Journal of Bridge Engineering

The design of bridges based on current seismic design codes is prescriptive and targets a uniform seismic hazard level rather than a uniform risk (i.e., loss). This paper puts forward an applied method for reliable performance-based seismic design of bridges founded on a design philosophy in which tolerable seismic loss is incorporated in the design decision process up front. The proposed technique is based on a few simple design-aid graphs that are developed using a full Monte Carlo probabilistic simulation over a Pacific Earthquake Engineering Research Center (PEER) Probabilistic-Based Seismic Assessment (PBSA) approach while considering the correlation between demands in different components to estimate bridge repair cost ratios (RCRs) at various levels of column drift ratio (CDR). A Bayesian updating method is used to develop the probability distribution of CDRs given RCR. In this paper, the method is exercised for the design of a two-span Caltrans ordinary bridge. Various design parameters, such as column diameter, column height-to-depth ratio, longitudinal reinforcement ratio, and span length, are included in the design process. The bridge probability of collapse and the probability of exceeding a RCR are estimated for various design-parameter configurations. The proposed bridge seismic design method can serve as the basis for the design of bridges for uniform risk.

The accuracy of bridge system safety evaluations and reliability assessments obtained through refined structural analysis procedures depends on the proper modeling of traffic load effects. While the live-load models specified in AASHTO procedures were calibrated for use in combination with approximate analysis methods and load-distribution factors commonly used in the United States, these existing models may not produce accurate results when used in association with advanced finite-element analyses of bridge structures. This paper proposes a procedure for calibrating appropriate live-load models that can be used for advanced analyses of multigirder bridges. The calibration procedure is demonstrated using actual truck data collected at a representative set of weigh-in-motion (WIM) stations in New York State. Extreme value theory was used to project traffic-load effects to different service periods. The results are presented as live-load models developed for a 5-year typical rating interval and for a 75-year design life. The outcome of the calibration indicates that maximum traffic-load effects can be calculated using finite-element models with the help of a single truck for short to medium one-lane multigirder bridges and two side-by-side truck configurations for multilane bridges. The proposed analysis trucks have axle configurations of the standard AASHTO 3-S2 and Type 3 legal rating trucks with appropriate factors to amplify their nominal weights. The amplification factors reflected the presence of overweight trucks in the traffic stream and the probability of multiple presence. The proposed live-load models are readily implementable for deterministic refined analyses of highway bridges and for evaluating the reliability of bridges at ultimate limit states considering the system’s behavior.

Many bridge management systems use Markov models to predict the future deterioration of structural elements. This information is subsequently used in the determination of optimal intervention strategies and intervention programs. The input for these Markov models often consists of the condition states of the elements and how they have changed over time. This input is used to estimate the probabilities of transition of an object from each possible condition state to each other possible condition state in one time period. A complication in using Markov models is that there are situations in which there is an inadequate amount of data to estimate the transition probabilities using traditional methods (e.g., due to the lack of recording past information so that it can be easily retrieved, or because it has been collected in an inconsistent or biased manner). In this paper, a methodology to estimate the transition probabilities is presented that uses proportional data obtained by mechanistic-empirical models of the deterioration process. A restricted least-squares optimization model is used to estimate the transition probabilities. The methodology is demonstrated by using it to estimate the transition probabilities for a reinforced concrete (RC) bridge element exposed to chloride-induced corrosion. The proportional data are generated by modeling the corrosion process using mechanistic-empirical models and Monte Carlo simulations.

This paper introduces a novel low-damage bridge column design for accelerated bridge construction (ABC) in seismic areas. The proposed design integrates (1) polyurethane (PU) damage-resistant segments at the column ends to accommodate large rotations without damage, (2) external replaceable energy-dissipating (ED) links to provide supplemental hysteretic damping and flexural stiffness and strength, and (3) internal unbonded posttensioning to provide self-centering. Polyurethanes are polymeric materials that exhibit large deformability, low stiffness, and large strength, in addition to rate-dependent elastic and inelastic mechanical properties. As a result, PUs can accommodate large deformations with negligible damage. The ED links are external buckling-restrained yielding steel elements, which offer additional stiffness/strength and hysteretic energy dissipation to control seismic-displacement demands. Following strong earthquakes, residual deformations are small and can be fully eliminated upon replacement of the (external) ED links, which are the only elements to experience major damage. Because all ED links are external, replacement can be rapidly performed without operation disruptions. The mechanical properties of a selected PU were first investigated through uniaxial compression tests for various strain rates. The proposed column design was then investigated for various PU-segment geometries and various ED-link properties through three-dimensional finite-element analysis of a bridge column subjected to monotonic and cyclic pushover loading at various loading rates and amplitudes. The proposed column design was found to provide major self-centering and energy-dissipation capabilities with negligible damage. The response was found to be dependent on the geometric properties of the PU segments. Residual deformations significantly decreased with the loading rate. However, the peak column strength only slightly increased with the loading rate.

