Editor’s Note

The January 2011 issue of the ASCE Journal of Bridge Engineering begins with four papers on various aspects of reinforced concrete decks. “Compound Shear-Flexural Capacity of Reinforced Concrete–Topped Precast Prestressed Bridge Decks” by Mander et al. discusses failure of concrete bridge decks commonly consisting of stay-in-place (SIP) precast panels seated on precast concrete beams and topped with cast-in-place (CIP) reinforced concrete. Delamination is observed to occur between the CIP concrete and SIP panels because of a compound shear-flexure mechanism when monotonically increasing patch loads are applied. The authors propose an additive model of flexural yield line failure in the lower SIP precast prestressed panels, and punching shear in the upper CIP reinforced concrete portion of the deck system. Comparison of analysis results to those of full-scale experiments of a tandem wheel load straddling adjacent SIP panels, and a trailing wheel load on a single panel shows that load capacities by the proposed compound shear-flexure failure mechanism are within 2% of the experimentally observed loads. It is observed that individual estimates by yield line and punching theories are significantly different from observed ones.

“Modified Yield Line Theory for Full-Depth Precast Concrete Bridge Deck Overhang Panels” by Mander et al. discusses full-depth precast overhang bridge deck panels in concrete bridge deck construction. The authors present a modified yield line theory that accounts for the development length of the mild steel reinforcement to reach yield strength. Failure of the full-depth panels is influenced by the presence of the partial-depth transverse panel-to-panel seam. When applying a load on the edge of the seam, the loaded panel fails under flexure, while the seam fails in shear. Through the use of the modified yield line theory coupled with a panel-to-panel shear interaction, analytical predictions are found to be accurate within 1–6% of experimental results.

“Full-Scale Test of Continuity Diaphragms in Skewed Concrete Bridge Girders” by Saber and Alaywan presents results of field verification of the effectiveness of continuity diaphragms for skewed, continuous, prestressed concrete girder bridges, based on full-scale tests of a prestressed concrete bridge with continuity diaphragms and a skewed angle of 48°, by the Louisiana Department of Transportation and Development, and the Federal Highway Administration. The findings indicate that the effects of the continuity diaphragms are negligible and they can be eliminated. The superstructure of the bridge could be designed with link slab, so that the bridge deck can provide continuity over supports, improvement in the ride quality, increase in structural redundancy, and reduction in expansion joint installation and maintenance costs.

“Time-Dependent Reliability of PSC Box-Girder Bridge Considering Creep, Shrinkage, and Corrosion” by Guo et al. investigates time-dependent reliability assessment for a composite prestressed concrete (PSC) box-girder bridge exposed to a chloride environment by applying CEB-FIP model for creep and shrinkage, based on finite element analysis in conjunction with probabilistic considerations. It is shown that concrete creep and shrinkage are dominant during the early stages of bridge structure deterioration. This is accompanied by a decrease in reliability owing to the combined action of creep, shrinkage, and corrosion. The reliability indices for the serviceability and the tendon yielding limit state fall below the target levels prior to the expected service life, resulting in early maintenance and/or repairs.

The next two papers discuss issues related to deterioration and bridge management. “Optimization of Maintenance Strategies for the Management of the National Bridge Stock in France” by Orcesi and Cremona discusses maintenance and repair activities crucial for preventing deterioration of highway bridges in France by optimizing the allocation of maintenance funds. The objective of this study is to determine global financial resources needed to satisfy the constraints on the quality indicators over the next $15\text{years}$ , based on Markov chains fitted to condition data collection. By including prediction models in the cost analysis, different maintenance strategies are evaluated. Applied to the French national bridge stock, the procedure shows that a slight increase in the annual budget is required to fulfill the asset performance requirements fixed by the Roads Directorate.

In “Reliability of Bridge Decks in Wisconsin,” authors Tabatabai et al. focus on identifying the most suitable reliability model for bridge decks in Wisconsin, and utilizing that model for detailed analyses of bridge deck reliability and failure rates. Using 2005 National Bridge Inventory (NBI) data for the state of Wisconsin, they investigate hypertabastic, Weibull, log logistic, and lognormal distributions. The end of service life is defined as the age of the deck when rehabilitation or replacement is required (defined as a deck rating between 4 and 5). The effects on NBI deck rating of Average Daily Traffic (ADT), type of bridge superstructure (steel or concrete), and the deck surface area were considered. Based on the Akaike Information Criteria, the Hypertabastic Accelerated Failure Time model has been selected as the most appropriate model for this study. Results show that deck area, type of superstructure, and ADT are all important factors affecting the reliability of bridge decks in Wisconsin.

