Journal of Bridge Engineering

Large structures such as tall buildings, towers, and bridges transfer their loads to competent soil layers through pile skin friction and/or end bearing. When a pile is installed in a compressible soil layer, it may experience additional skin frictional force called drag force due to excessive soil settlement relative to the pile. This paper reports the results of a comprehensive long-term monitoring program of instrumented bridge piles and adjacent soil to evaluate the development of drag forces along the shafts of three piles. The data collected from the monitoring program are presented and discussed in terms of measured responses with time and load distribution along the pile shafts. The data were used to compute and locate the extent of the drag force for each of the three piles and to determine the end of the consolidation process. In addition, the results were used to examine the unified design method and assess the design codes with respect to drag force.

To more accurately describe the mechanical behavior of prestressed steel strands with symmetrical wires breaking in unbonded post-tensioned concrete beam, this paper establishes the equilibrium equation after the bending deformation of the broken wire, taking into consideration bending deformation of the broken wires and the friction between wires and duct. The results derived from this equation fit well with the experimental data. The increase of friction between the center and outer wire and the friction between the broken wire and duct can reduce the recovery length and the strain ratio of the unbroken wire within the recovery length. The increase of axial force before wires breaking will increase the recovery length and the strain ratio of the unbroken wire within the recovery length. The rise in the number of broken wires can reduce the strain the broken wire fully recovers to and recovery length and increase the strain ratio of unbroken wires within the recovery length. In addition, we find that the stress of the unbroken wires near the breaking end becomes greater after symmetrical wires breaking, which is harmful to the structural safety. If there is corrosion in the unbroken wires near the breaking ends, these wires are likely to break immediately following the symmetrically broken wires.

The hysteretic behavior of bolt connections in a timber–concrete composite (TCC) bridge was investigated. Six identical TCC specimens were designed with bolted connections and subjected to reversed cyclic loading tests. The failure modes, energy dissipation capacity, stiffness degradation, strength degradation, and hysteretic responses of the specimens were evaluated. The experimental results indicate that the predominant failure mode was a dual-hinge mechanism in the bolts of the TCC specimens. The TCC specimens exhibited satisfactory energy dissipation and achieved a mean ductility factor of 6.76. A finite-element model was developed to simulate the cyclic response of the tested TCC specimens. The simulated data are in good agreement with the experimental data. The experimental and numerical results reported are useful for the development of design guidelines for TCC bridges with bolted connections.

Numerous bridges in the mountainous areas of southwest China are constructed with tall reinforced-concrete (RC) piers. This paper presents the influence of higher-mode effects of pier columns on seismic performance in a quantitative manner for, to our knowledge, the first time, while the impact of excitation intensity and the frequency content of input motion, which do not appear to be considered in any previous study, are incorporated as well. Numerical models are developed for three bridges with different pier heights, considering higher-mode effects by comparing the seismic responses computed from multi-degree-of-freedom and single-degree-of-freedom systems. An incremental dynamic analysis method is used to investigate the influence of input intensity, and motions matching different target spectra are employed, showing the effects of frequency components. The analytical results show that when the tall piers remain elastic or experience substantial nonlinearity approaching the ultimate state, the higher-order modes contribute more significantly to the seismic responses, while input excitations with more low-frequency components could generally suppress the effects of higher-order modes. Based on the analysis, seismic design strategies for tall piers are discussed and a novel design scheme using preset plastic region length is proposed, which is demonstrated to be able to limit the range of damage with a negligible increase in maximum curvature demand.

Abstract

Current practice only considers the net (average) thrust for in-service engineering assessment of buried corrugated steel culverts (CSCs). In this study, numerical simulations have demonstrated, for shallow cover depth conditions (H/D < 2), the importance of local peak thrust and combined load effects (i.e., thrust and moment), which occur between the CSC shoulder and crown locations. These observations are supported by independent, third-party, full-scale, physical modeling studies. A global sensitivity analysis was conducted to identify the influential variables, assess the significance of any interaction, and estimate the influence on the predicted response. Based on this analysis, a limit state function for combined load effects and modification factor to account for the local peak thrust force was developed. The reliability index for the proposed coefficients was also established.

Practical Applications

For culverts buried at depths greater than twice the culvert diameter, current engineering practice can be used, with confidence, to estimate the average (net) circumferential force (thrust) developed in the culvert wall. As the culvert burial depth is reduced, there is less confidence in predictable outcomes with shallower cover depth where the top of the culvert (crown) is located closer to the ground surface. In this study, numerical simulation tools have shown that current practice underestimates the magnitude (value) of the circumferential forces developed in comparison with numerical modeling predictions. The numerical models demonstrate that the response of shallow buried culverts is influenced by both circumferential forces and bending forces where the peak local force is greater than the net thrust. A mathematical equation is developed that accounts for the changes in the culvert circumferential force and bending force with burial depth that can be used to guide engineering design.

