Papers in This Issue

This January 2012 issue of the Journal features 23 articles: 13 technical papers, 2 case studies, 4 technical notes, 2 discussions, and 2 closures. The first four papers in this issue focus on seismic aspects of bridge engineering. The manuscript “Real-Time Dynamic Substructuring Testing of a Bridge Equipped with Friction-Based Seismic Isolators” by Dion et al. presents a real-time dynamic substructuring (RTDS) test program that was carried out on a bridge structure equipped with seismic isolators with self-centering and friction energy dissipation capabilities. The structure studied also included bearing units with sliding interfaces providing additional energy-dissipation capacity. In the RTDS tests, the seismic isolator was physically tested in the laboratory using a high performance dynamic structural actuator imposing, in real-time, the displacement time histories obtained from numerical simulations being run in parallel. The integration scheme used in the test program was the Rosenbrock-W variant, and the integration was performed using the MathWorks’s Simulink and XPC target computer environment. The numerical counterpart included the bridge piers and the additional energy dissipation properties, including their nonlinear behavior. The RTDS tests were performed in the direction parallel to the length of the bridge. The effects of various ground motions and the influence of modeling assumptions, such as friction and column stiffness, were investigated. The results indicate that simple numerical modeling techniques can lead to accurate prediction of the displacement response of the bridge seismic protective systems studied. The manuscript “Lessons Learned from the Damaged Huilan Interchange in the 2008 Wenchuan Earthquake” by Sun et al. investigates damages to the Huilan Interchange Bridge during the 2008 Wenchuan earthquake in China. This study has been carried out through postearthquake investigation and identification of the cause of failure for this bridge. The bridge, constructed in 2004 in Mianzhu City, consisted of a viaduct and four horizontally circular ramp bridges with continuous box girders. Field investigations found that the seismic damage to the ramp bridges was especially heavy; one or two short piers in all but one of the ramp bridges experienced severe failure, and the box girders over the failed piers were fractured. Other piers of the ramp bridges suffered minor to moderate damage, including concrete cover spalling, concrete cracking, and slippage damage of the rubber bearings. The viaduct suffered only slight damage, including slippage damage in rubber bearings and pounding damage of the superstructure. The seismic performance of the bridge was evaluated by finite-element modeling (FEM) and compared with field observations. It was found that the bearing on top of the shortest pier was damaged first. Then, the seismic action became concentrated on the next shortest pier, which had the largest flexural stiffness. This pier yielded in flexure and eventually failed in flexure-shear mode. The next two papers are companion papers focusing on structural fuses and bi-steel columns. The manuscript “Bridge Piers with Structural Fuses and Bi-Steel Columns. I: Experimental Testing” by El-Bahey and Bruneau proposes structural fuses as part of a multicolumn accelerated bridge construction (ABC) pier concept. These fuses are easily replaceable sacrificial elements for dissipating seismic energy while preventing damage to the gravity load-resisting structural system. Different types of structural fuses have been investigated in this study to compare the effect of each on ABC bridge bents. The piers of a three-span continuous bridge prototype having two twin-column pier bents were designed using double composite rectangular columns and structural fuses. Two corresponding $2/3$ scale models were developed and were subjected to cyclic quasi-static tests. For the first specimen, steel plate shear links (SPSLs) were installed between the columns as a series of structural fuses. Testing was performed, first up to a drift corresponding to the onset of column yielding to investigate the effectiveness of adding the fuses in dissipating the seismic energy, then up to failure of the composite columns. The second specimen has buckling restrained braces (BRBs) as a series of structural fuses between the columns. The BRBs were then removed and cyclic testing of the composite bent continued until failure of the columns. Both specimens exhibited stable hysteretic behavior, with structural fuses increasing both stiffness and strength of the bent. In the manuscript “Bridge Piers with Structural Fuses and Bi-Steel Columns. II: Analytical Investigation,” El-Bahey and Bruneau present the results of an analytical investigation conducted to replicate the experimentally obtained behavior and better understand behavior of the proposed structural fuse concept for bridges presented in the companion paper. First, an SPSL proposed as a new type of structural fuse is described. FEMs are developed using the finite-element software package ABAQUS/explicit to validate the proposed SPSL concept. It is found that the simple numerical equations can well represent the expected strengths and stiffnesses of the fuse systems. The results obtained from the ABAQUS model captured well the global behavior of the system and provided valuable insight into individual fuse behavior.