The next eight papers discuss various issues related to dynamic loads and other effects on bridges, e.g., seismic, blast, impact, etc. “Experimental Investigation of Seismically Resistant Bridge Piers under Blast Loading” by Fujikura and Bruneau reports the findings of research examining the blast resistance of bridge piers, that are designed in accordance with current knowledge and specifications to ensure ductile seismic performance. Blast testing was conducted on $1∕4$ -scale ductile reinforced concrete (RC) columns, and non-ductile RC columns retrofitted with steel jacketing. Both seismically designed RC and steel jacketed RC columns did not exhibit a ductile behavior under blast loading and failed in shear at their base, rather than in flexural yielding. A moment-direct shear interaction model has been proposed to account for the reduction of direct shear resistance on cross sections, when large moments are simultaneously applied.

“Ductility Evaluation of Concrete-Encased Steel Bridge Piers Subjected to Lateral Cyclic Loading” by Naito et al. discusses an experimental and analytical study to investigate the ductility of concrete-encased steel piers, referred to as “steel reinforced concrete (SRC) construction.” Based on the cyclic lateral loading tests of SRC column specimens, restorable limit state is defined as the point where concrete cover spalling occurs (equivalent to longitudinal bar buckling). Likewise, ultimate limit state is defined as the point where flange buckling of the H-shaped steel occurs. The authors estimate the lateral displacement capacity at both these limit states by integrating the curvature distribution of the column. The curvature distribution was calculated based on the buckling analysis of the longitudinal bar restrained by a concrete cover and transverse reinforcement, and of the steel flange encased in concrete. Comparison between computer and experimental results, including those available in literature, shows that the proposed method can appropriately estimate the lateral displacement at restorable and ultimate limit states, and it can accurately evaluate the buckling characteristics of the longitudinal bar and steel flange components of SRC column specimens.

“Bridge Seismic Retrofitting Practices in the Central and Southeastern United States” by Wright et al. conducts a detailed review of the seismic hazard, inventory, bridge vulnerability, and bridge retrofit practices in the Central and Southeastern United States (CSUS). Based on the analysis of the bridge inventory in the CSUS, it is observed that over 12,927 bridges (12.6%) are exposed to 7% PE in $75\text{years}$ with peak ground acceleration (PGA) greater than $0.20\mathrm{g}$ , and nearly 3.5% of bridges in the CSUS have a 7% PE in $75\text{years}$ with a PGA greater than $0.50\mathrm{g}$ . The review of retrofit practices in the region indicates that the most common retrofit approaches in the CSUS include the use of restrainer cables, isolation bearings, column jacketing, shear keys, and seat extenders. The paper presents an overview of the common approaches and details used for the retrofit measures mentioned above. This paper will be useful to bridge engineers in Central and Southeastern United States.

“Efficient Longitudinal Seismic Fragility Assessment of a Multispan Continuous Steel Bridge on Liquefiable Soils” by Aygün et al. presents a computationally economical yet adequate approach, that links nonlinear finite element models of a three-dimensional bridge system with a two-dimensional soil domain and associated one-dimensional set of p-y springs into a coupled bridge-soil-foundation (CBSF) system. A multispan continuous steel girder bridge, typical of the central and eastern United States, along with heterogeneous liquefiable soil profiles is used within a statistical sampling scheme to illustrate the effects of soil failure and uncertainty propagation on the fragility of CBSF system components. In general, the fragility of rocker bearings, piles, embankment soil, and the probability of unseating increases with liquefaction, while that of commonly monitored components, such as columns, depends on the type of soil overlying the liquefiable sands. This component response dependence on soil failure supports the use of reliability assessment frameworks that are efficient for regional applications, by relying on simplified but accepted geotechnical methods to capture complex soil liquefaction effects.

“Experimental Assessment of Dynamic Responses Induced in Concrete Bridges by Permit Vehicles” by Szurgott et al. presents results from experimental testing of three permit vehicles. Selected heavy vehicles that require permits from state Departments of Transportation (DOTs), include two tractor-trailers systems and a midsize crane. The vehicles are experimentally tested on popular existing speed bumps and on a representative highway bridge. The selected bridge is a reinforced concrete structure constructed in 1999, and is located on US-90 in northwest Florida. The bridge approach depression, combined with a distinct joint gap between the asphalt pavement and the concrete deck, trigger significant dynamic responses of the vehicle-bridge system. Similar dynamic vibrations are observed and recorded when the permit vehicles are driven over the speed bumps. Time histories of relative displacements, accelerations, and strains for select locations on the vehicle-bridge system are recorded. The analysis of experimental data allows for assessment of actual dynamic interaction between the vehicles and the speed bumps, as well as dynamic load allowance factors for the selected bridge.

“Dynamic Demand of Bridge Structure Subjected to Vessel Impact Using Simplified Interaction Model” by Fan et al. presents an alternate simplified interaction model to evaluate the dynamic demand of bridge structure under vessel impact. In this method, ship motion is regarded as the motion of a single degree of freedom, and ship-bow is modeled by a nonlinear spring element (only compression) connected to bridge structure. Results of the study show that the dynamic responses of bridge structures using the simplified interaction models are in good agreement with the general-purpose collision analyses, improving computational efficiency drastically.

