaded with an AASHTO design truck. The resulting maximum girder-distribution factors were compared with those calculated by using both the AASHTO Standard Specifications and the AASHTO LRFD Bridge Design Specifications. The study found that the LRFD Specifications either accurately or conservatively computed the distribution factors on basis of the finite element model, whereas the Standard Specification–based distribution factors were either highly unconservative or highly conservative.

The eighth paper in this month’s issue of the journal is by Sagüés, Kranc, and Eason. “Vibrational Tension Measurement of External Tendons in Segmental Posttensioned Bridges” presents a rapid and economical vibrational tension measurement method to detect distress in external tendons used in segmental posttensioned bridges. The method is complementary to the traditional inspection methods that are typically used for these tendons. Example application of the technique on several bridges has shown that it can detect corrosion damage, improper tensioning, and force distribution effects from friction at deviation blocks.

Zanardo, Hao, Xia, and Deeks, in “Stiffness Assessment through Modal Analysis of an RC Slab Bridge before and after Strengthening,” present the evaluation of a bridge before and after strengthening with CFRP. The assessment process coupled analytical results with field observations and dynamic testing of the structure. The paper presents the results of the vibration tests and modal analyses performed before and after the structure was strengthened. The authors found that dynamic assessment could accurately determine the elastic flexural stiffness of bridge structures strengthened with CFRP.

Techniques that can continuously monitor in-service highway bridges are of major interest to departments of transportation. In “Ambient Vibration Monitoring of a Highway Bridge Undergoing a Destructive Test,” Lauzon and DeWolf studied the dynamic responses of a full-scale steel-girder highway bridge during the passage of a small truck. Measurements were taken before and during the stage introduction of a simulated crack in one of the main supporting girders. The results indicate that monitoring the amplitudes at the natural frequencies and the frequency response spectrum can be used as an indicator that significant cracks have developed in a multigirder highway bridge.

The recently developed Manual for Condition Evaluation and Load and Resistance Factor Rating (LRFR) of Highway Bridges provides an alternative procedure for evaluating the fatigue life of steel bridge structures. In “Comparative Study of Fatigue Provisions for the AASHTO Fatigue Guide Specifications and LRFR Manual for Evaluation” by Chotickai and Bowman, a comparative study of the fatigue lives provided by the procedures in the Evaluation Manual and the Guide Specifications was performed by using a life prediction of 14 steel bridges with different structural configurations and various fatigue details. The study found that the Evaluation Manual predicted longer fatigue lives.

In “Investigation of Longitudinal Forces in a Concrete Railroad Trestle,” Foutch, Kim, Otter, and Doe present the results of tests conducted on a long concrete trestle to quantify the longitudinal forces generated by a coal train with AC locomotives. The results confirmed the AREMA formula for forces attributable to traction. Testing determined the distribution of shear forces in bents and the equilibrium of the structure, in conjunction with an analytical model of the bridge structure. The primary finding was that the longitudinal force is transmitted to the trestle, but it is distributed to a large number of bents through many spans. Forces in individual bents are small compared with the total applied force.

“Short- and Long-Term Effects of Element Costs and Failure Costs in Pontis,” by Milligan, Nielson, and Schmeckpeper, presents their results in entering the estimated unit costs for Pontis bridge elements on the basis of costs in Idaho. The results were compared on the basis of costs provided by the California and Oregon departments of transportation. The differences in the results were examined and compared.

The second-to-last paper in this issue is also on the subject of bridge evaluation. Liu and Frangopol, in “Probability-Based Bridge Network Performance Evaluation,” present a comprehensive model for evaluating the overall performance of a bridge network on the basis of probability analyses of network connectivity, user satisfaction, and structural reliability of critical bridges in the network. The study provides the basis of a network-level bridge-management system for which lifetime reliability and life-cycle costs are the key considerations for optimal bridge maintenance strategies.

The final paper is another historical one by Griggs. “Development of the Vertical Lift Bridge: Squire Whipple to J. A. L. Waddell, 1872–1917” traces the development of bridges, in Europe and the United States and their evolution through various types of movable bridges, concluding with Waddell’s Columbia River Bridge in 1917.

There are two discussions in this issue of the journal. The first, by Weyers, discusses the paper “Performance of Coated Reinforcing Bars in Cracked Bridge Decks.” Weyers indicates that the paper’s authors should not have extended their investigation to estimating the service life of epoxy coated reinforcing, and he presents the basis for his conclusion.

The second discussion concerns the paper “Swaying of Pedestrian Bridges.” In his discussion, Ye discusses various aspects of the paper’s conclusions and presents additional information on the subject. The author, Blekherman, provides a closure to “Swaying of Pedestrian Bridges.” In this closure, the author addresses the issues raised in Ye’s discussion.