Next, two papers focus on fatigue behavior of bridges. The manuscript “Assessment of Slender Long-Span Bridges: Reliability Approach” by Wu et al. investigates a reliability-based fatigue assessment model that can rationally consider combined load effects from wind and traffic and associated uncertainties for an accurate estimate of reliability for fatigue. A scenario-based deterministic fatigue analysis model is developed. In this model, a typical year is categorized into several representative scenarios of traffic and wind conditions. After identifying the duration for each representative scenario in a typical year, a cumulative yearly fatigue damage factor can be predicted by superposing the cumulative hourly damage factors for all representative scenarios. Based on the scenario-based deterministic analytical model, the framework of the reliability-based fatigue damage assessment for a slender long-span bridge is further developed and is illustrated for a prototype bridge. The manuscript “Probabilistic Fatigue Life Estimation of Steel Bridges by Using a Bilinear S-N Approach” by Kwon et al. focuses on estimating fatigue life below the constant amplitude fatigue threshold (CAFT) of steel bridges by using a probabilistic approach based on bilinear stress life (i.e., S-N). The current AASHTO S-N approach is based on a single S-N line for prediction of fatigue life. However, due to the variation of actual applied live-load stress cycles, this approach very often results in severe underestimation of the useful life of structures. It implies that fatigue damage in respective structural steel details may be overpredicted. To improve fatigue life estimation, a bilinear S-N approach is integrated into a probabilistic framework that can model the uncertainties associated with the fatigue deterioration process. In this approach, the equivalent stress range is computed by considering two S-N slopes and several probability density functions associated with stress ranges. These probabilistic functions are determined on the basis of stress-range bin histograms from long-term monitoring. The proposed approach is illustrated on an existing bridge that is expected to experience finite fatigue life.

The next two manuscripts in this issue focus on culverts. The manuscript “Load-Rating Procedures and Performance Evaluation of Metal Culverts” by Yeau and Sezen investigates the effectiveness of current load-rating procedures for corrugated metal culverts. Recommendations are made to improve the analysis and evaluation procedures for corrugated metal culverts. The proposed load-rating procedure is based on an extensive review of load-rating procedures and design practices, experimental data, and theoretical investigations. The proposed method does not include a rating factor for cover depth. However, the design cover depth is required to be checked during the initial design stage to ensure structural stability. New capacity reduction factors are introduced for culvert wall and seam, which require different appraisals for wall and seam during annual inspections. The effect of external live loads is not included in the proposed load-rating procedure for deep culverts and for culverts subjected to low live load stresses. Field data from 39 in-service culverts show that the proposed load-rating procedure is effective in evaluating the existing condition of culverts. The manuscript “Testing and Analysis of a Deep-Corrugated Large-Span Box Culvert prior to Burial” by Brachman et al. investigates the use of deep-corrugated steel culverts (corrugation wavelength 400 mm and amplitude 150 mm) as an alternative to short-span bridges. A large-scale laboratory test has been conducted on a 10-m-span structure responding to a pair of vertical loads placed along the crown before burial. This test has been modeled by using two different approaches. The first three-dimensional finite-element calculations were based on explicit modeling of the corrugated structure. The second calculations were based on orthotropic shell theory. Comparisons are then made between the two sets of calculations and measured values of displacement and circumferential strain, and moment and thrust calculated from measured strain. The corrugated analysis produced estimates of displacement at the center of the structure within 0.2% of measured values, whereas the orthotropic shell analysis yielded an error of 4%. The corrugated analysis provided strain values much closer to those that were measured. Moment and thrust values from the corrugated analysis were within 3% and 2% of the experimental values, respectively, whereas values from the orthotropic analysis erred by much higher amounts, particularly in the vicinity of loading points where the orthotropic analysis cannot model local effects.

The next two papers in this issue focus on bridge deck systems. The manuscript “Numerical Evaluation of the Long-Term Behavior of Precast Continuous Bridge Decks” by Sousa et al. presents a monitoring and analysis strategy developed to assess the long-term variation of strains and stresses in precast continuous bridges. The numerical analysis was validated by comparison with the results observed in a real bridge. The consequences of carrying out simplified analyses based on limited information about the concrete properties and the construction sequence have also been evaluated. The manuscript “Experimental Evaluation of Aluminum Bridge Deck System” by Saleem et al. evaluates an alternative lightweight extruded aluminum deck system as well as weight and thickness limits for moveable bridge decks. These aluminum deck panels with their tongue-and-groove connections have previously been used in Europe (mainly Sweden). A detailed experimental evaluation of the aluminum deck system has been carried out, including static and fatigue load testing on the deck panels, as well as ancillary tests on the connections with the girders. Based on the in-depth experimental evaluation and the subsequent FEM and predictions, the extruded aluminum deck is shown to be a feasible alternative to the open-grid steel deck and is ready for implementation on movable bridges as well as bridges that require a lightweight deck.

