Editor’s Note

This issue of the Journal begins with several papers on the subjects of seismic and dynamic behavior or control of bridges. The first paper, “Wavelet-Hybrid Feedback LMS Algorithm For Robust Control of Cable-Stayed Bridges” by Kim and Adeli describes the use of a wavelet-hybrid feedback LMS (least mean squared) algorithm recently developed by the writers. The paper describes the investigation of the effectiveness of the algorithm’s use for vibration control of cable-stayed bridges under seismic excitation. The results of the investigation found that the algorithm was more effective and robust.

The next paper by Moroni, Boroschek, and Sarrazin titled “Dynamic Characteristics of Chilean Bridges With Seismic Protection” reviews the seismic experimental and analytical studies that were performed on new bridges built in Chile, a country with a high seismic risk.

“Dynamic and Impact Behavior of Half-Through Arch Bridges” by Huang presents the results of an investigation of the dynamic and impact characteristics from vehicles traveling on half-through arch bridges with rough decks. Seven arch bridges were investigated. The results of the analyses determined that the impact factors for bending moment do not exceed 0.4 and for axial force do not exceed 0.25. The writer proposes some simple and conservative impact equations that can be used for the design of half-through arch bridges.

“Swaying of Pedestrian Bridge” by Blekherman is the final dynamic paper in this issue. Nonlinear (autoparametric) resonance in footbridges is proposed as the reason for excessive lateral vibrations induced by pedestrians. The writer proposes the use of a physical model, an elastic pedulum, for the analysis and proposes that the swaying of pedestrian bridges can be treated as a two step process.

The next three papers are on the subject of bridge evaluation. In “Corrosion and Embrittlement in High-Strength Wires of Suspension Bridge Cables,” Betti, West, Vermaas, and Cao present an in-depth analysis of the deterioration mechanisms in high-strength wires found in suspension bridge cables. Accelerated cyclic corrosion tests were conducted to assess the relative effect of corrosion on galvanized and ungalvanized wires. The studies found that the elongation measurements indicated a significant embrittlement of the wires that could not be explained by hydrogen embrittlement. The elongation was determined to be the result of surface irregularities induced by the corrosion process. The experimental results were validated using FEM models and SEM analyses of the fracture surfaces.

The next paper, “Application of RTK-GPS in Bridge Safety Monitoring” by Guo, Xu, Dai, McDonald, and Wu, presents a real-time kinematic global positioning system that was developed and installed on the Humen Bridge in China for the monitoring of bridge deck movement resulting from either seismic activity, traffic load, and other environmental elements such as temperature and wind. The paper describes the features of the system and its value as a tool for safety monitoring.

The final evaluation paper in this issue, “Modal Contribution Coefficients in Bridge Condition Evaluation,” is by Li, Swanson, Helmicki, and Hunt. The paper describes condition evaluation work being performed on steel bridges in Ohio. Impact modal testing is combined with finite-element analysis to develop accurate stresses in these bridges for the purpose of load rating. The paper details the development of a quantitative measure of the contribution of the different modes to the overall dynamic response of a structure. This measure consists of a series of contribution coefficients that will be used to identify which modes are most critical in the process of modal testing and finite-element model calibration.

The next paper of this issue is of interest to practicing engineers working on existing railroad bridges. Al-Emrani’s “Fatigue Performance of Stringer-to-Floor-Beam Connections in Riveted Railway Bridges” experimentally examines the behavior of double-angle stringer-to-floor-beam connections in riveted railway bridges using a series of static and fatigue tests on three full-scale bridge components. The static tests revealed that the amount of end moment developed in these connections was considerable. Consequently, the fatigue tests indicated that fatigue damage might develop in these connections, however the damage was observed to have a low propagation rate and did not reduce the load-carrying function of the connections.

In “Effects of Temperature Variations on Precast, Prestressed Concrete Bridge Girders,” Barr, Stanton, and Eberhard present the findings of an investigation of observed temperature variations in precast-prestressed girders. The effects of high curing temperatures and the effect on calculated strains and cambers are discussed. The writers note that the effects on the girders can be compensated for by increasing the amount of prestressing steel, however, for highly stressed girders, this can lead to increased prestress losses and higher concrete strength requirements at release.