“Study of Verrazano-Narrows Bridge Movements during a New York City Marathon” by Setareh presents details on the study of human-induced vibration of the Verrazano-Narrows Bridge. From the analysis of recorded data, excited local mode of the bridge deck within the range of the runners’ step frequency is identified. In addition, the computed bridge global response using observed runner density and estimated weight shows excellent agreement with the bridge measured response. The bridge deck vibration level during the marathon is found to be within the acceptable range for the runners.

“Modeling of Jointed Connections in Segmental Bridges” by Veletzos and Restrepo presents a segment joint modeling approach for accurately estimating the seismic response of superstructure segment joints to input ground motions. The approach is a compromise between the detailed and computationally intensive continuum mechanics based finite element approach and a simple approach that models the joints with truss elements. The approach considers the nonlinear tendon-grout slip response and is validated with data from large scale experiments. Numerous modeling sensitivity studies are performed, and recommendations for implementation in full scale models are presented.

The last two papers present research on a composite ultrahigh-performance fiber-reinforced concrete (UHPFRC)-carbon fibers-timber bridge concept, and geometric design of bridge asphalt plug joints, respectively. “Experimental Validation of a $10\text{-}\mathrm{m}$ -Span Composite UHPFRC–Carbon Fibers–Timber Bridge Concept” by Mekki and Toutlemonde presents the outcome of an experimental study of a new structure for a $10\text{-}\mathrm{m}$ -span bridge deck, which takes into account the range of possibilities offered by new and high-strength materials, along with the advantages of a traditional environmentally-friendly material. This $10\text{-}\mathrm{m}$ -span element is formed by wooden beams braced at their ends on supports, a thin ( $7\text{-}\mathrm{cm}$ thick) upper slab made of precast UHPFRC, and FRP at the lower chord of these beams. The test program is aimed at identifying the major critical aspects involved in producing an initial estimate of safety margins, as well as validations of the design process and its underlying assumptions. Under the first loading configuration derived from live traffic loads, both the transverse and local bendings of the thin UHPFRC slab are activated and confirmed by 3D finite element (FE) computation. The second loading configuration corresponds to pure global longitudinal bending, with the bearing capacity being monitored up to the theoretical ultimate limit state (ULS) loading and then beyond to experimental failure. Critical mechanisms and safety factors are been identified. Though concept feasibility has been demonstrated, some aspects need further optimization to obtain greater ductility and safer control over failure modes and occurrences.

“Improved Geometric Design of Bridge Asphalt Plug Joints” by Park et al. presents detailed finite element simulations to develop a better understanding of the parameters that influence asphalt plug joints (APJ) response under traffic and thermal loading conditions. The computational model employs a time- and temperature-dependent viscoplastic material model, and is validated by comparing model results to previously published experimental data. The key parameters investigated are gap plate width, gap plate thickness, gap plate edge geometry and geometry of the interface between the pavement and APJ. The resulting information is synthesized into a proposed alternative APJ design that minimizes local demands deemed responsible for the observed early failures.

This issue of the Journal has two technical notes. “Experimental Dynamic Response of a Short-Span Composite Bridge to Military Vehicles” by Robinson and Kosmatka describes the field testing of a newly developed light-weight fiber reinforced polymer (FRP) bridging system to meet the US military’s needs. The study investigates dynamic impact loads of track and wheel vehicles at different crossing speeds to increase understanding of appropriate impact factors used in design. It is found that the impact loads for the bridge treadways are most sensitive to vehicle crossing speed and vehicle type (wheel versus track and axle spacing) with observed impact factors as high as 1.71.

“Analytical Models and Guidelines for the Ductility Enhancement of Circular Reinforced Concrete Single-Column Bents Using Fiber-Reinforced Polymers” by Abela and Attard discusses the target displacement ductility requirements for circular reinforced concrete (RC) single-column bridge bents, using a proposed multifailure mode algorithm to determine the required thickness of fiber-reinforced polymer (FRP) wraps. The procedure is developed using two in-house computer algorithms, PACCC (Plastic Analysis of Circular Concrete Columns) and PACCC-FRP, to generate a moment-curvature analysis using circular segment slices, and subsequent failure mode predictions in single-column bents for both FRP-wrapped and unwrapped circular RC sections. The results of the study shows good comparison to published experimental tests at the ultimate force-deflection states of RC sections and against three commercial “software test beds.” The study uses PACCC-FRP to show that single-columns experiencing brittle failure may be retrofitted with FRP wraps to increase the displacement ductility and satisfy target ductility values within the Ductility Wrap Envelope (DWE), or wrap-saturation level established in the study.