The remaining three technical papers in this issue focus on diverse aspects of bridge engineering. The manuscript “Concrete-Filled Steel Tubular Tied Arch Bridge System: Application to Columbus Viaduct” by Morcous et al. presents the design and construction challenges pertinent to a novel concrete-filled steel tubular tied arch system that was first introduced in the Ravenna Viaduct (53 m) and applied later to the Columbus Viaduct (79 m). The main structural components of the Columbus Viaduct are described in detail, and the advantages of the system are summarized. The detailed analysis of the system at different construction stages and design checks of main components and connections under various loading conditions are discussed. Experimental investigations conducted on concrete-filled steel tubular arch and tie specimens to validate their theoretical capacities are demonstrated. The three-dimensional nonlinear FEM developed to analyze the tie-to-arch connection and to evaluate the lateral stability of arches is presented. The manuscript “Optimal Resilience- and Cost-Based Postdisaster Intervention Prioritization for Bridges along a Highway Segment” by Bocchini and Frangopol presents a general framework for the optimal resilience and cost-based prioritization of interventions on bridges distributed along a highway connection between two cities that have experienced a disruptive natural or man-made event. Given the damage levels after the extreme event and the bridge characteristics, the proposed computational procedure finds the best intervention schedules, defined as starting time and progress pace of the restoration. The possible intervention schedules are considered optimal when they maximize the resilience of the highway segment and minimize the cost. Because the two objectives are conflicting, the procedure uses genetic algorithms to automatically generate a Pareto front of optimal solutions. Numerical examples are presented and discussed. The manuscript “Instrumentation, Nondestructive Testing, and FEM Updating for Bridge Evaluation Using Strain Measurements” by Sanayei et al. presents the development of a baseline FEM for bridge management and its calibration using nondestructive test data. The model-calibration technique was evaluated on the Vernon Avenue Bridge over the Ware River in Barre, Massachusetts. This newly constructed bridge was instrumented throughout its construction phases in preparation for a static truck load test that was performed before the bridge opening. The strain data collected during the load test was used to calibrate a detailed baseline FEM in an effort to represent the system behavior of the bridge. Once the model was calibrated, it was used to calculate load-rating factors.

The next two papers in this issue are case studies. The manuscript “Case Study of Strategies for Seismic Rehabilitation of Reinforced Concrete Multicolumn Bridge Bents” by Pantelides and Fitzsimmons presents a case study on a comparison between different seismic rehabilitation approaches for four reinforced concrete multicolumn bridge bents typical of older bridges not designed according to current seismic codes. The types of retrofits included connecting the piles to the pile caps with high-strength prestressing steel bars, widening an existing strut beam connecting the pile caps, construction of a new reinforced concrete grade beam overlay to connect the pile caps, and carbon fiber reinforced polymer (CFRP) composite jackets for strengthening the columns and cap beam-column joints. Hysteresis curves from in situ experiments in which a lateral quasi-static cyclic load was applied at the cap beam has been used in the analysis. A comparison of the capacity of the four bents to the demand of several earthquake records including historical and NEHRP design earthquakes is developed. The cost of seismic rehabilitation of the four bridge bents is presented along with the peak maximum lateral load and maximum displacement achieved in the experiments. The cost of the seismic rehabilitation is related to the performance of each bridge bent. The bridge bent with the lowest level of intervention had the lowest cost and met the displacement and base shear demands for the 10% in 50 years NEHRP design earthquake; the bridge bent with the highest level of intervention had the highest cost and met the displacement and base shear demands for the 2% in 50 years NEHRP design earthquake. The manuscript “Assessment of Simplified Linear Dynamic Analysis of a Multispan Skew Bridge on Steel-Reinforced Elastomeric Bearings” by Whelan and Janoyan presents modal parameter estimates obtained from a large-scale field deployment of accelerometers supported under a wireless sensor network. Through output-only system identification, the natural frequencies, damping ratios, and mode shapes are extracted for the first 20 structural modes. Linear dynamic analysis of the bridge through three-dimensional finite-element analysis is then performed to provide a comparison between the response estimate predicted under the minimum requirements of multimode spectral analysis dictated by the AASHTO design specifications and the in-service dynamic response. Linear elastic bearing stiffness in the compressive, shear, and flexural states is estimated using independent design specifications set forth by AASHTO and Standards Australia as well as modeled with idealized fixity. The case study concludes that linear dynamic analysis provides a well-correlated, yet conservative estimate of multimodal displacement for bridges supported by steel-reinforced elastomeric bearings when bearing stiffness is defined using either design specification.