The next paper, “Effective Bond Length of Carbon Fiber-Reinforced Polymer Strips Bonded to Fatigued Steel Bridge I-Girders” by Nozaka, Shield, and Hajjar, describes the experimental work used to determine the effective bond length for carbon-fiber strips used to repair fatigue cracks initiating at the weld toe at the ends of a cover plated I-girder. The results of the experiment also indicated that the adhesive used had to provide relatively large amounts of ductility to redistribute the stresses during increased loading. The writers propose a simple analytical solution for the shear-strain distribution in the adhesive layer for the estimation of the effective bond length.

“Effect of Edge-Stiffening and Diaphragms on the Reliability of Bridge Girders” by Eamon and Nowak investigates the potential effects of secondary elements such as barriers, sidewalks, and diaphragms on the distribution of live load to bridge girders. The purpose of the study was to evaluate the effect of these items on the girder reliability if designed to be sufficiently attached to the bridge so as not to detach under traffic loads. Finite-element analysis of simple-span, two-lane structures was performed with the load and resistance parameters treated as random variables. The results found that the typical combinations of secondary elements have a varying influence on girder reliability, depending on secondary element stiffness and bridge geometry. The writers provide suggestions on how to account for these secondary elements and provide a uniform level of reliability.

A paper by Scollard and Barlett, “Secondary Prestressing Moments in Rehabilitated Posttensioned Bridges,” is of particular interest to practicing engineers rehabilitating posttensioned slab bridges. Typical rehabilitation of posttensioned slab bridges requires the removal and replacement of the upper surface of the deck. The removal of this portion of the deck causes changes in the primary and secondary prestressing moments and thus impact the serviceability and ultimate limit states. The paper presents an analysis procedure for computing the changes in prestressing moments caused by this rehabilitation work. The investigation looked at some common rehabilitation schemes and presents the results for each.

The final paper for this issue, “Performance of Pile-Supported Bridge Approach Slabs” by Bakeer, Shutt, Zhong, Das, and Morvant, examines the long-term performance of pile supported approach slabs used in southeastern Louisiana. A field evaluation of several slabs was performed. The results of the study indicated that the current empirical methodology used for the design of the pile-supported approach slabs yields inconsistent results in the field with the primary problem being differences in the roadway embankment design and construction, as well as subsoil conditions. The results of the study provided a new rating system for approach slabs using IRI measurements obtained with a laser profiler.

There are two discussions and a closure in this issue on “Probabilistic Strength Estimates and Reliability of Damaged Parallel Wire Cables” by S. Camo, published in the September 2003 issue of the Journal. In the first discussion, G. Baker expresses concern that the paper’s conclusions rest upon some specific assumptions regarding the ability of the wires to redevelop the broken wire’s capacity by the friction provided by the cable bands and that variations in these assumptions could significantly impact the results.

The original paper’s author, S. Camo, provides the second discussion on the paper by providing some additional information regarding the methodology detailed in the paper. The need for this came as a result of discussions on this subject at a workshop convened by the NCHRP in California.

In the closure also by S. Camo, addresses comments made in previous discussions on the original paper particularly addressing the concerns expressed in G. Baker’s discussion.

Cheng, L., Zhao, L., Karbhari, V. M., Hegemier, G. A., and Seible, F., (2005). “Assessment of a steel-free FRP-composite modular bridge system.” J. Struct. Eng., 131(1).

Jaselskis, E. J., Gao, Z., and Walters, R. C., (2005). “Improving transportation projects using laser scanning.” J. Constr. Eng. Manage., 131(1).

Museros, P., and Alarcón, E., (2005). “Influence of the second bending mode on the response of high-speed bridges at resonance.” J. Struct. Eng., 131(1).

Sirca, G. F., and Adeli, H., (2005). “Cost optimization of prestressed concrete bridges.” J. Struct. Eng., 131(1).