Structural health monitoring (SHM) has become a very important research area for evaluating the performances of bridges. An important issue with continuous SHM and damage detection of bridges is the effects of temperature variations on the measurement data, which can produce bigger effects in the response than the damage itself. In this study, a sensor-clustering-based time-series analysis method integrated with artificial neural networks (ANNs) was employed for damage detection under temperature variations. The damage features obtained solely using the time-series-based damage-detection algorithm are very effective for damage assessment; however, they yield false positives and negatives when temperature variations are present. Therefore, ANNs were used to compensate the temperature effects on the damage features obtained from time-series analysis. This methodology is applied to a footbridge finite-element model in which 2,000 simulations with temperature effects and damage cases were conducted. Results reveal that the proposed method can successfully determine the existence, location, and relative severity of damage using output-only vibration and temperature data even when temperature variations are present.

Tens of thousands of aging, bridge-class, RC box culverts are in service in the United States. Within the context of establishing load rating for in-service RC box culverts, this paper introduces, calibrates, and applies a system-level pavement-stiffness model to a production-simplified, soil–structure interaction model used for calculating load demands. The proposed pavement-stiffness model uses system-level pavement data to account for the additional stiffness provided by the pavement structure to attenuate live load. The full cover-soil depth is modeled using linear-elastic finite elements per the production-simplified soil–structure interaction model, and the additional stiffness provided by the pavement structure is modeled using beam elements across the top row of finite-element nodes. Equivalent beam-modulus values for the system-level pavement-stiffness model were calibrated against results from a research-intensive, full-pavement model for various pavement types. A parametric study using the proposed model showed that the inclusion of pavement stiffness could increase the load ratings for both asphalt pavements with an intermediate thickness and concrete pavements, for both direct-traffic and low-fill RC box culverts. The effects of the system-level pavement-stiffness model on predicted live-load moment response were further evaluated using measured live-load moments from field live-load tests on in-service culverts. From these comparisons, the system-level pavement-stiffness model showed improved accuracy and precision of the live-load demand prediction. Finally, load-rating analyses performed for an illustrative sample of 24 in-service Texas RC box culverts under various pavement types showed improved rating factors from the system-level pavement-stiffness model compared to the production-oriented soil–structure interaction model without pavement stiffness and the AASHTO-recommended structural-frame model. The inclusion of the pavement stiffness when modeling in-plane live-load attenuation improves the RC box culvert load-rating results and can be implemented for systemwide infrastructure management.

The design and construction of spread slab beam bridges is becoming commonplace in Texas. Although this relatively new class of bridge is somewhat similar to spread box beam bridges, it is unclear whether the existing live load distribution factor (LLDF) equations for the latter system are applicable for the former. Therefore, this paper presents the evaluation and derivation of flexural and shear LLDFs for the new spread slab beam bridge class. Thirty-one variations of these models were used to investigate an array of possible bridge geometries, and shear and moment LLDFs were derived for the design of spread slab beam bridges. Twenty-eight additional geometries were explored to derive correction factors for skew angle, overhang, and vehicle position. Existing AASHTO spread box beam bridge LLDFs range from being unconservative to very conservative when applied to spread slab beam bridges. Therefore, new LLDF expressions are developed to provide an appropriate estimate of load sharing for spread slab beam design in terms of moment and shear.

