Editor’s Note

The first five papers in the May 2010 issue of the Journal of Bridge Engineering are focused on the behavior of bridges subject to various types of dynamic loads, such as traffic, wind, earthquakes, etc. “Dynamic Performance Simulation of Long-Span Bridge under Combined Loads of Stochastic Traffic and Wind” by Chen and Wu presents a new “semideterministic” bridge dynamic analytical model that considers dynamic interactions between bridge, wind, and stochastic “real” traffic by integrating the equivalent dynamic wheel load (EDWL) approach and the cellular automaton (CA) traffic flow simulation. Using this approach, statistical dynamical behavior of long-span bridges can be predicted with a more realistic and adaptive consideration of combined loads of traffic and wind. In addition to slender long-span bridges, which are sensitive to wind, this model can also be used for other conventional long-span bridges as well as roadway pavement to achieve more realistic understanding of the structural performance under probabilistic traffic and dynamic interactions.

The paper “Large-Bar Connection for Precast Bridge Bents in Seismic Regions” by Pang, Eberhard, and Stanton presents a new beam-to-column connection made with a small number of large column bars, which are grouted into large corrugated metal-ducts embedded in the cap-beam, for a rapid assembly of precast concrete bridge bents in regions of high seismicity. The authors have evaluated the seismic performance of the proposed connection by lateral-load tests on three manifestations of the connection, as well as on a comparable cast-in-place connection and have demonstrated that the force-displacement response and damage progression in the precast connection are similar to those of typical cast-in-place concrete connections.

The paper “Modeling Residual Displacements of Concrete Bridge Columns under Earthquake Loads Using Fiber Elements” by Lee and Billington investigates the inability of nonlinear dynamic analysis methods with fiber element models in predicting postearthquake residual displacements in bridges. The authors have observed that a certain type of pinching present in the hysteretic shape responsible for a poor residual displacement simulation in the SDOF models is also present in fiber element models. The authors have implemented a modified concrete constitutive model in the fiber element analysis that incorporates changes to reloading behavior when moving from high tensile strain back to compression for an improved simulation of residual displacements.

In “Behavior of Bridge Asphalt Plug Joints under Thermal and Traffic Loads,” Park, El-Tawil, Park, and Naaman investigate the behavior of a typical asphalt plug joint (APJ) subjected to thermal and traffic loads through a series of finite-element analyses employing a temperature-dependent viscoplastic material model with previously published test data. Results show the behavior of APJ response under traffic and thermal loadings and provide new, fundamental information that can be used to improve the durability of APJs. For example, the simulation results suggest that intentionally debonding the interface between the gap plate and the APJ is a practical and low cost solution to mitigate the risk of premature APJ failure.

“Aerostatic Reliability Analysis of Long-Span Bridges” by Su, Luo, and Yun proposes the response surface Monte-Carlo method (RSMCM) for the reliability analysis of aerostatic response and aerostatic stability for different types of long-span bridges by taking into consideration nonlinear effects due to geometric nonlinearity and deformation-dependent aerostatic loads. The authors have applied the proposed approach to the reliability analysis of aerostatic response and aerostatic stability of the Hong Kong Ting Kau Bridge to demonstrate the effectiveness of the method.

The remaining seven papers are in diverse areas of bridge engineering. In “Dynamic Simulation of the Maglev Vehicle/Guideway System,” Ren, Romeijn, and Klap have developed a numerical model consisting of models of guideway and maglev vehicle to investigate the dynamic characteristics of the maglev system. The authors have compared the numerical results with the corresponding values given by MSB-AG-Fahrweg and have observed the vehicle model with sixteen electromagnetic forces to be the most appropriate simplification. The guideway irregularity model has been observed to have a greater influence on the acceleration of the carriage body rather than those on the guideway displacement.

“Rotation Requirements for Moment Redistribution in Steel Bridge I-Girders” by McConnell and Barth analytically investigates ductility requirements specifically applicable to AASHTO moment redistribution procedures that are valid for all I-girders and propose empirical equations predicting the amount of rotation required as a function of the intended level of moment redistribution as well as the material properties and span configuration of the girder. These results can be used for reducing the overly conservative nature of existing AASHTO moment redistribution specifications.