In the manuscript “Practical Formula for Cable Tension Estimation by Vibration Method” by Fang and Wang, the authors propose a practical formula for estimating the cable tension in a simple explicit form, in which the bending stiffness of the cable is included, the sag effect is neglected for simplicity by using the frequencies relative to antisymmetric or higher vibration modes of the cable. The capability of this formulation is verified through comparison with available experimental results and finite-element solutions, which indicates that the formula developed in this paper is sufficiently accurate and can be conveniently applied to field measurement for cable-supported bridge systems. The manuscript “Field Test and FEM of a Skewed Railroad Truss Bridge” by Diaz-Alvarez et al. focuses on the effects of skew angle on the geometry and design of a bridge. Skew angles greater than 20° affect bending moment and shear force in an exterior beam. The U.S. Army Engineer Research and Development Center (ERDC) performed a full-scale load test on a skewed railroad steel truss bridge at Fort Leonard Wood, Missouri, in July 2007. The superstructure of the bridge was instrumented with 42 reusable strain transducers to accurately measure the structure’s response to a 260-kip train engine. Analyses were carried out to determine the effect of the skew angle in that response. A three-dimensional FEM was developed from the data collected during the load test. The measured internal axial forces compared satisfactorily with the results from the FEM analysis. After calibration of the model, results indicated that the skew angle decreased the internal axial forces by approximately 16%, which is comparable to current design practice. The manuscript “LCC Analyses of a New Steel for Bridges” by Okasha et al. presents computations, results, and conclusions of an analytical investigation for comparing the life-cycle cost (LCC) of a steel bridge component made of a new maintenance-free steel and the LCC of the same steel bridge component made of conventional painted carbon steel with maintenance (repainting). An approach for the LCC analysis is presented both deterministically, in which different painting scenarios are considered, and probabilistically, in which the uncertainties in the input variables are properly considered. Under reasonable cost assumptions, it is demonstrated that the new steel, although initially more expensive, is indeed cost-effective after approximately 15 years. The life-cycle cost-effectiveness of the new steel increases over the service life of the bridge component. The manuscript “Rational Alternative to Positive Discovery of Pile-Supported Bridges with Unknown Foundation Depth” by Sayed et al. presents an assessment of the predictive capability of various methods currently in use to determine the embedment of bridges with unknown foundation depth. The methods discussed include sonic echo method (or pile integrity tester) as a nondestructive testing (NDT), inference (IM) and/or back-calculation (BC) [i.e., reverse engineering (RE)], and static/back-calculation (S/BC). The well-documented case histories presented in the paper illustrate the usefulness of the S/BC method in determining the embedment of unknown foundations. The S/BC can also be used to assess/validate NDT results and embedment estimates made by IM and/or BC (i.e., RE) approaches. For high priority unknown foundation bridges, the S/BC reasonable minimum embedment and the embedment required for stability considering the scour can be used to plan and efficiently implement any future NDT for these bridges. It can significantly reduce the cost of treating unknown foundation bridges by optimizing the use of NDT, if warranted. The three case histories presented in the paper also suggest that, in general, the sonic echo (i.e., pile integrity tester)/NDT method tends to be conservative, whereas the IM and/or BC (i.e., RE) methods, on the other hand, tend to be unconservative.

This issue of the Journal has two discussions and two closures. Discussers Bakht et al. have presented a very detailed discussion of the published article “Operational Requirements for Long-Span Bridges under Strong Wind Events” by Cheung and Chan from the March 2010 issue. Cheung and Chan have provided a closure by thanking the discussers and providing their rationale to the discussers’ comments. Discusser Abrahams has presented a discussion on “Steel Girder Stability during Bridge Erection: AASHTO LRFD Check on $L/b$ Ratios” by Hastings et al. from the December 2010 issue. Hastings et al. have provided a closure by thanking the discussers and providing their rationale to the discusser’s comments.