Two kinds of relations between flutter derivatives and aerodynamic admittance functions (AAFs), which have been used in bridge aerodynamics, are discussed in this study by means of theoretical analysis and experiments. The first kind, called substitutive Kϋssner function method in this study, assumes equivalence between the Wagner function and the Kϋssner function. In doing so, the AAFs can be calculated based on flutter derivatives. The other one involves a concept of equivalent Theodorsen function, and the relation is built up by utilizing the classic relation between the Sears function and the Theodorsen function. Both methods are reasoned to be logically problematic in this study. Furthermore, these relations were examined with wind tunnel experiments. Flutter derivatives and AAFs of a flat plate and a rectangular cylinder with an aspect ratio of 4 were tested. The measured AAFs were compared with those calculated from flutter derivatives. The results show that, as frequency increases, the gap between the measured AAFs and those by the substitutive Kϋssner function method increases drastically. In comparison, the AAFs based on equivalent Theodorsen functions are closer to measured results in the low-frequency range; however, as frequency increases, they deviate from the measured AAFs in the form of violent oscillation, streamlined and bluff sections alike. It is shown that this kind of fluctuation originates from the illogicality inherent in the method.

Fires from vehicular accidents involving heavy-goods vehicles (HGVs) pose a significant threat to steel plate girder highway bridges. The complete immersion of plate girders in flames resulting in excessive girder element temperature is hypothesized to be a gauge of the fire performance of highway bridges. This research investigated the effect of girder geometry on the flame dynamics and fire performance of typical steel girder–concrete deck highway bridges. As part of the study, the thermo-structural response of a standard single-lane steel girder–concrete deck composite assembly made of three plate girders and a single tub girder exposed to a HGV fire was evaluated. It was predicted that the single-lane highway bridge made with plate girders would fail with exposure to a HGV fire, whereas the bridge with a tub girder was predicted to maintain structural integrity for the total fire duration. The tub girder design was determined to provide superior resistance to collapse compared with multiple-plate girders because of its lower temperature rise and higher moment resistance. The study also investigated the effect of inclusion of a flame shield between the plate girders and multiple tub girders on the fire performance of highway bridges.

The strut-and-tie model (STM) has been adopted as a preferred methodology for the design of disturbed regions; however, an aspect that has not yet been sufficiently cleared up is the service behavior of structural concrete designed at the ultimate limit state. To address this issue, this paper is devoted to developing an advanced elastic-to-plastic strut-and-tie model (EPSTM) to capture the full elastic and inelastic response of the anchorage zones. The principle of stationary complementary energy is introduced into the STM to generate the adaptive EPSTM at each load step automatically. The proposed EPSTM provides a consistent analysis of the behavior of anchorage zones, including the average strain of struts and ties, load-deformation response, and the maximum crack width, throughout the loading process, and it has been verified to be sufficiently accurate when compared with testing results.

Current sliding-bearing designs do not make full use of the stiffness and potential ability of sliding piers in the aseismic design of continuous bridges. Aiming at the problem that the demand on the only fixed-pier force and beam-end longitudinal displacement is too large under longitudinal direction earthquakes, an aseismic design idea of a continuous bridge is proposed based on coloading of all piers by installing locking balls between the sliding piers and the continuous girder. This device can also handle displacement caused by rise and drop in temperature. When a strong earthquake occurs, the locking ball is activated, and the locking connections between the girder and the sliding piers were built to let the sliding piers carry the longitudinal seismic load of the superstructure in conjunction with the fixed pier. A vibration-table experiment on a three-span continuous bridge with a scale of 1:25 was conducted, and results were compared with finite-element model (FEM) simulations. The aseismic effect and the mechanism of the locking ball on the continuous bridge were analyzed. The results showed that the sliding piers can bear the longitudinal seismic load of the upper structure in conjunction with the fixed pier under strong earthquake conditions and can improve the overall aseismic performance of the continuous bridge significantly. Meanwhile, the seismic demands on the sliding piers increased. The number of spans and the length of the continuous girder had an influence on the locking-ball aseismic effect. However, the variation of temperature had little influence on the aseismic effect of the locking ball.

This study presents a new nominal flexural resistance of composite I-girder sections using high-performance steel, HSB600, in the positive bending region. Unlike conventional steels, HSB600 undergoes strain hardening immediately after yielding. To compare the flexural behavior of composite girder sections using HSB600 with that of conventional composite steel girder sections, a moment-curvature analysis was performed. To take into account the effects of strain hardening on the flexural resistance, the strain-hardening plastic moment was introduced as a substitute for the full plastic moment. An extensive parametric study using the strain compatibility method was conducted for a wide range of composite girder sections, and the relationship between the ratio of the strain-hardening plastic moment to the full plastic moment and the ductility ratio was determined. On the basis of the results of the parametric study, a factor that accounts for the strain-hardening effects is suggested as a function of the ductility ratio. A new nominal flexural resistance for the composite HSB600 girder sections is then proposed, defined as the product of the nominal flexural resistance in the AASHTO LRFD Bridge Design Specifications and the strain-hardening factor.