“Fatigue and Strength Evaluation of Two Glass Fiber-Reinforced Polymer Bridge Decks” by Brown and Berman investigates fatigue and strength testing of two types of GFRP decks being considered for use in the retrofit of an aging steel arch bridge in Snohomish County, Washington, where a roadway expansion is necessary and it is desirable to minimize the improvements to the arch superstructure. Results from the fatigue testing indicate less than 12% degradation in the stiffness of both deck types over the duration of loading, permanent deck displacement during fatigue loading in both deck types, a poor fatigue performance of detailing in one of the decks, and degradation of composite behavior between the deck and girders during fatigue loading.

In “Validated Simulation Models for Lateral Response of Bridge Abutments with Typical Backfills,” Shamsabadi, Khalili-Tehrani, Stewart, and Taciroglu present numerical simulation models that are validated using data from recent experiments on the lateral response of typical abutment systems. These tests involve well-compacted clayey silt and silty sand backfill materials. Through parametric studies on the validated log-spiral hyperbolic model, the authors develop equations for the lateral load-displacement backbone curves for abutments of varying height for the two aforementioned backfill types. The equations describe a hyperbolic relationship between lateral load per unit width of the abutment wall and the wall deflection and are amendable to practical application in seismic response simulations of bridge systems.

“Inclusion of Crawl Tests and Long-Term Health Monitoring in Bridge Serviceability Analysis” by Orcesi and Frangopol presents a methodology for lifetime serviceability analysis of existing steel girder bridges including crawl tests and long-term monitoring information. The paper considers the case where the initial goal of monitoring is to provide data for a fatigue analysis of some bridge components to perform a structural reliability analysis in different sections that are critical, considering serviceability of the bridge. An application of the proposed approach is demonstrated by considering the I-39 Northbound Bridge over the Wisconsin River in Wisconsin monitored by the ATLSS Center at Lehigh University.

“Improved Longitudinal Joint Details in Decked Bulb Tees for Accelerated Bridge Construction: Concept Development” by Li, Ma, Griffey, and Oesterle presents an investigation of improved continuous longitudinal joint details for decked precast prestressed concrete-girder bridge systems for a rapid construction along with improved structural performance and durability. This paper presents the results of a study assessing potential alternate joint details based on constructability, followed by testing of seven reinforced-concrete beam specimens connected with either lapped headed reinforcement or lapped welded wire reinforcement (WWR) along with a specimen reinforced by continuous bars for comparison. Evaluation of test results based on flexural capacity, curvature at failure, cracking, deflection, and steel strain indicates that a headed bar detail with a $152\mathrm{mm}$ $\left(6\mathrm{in.}\right)$ lap length is appropriate for replacing current welded steel connector detail.

In “Proposal of an Integrated Index for Prioritization of Bridge Maintenance,” Valenzuela, de Solminihac, and Echaveguren propose a need-based framework for developing an integrated bridge index (IBI) as an aid for prioritization and decisions stakeholders make on maintenance and rehabilitation of bridges. The index weights the structure distresses, hydraulic vulnerability, seismic risk, and strategic importance of the bridge, and has been calibrated using visual inspection, survey to experts, and regression analysis. The authors demonstrated the proposed approach through applications to six bridges in Chile.

Finally, this issue of the Journal has two discussions and one closure. Qin and He present a discussion of “Bridge Reliability Assessment Based on Monitoring” by Frangopol, Strauss, and Kim, originally published in the May/June 2008 issue. They point out that the localizations of sensors of monitoring system on the Lehigh River Bridge SR-33 considered by the authors may not sense damages or cracks that generally occur at the ends of a member. They also question the calculation of reliability indexes of the steel upper chords of the bridge by assuming perfect condition of shear studs, concrete deck, and stringers, since stresses in the steel upper chords of the trusses may increase if the shear studs or concrete deck fail, leading to reductions in the reliability indexes of the steel upper chords.

Chen and Tu have presented a discussion on “Static Behavior and Theoretical Model of Stud Shear Connectors” by Xie, Ding, Wang, and Luo, published in November/December 2008 issue of the Journal. They discuss several issues related to governing failure of the shear connections, load-slip curves, and influence of $H∕d$ . In the closure to the discussion by Chen and Tu, the authors Xie, Ding, Wang, and Luo thank the discussers and provide a detailed answer to their concerns.