Today, railroads carry 40% of the United States’ freight tonnage, and the demand for this service is expected to double in 20 years. The railroad infrastructure contains more than 100,000 bridges spanning over 225,000 km of tracks. Half of those bridges are over 100 years old. Accordingly, safe and efficient railroad operations depend on the continuous maintenance of this aging bridge network. Recent research has demonstrated that bridge displacements can be utilized as an indication of structural integrity in the prioritization of maintenance, repair, and replacement (MRR) operations. However, existing response-measurement methods either require expensive technological instrumentation or are based on complex structural modeling assumptions. Furthermore, many of them do not accommodate real-time monitoring. This paper proposes a new methodology fusing multimetric measurement data obtained from reference-free sensors, such as accelerometers and tiltmeters, in real time to provide accurate transverse displacement measurements inexpensively. Twenty-four percent of railroad bridges in the United States are timber. Therefore, to study the performance of the proposed method, a realistic train-crossing event was simulated by using a numerical model of a timber pile bent. Timber piles were simplified as free-standing cantilever beams accounting for the soil–structure interaction based on literature and industry input. The model was excited dynamically with real train input loads collected at the site. The analysis reproduced nonsymmetric bridge responses, including pseudostatic displacements observed in the field, which conventional accelerometers cannot measure. The pseudostatic displacements from tiltmeter data were extracted using simple Euler-Bernoulli beam equations that can be estimated for any railroad timber pile bent, requiring only the length of the pile above ground as the input. These pseudostatic responses were combined with dynamic displacements derived from accelerometer data, allowing the estimation of the transverse displacement in the field without the need of a finite-element model. Researchers compared measured responses to displacements estimated by the proposed data-fusion method. The results indicate that transverse bridge displacements can be determined by combining pseudostatic and dynamic responses in real time more precisely compared to previous methods. Consequently, more effective MRR prioritization can be undertaken with accurate response measurement.

Suspenders are crucial load-bearing members of suspension bridges, and they are prone to fatigue damage under repetitive vehicle and wind loads. Field observation shows that short suspenders at the midspan or the ends of bridges may be more vulnerable. This study investigated the influence of using rigid central clamps on the fatigue performance of short suspenders, and two finite-element models of a long-span suspension bridge, with and without central clamps, were developed for comparison. Results show that central clamps can significantly mitigate the bending stress of short suspenders by reducing the relative motion between cables and the girder. Although wind-induced stresses of suspenders are smaller in amplitude than those induced by the vehicle load, the wind loads also contribute significantly to fatigue damage of suspenders because of the large number of stress cycles. Based on a vehicle-load model and the wind spectrum developed from field-monitored data, a fatigue life evaluation procedure was developed, and the fatigue lives of suspenders of the bridges with and without central clamps were calculated, respectively. Results suggest that when there are no central clamps, suspenders may have fatigue lives shorter than the design value.

In past decades, significant progress has been made in prediction of the behavior of posttensioned anchorage zones. An aspect that has not been sufficiently cleared up yet, however, is the service behavior of posttensioned anchorage zones designed at the ultimate limit state, especially with regard to crack formation. To address this problem, a numerical method based on the cohesive crack model is proposed to investigate crack propagation in posttensioned anchorage zones and predict structural behavior in the service state. These numerical analyses of the tested anchorage zone specimens show that the proposed procedure can describe crack-propagation behavior accurately, including first cracking load, crack length, crack width, crack trace, and ultimate load. To control crack width in the service state, parameter analysis, based on the proposed method, is performed. The results show that for concentric anchorage zones, proper bar diameters and bar spacing can lead to significant decreases in crack width, whereas the stirrup contributes little to cracking control.

The functionality of the U.S. transportation infrastructure system is dependent upon the health of an aging network of over 600,000 bridges, and agencies responsible for maintaining these bridges rely on the process of load rating to assess the adequacy of individual structures. This paper presents a new approach for safety screening and load-capacity evaluation of large bridge populations that seeks to uncover heretofore unseen patterns within the National Bridge Inventory database and establish relationships between select bridge attributes and their load-capacity status. Decision-tree and random-forest classification models were trained on the national concrete slab bridge data set of over 40,000 structures. The resulting models were validated on an independent data set and then compared with a number of existing judgment-based schemes found in an extensive survey of the current state of practice in the United States. The proposed approach offers a method that provides guidance for improved allocation of resources by informing maintenance decisions through rapid identification of candidate bridges that require further scrutiny for either possible load restriction or restriction removal.

Coupled fatigue and corrosion is more detrimental for RC bridge deck slabs than either fatigue or corrosion separately. The main objectives of this study are to obtain a greater understanding of the deterioration mechanisms and failure modes of RC bridge deck slabs subjected to coupled fatigue and corrosion. Analysis of the joint interaction between chloride-induced steel corrosion and fatigue cracking of concrete is presented. Moreover, the effects of fatigue cracking on the chloride diffusion process and the influences of internal forces redistribution caused steel corrosion on the reinforcement-fatigue stress range were studied. On the basis of the coupled fatigue-corrosion damage mechanism, two fracture-failure modes of concrete bridge decks were proposed and the corresponding limit state functions were deduced. Finally, the performance assessment of an illustrative example shows that the coupled fatigue-corrosion effects obviously reduced the fatigue life of RC bridge deck slabs. It was concluded that the effects of coupled fatigue and corrosion should not be neglected in the fatigue safety design of RC bridge decks.

Prefabricated reinforced concrete column connections employing grouted sleeve (GS) splices enable rapid construction, are familiar to contractors, and their detailing resembles cast-in-place (CIP) construction. Previous studies showed disrupted plastic hinge formation in the stiff sleeve region. The proposed design method shifts the plastic hinge location above the sleeve region, which effectively increases the plastic rotation capacity and ductility. Plastic hinge shifting was realized by using transition splicing and high-strength steel reinforcement in the connecting element (footing). The proposed method was investigated experimentally using two 0.42-scale column tests under slow cyclic loading and a series of uniaxial tensile tests. Results indicate that good ductility can be achieved compared with conventional CIP construction and previously tested GS connections details. Experimental and analytical moment-curvature results were used to support discussion of design considerations and of an approximate method for calculating the displacement ductility of precast columns with GS connections and shifted plastic hinging.

Fabric-reinforced cementitious matrix (FRCM) is a relatively new material system developed for the repair, retrofit, and rehabilitation of reinforced concrete (RC) and masonry structures. Structures such as bridges experience high traffic volumes and varying vehicle axle weights causing repeated cyclic loading throughout the lifetime of the structure. Cyclic loading may cause progressive damage to the structure, a phenomenon known as fatigue. Due to the novelty of FRCM technology, there is a lack of research regarding the long-term performance of FRCM systems for RC strengthening. This study investigated experimentally the parameters that most influence the flexural fatigue performance of polyparaphenylene benzobisoxazole (PBO) FRCM-strengthened RC beams. Specimens are subjected to both static and cyclic (fatigue) loading. For members subjected to cyclic loading, the following parameters were investigated and discussed: amount of supplemental reinforcement, ultimate strength, applied stress range, fatigue life, failure modes, and residual strength. Results were used to develop a stress ratio versus the number of cycles (S-N) curve with the objective of defining the endurance limit of the FRCM strengthened RC beams.

This study aims at developing appropriate multilevel performance classification of tall RC bridge piers for seismic design. A new performance classification toward postearthquake rehabilitation requirements is presented. It considers damage states of the local environmental conditions and accessibility of the potentially damaged part. To reduce postearthquake rehabilitation requirements, higher performance levels allowing only minor and moderate damages are advised for tall bridge piers. Two RC columns with high aspect ratios were designed, fabricated, and tested under static cyclic loading, focusing primarily on minor and moderate damage states such as residual concrete cracking and onset of visible concrete crushing. The experimental results show that the zero-tip-displacement crack width measured after the column returned to zero tip displacement significantly underestimated residual-cracking damage, while the zero-lateral-force crack width can be taken as an approximate estimation for the residual cracking on the safe side. An improved model is proposed to evaluate the cracking behavior beyond steel yielding. In this model, the expected residual-crack width is expressed as a function of the maximum crack width. The results obtained using the model show good agreement with the experimental results. For the onset of concrete crushing, 24 cantilever test columns in total were analyzed, with aspect ratios equal to or greater than 3.0 and axial-load ratios ranging from 0.05 to 0.25. The results indicate that a higher aspect ratio and lower axial-load ratio lead to a higher drift ratio corresponding to the onset of visible concrete crushing.

The perfobond rib (PBL) shear connector group composed of multiple layers of PBL shear connectors has been proven to be one of the most effective load-transferring components and is widely used in cable-stayed bridges. In this study, an analytical method was developed to analyze the internal force transfer of a PBL shear connector group, based on the nonlinear equivalent stiffness of key components, which include the shear connectors, perforated steel plate, and concrete base. Explicit analytical expressions of the internal force distribution among different layers of shear connectors were derived and validated against experimental results. Uneven force distributions resulting from the different equivalent stiffnesses of different layers of shear connectors were demonstrated. Key factors influencing the load distribution include the stiffness of the perforated steel plate, concrete base, and shear connectors. The unevenness of the load distribution was found to gradually decrease with the development of plastic deformation of the shear connectors. The proposed method offers an efficient and practical approach to investigating the mechanical behavior of a PBL shear connector group and quantifying its property of uneven internal force distribution.

This study presents a methodology for estimating stay cable tensions of cable-stayed bridges using genetic algorithm (GA) and particle swarm optimization (PSO). At first, a comprehensive cable model was used to represent the dynamic behavior of the cables. Second, an error function corresponding to the difference between the experimentally measured natural frequencies of the cable and the analytical natural frequencies (obtained using the preferred cable model) was introduced. GA and PSO were then used for minimizing the error function to estimate the cable tension. Because of the stochastic nature of evolutionary algorithms (EAs), results of the minimization problem were reported statistically over multiple runs. Following the proposed methodology, bending stiffness of the cable, sag extensibility, and the effect of the cable crossties (that are used to suppress the wind- and rain-induced vibration of cables) were considered. The accuracy of the proposed method was evaluated using simulation results of a tensioned cable and experimental results of a cable-stayed bridge.

Surface roughness, ice accretion, and atmospheric turbulence are important issues because they can considerably alter the aerodynamic characteristics of bridge cables. The present study describes wind-tunnel experiments on vortex-induced vibrations of rough bridge cables characterized with various surface roughness and performed at various levels of atmospheric turbulence. Three different cable models were used: a smooth cylinder to represent dry cables, a helical strand cable, and a cable with modeled ice accretion. The studied parameters include the critical velocity and amplitude of vortex-induced vibration and parameter sensitivity to changes in flow turbulence and cable surface roughness. The results obtained indicate that cable roughness and turbulence of the flow have significant influences on the dynamic response of bridge cables. The experimental results indicate that the vortex-induced vibration was largest for the ice-accreted bridge cable.

In this article, a field test of a large-span soil–steel bridge is described. The case study involved a corrugated steel plate that was stiffened by concrete rings. The rings were applied to make it possible to use only one layer of steel plate while covering a span as long as 20 m. The test involved deflection and strain measurements of the steel plate under increasing layers of soil. The test results show that both maximum deflection and the maximum bending moment occurred at the crown when the soil reached the crown level. Conversely, the maximum axial force occurred at the bottom of the arch when the soil reached its maximum level above the arch. The test results were compared to the well-known design methods of soil steel bridges. According to the results, the design methods are conservative in predicting bending moments, but they are more realistic in predicting axial forces.

Overweight vehicles may cause permanent damage to bridge superstructures and thus require a permit to operate and route planning based on bridge capacity. This study explores the possible damage of such overweight vehicles to concrete bridge decks. Concrete cylinders in this study were subjected to compressive stresses, equivalent to 40 to 80 percent of the measured strength of concrete, followed by 300 freeze–thaw cycles to simulate field conditions. The effects of combined loading and the freeze–thaw cycles were evaluated using rapid chloride ion penetration tests of samples sliced from the cylinders. The test results indicated that the chloride ingress in deck concrete can be affected by heavy trucks.