Structural deterioration is induced by multiple mechanisms due to progressive degradation, such as aging, corrosion, and fatigue, and sudden events, such as earthquakes, tsunamis, and hurricanes. These mechanisms may significantly affect the performance indicators of structural components and systems during their life cycles. Many studies on the effects of structural deterioration on structural performance indicators have been reported in the literature. However, most of them study the effect of a single deterioration mechanism on structural performance indicators in a deterministic context. Therefore, further research is needed to capture the joint effects of multiple deterioration mechanisms on structural performance indicators in a probabilistic context. Moreover, in order to achieve the main goal of infrastructure management by maximizing the life-cycle performance at a minimum cost, an optimal risk-based life-cycle strategy has to be provided. This paper presents a life-cycle risk-based optimal management strategy for bridge networks subjected to corrosion and seismic hazards. The proposed strategy is illustrated with an existing bridge network. Girder replacement is considered for the bridge superstructure, which is prone to corrosion hazard, while seismic retrofit measures are considered for the bridge bearings and substructures to improve their seismic performance. A709-50CR steel girders are used to replace the corroded steel girders herein (A709-50CR is a novel corrosion-resistant steel with a chromium content similar to that of martensitic stainless steel). Parametric analysis is conducted to investigate the effects of both target service life and correlation of the safety margins among the superstructures of the bridge network on the Pareto fronts associated with life-cycle risk-based optimal maintenance solutions. Comparison is also made between Pareto fronts associated with both hazards and those associated with corrosion hazard only.

The base metal at a stop-hole edge will be in out-of-plane torsion under bending loads to resist bolt tightening and weaken the reinforcement effect. By carrying out numerical simulation and fatigue tests, the effect of bolt reinforcement for stop-holes under out-of-plane bending loads was analyzed and the influence degree of reinforcement form, pretightening force, and eccentric loading on the maintenance effect were clarified. By carrying out real bridge application and dynamic stress monitoring, the effect of bolting for cracks subjected to out-of-plane deformation was explored. The results demonstrate that bolt reinforcement can significantly restrain the in-plane tension and out-of-plane shear deformation and alleviate fatigue damage accumulation at the crack tip to arrest continuous growth. The reinforcement effect of double bolts is remarkable and will not cause excessive local stiffness to induce new fatigue cracking. An excessive increase in the pretightening force cannot effectively improve the reinforcement effect and even aggravates the risk of cracking at the bolt edge, while a reasonable ratio of loading amplitude to pretightening force is approximately 3:1. The fatigue life of components is negatively linearly related to the nominal stress at the bolt, according to which the fatigue life can be quantitatively evaluated.

Steel plate girders are considered a viable solution for the construction of medium- to long-span bridges. Despite their many advantages, various concerns have been raised regarding their maintenance due to the potential of fatigue crack initiation at welded details, accelerated corrosion in thin webs, and trapped debris around stiffeners. The use of rolled beams, on the other hand, can be very beneficial because they require much less maintenance. However, they are limited in size, which imposes constraints on their use to relatively short-span bridges due to deflection requirements. In this study, the behavior of the double composite superstructure system was investigated. The system comprises rolled beams in combination with a reinforced concrete slab, resting on the bottom flanges of the beams, to allow for longer spans to be built using rolled beams. To assess the full potential of double composite bridge systems, an analytical formulation, validated through numerical finite-element analysis, was developed to capture the full nonlinear behavior of the bridges. The effect of some parameters relevant to the performance, such as the use of prestressing tendons and ultrahigh-performance concrete, was investigated. The analysis results showed a substantial reduction in deflection for the double composite bridges over their single composite counterparts. Similarly, a significant increase in the moment capacity was also shown when the double composite sections were used. The finite-element modeling approach was used to reflect on the localized response of a selected bridge. The analysis procedure outlined in this study could be applied for the design and assessment of double composite bridges and could be used to determine the viability of using such a system for the construction and rehabilitation of new and existing bridges.

The traditional objective function (TOF) of bridge model updating is usually defined on the basis of the structural response residuals between numerically calculated and experimentally measured values. However, this model finds it difficult to determine the weighting factors, and the updated model lacks accuracy. To offset these disadvantages, this study proposes a novel objective function (NOF) for finite-element model updating of a long-span cable-stayed bridge using in situ static and dynamic measurements. The proposed NOF comprises the residual functions of the displacement assurance criterion, the position of the neutral axis, and the natural frequency. The global sensitivity analysis–based model updating uses the Kriging model as the surrogate model to save computational costs. The nondominated sorting genetic algorithm II is employed to find the Pareto solutions. The updating results with the TOF defined directly using displacement, stress, and frequency are listed for the purposes of comparison. The results show that the NOF avoids determining the weighting factors and provides more accurate results than the TOF. The updated displacement curves, the position of the neutral axis, and the frequencies obtained from the NOF are all closer to the experimentally measured ones than those obtained from the TOF. After model updating, the displacement’s relative errors are around 5% without considering the displacement values under 10 mm. The relative errors of the first four frequencies are all less than 10%. The updated model can serve as the baseline finite-element model of the bridge.

Vortex-induced vibrations (VIVs) remain a key issue for slotted box girders. To clarify the influence of additional structural elements on the aerodynamic characteristics of a double-slotted box girder for highway and railway hybrid bridges, wind tunnel tests involving the pressure distribution, VIV responses, and wake measurements were performed. The wind pressures and vortex-shedding frequency characteristics of a bridge were compared under different additional structural element combinations of balustrades, wind barriers on highways and railway deck surfaces, maintenance rails, and so on. The results indicated that the maintenance rails had a limited influence on VIV characteristics and distributed pressures of the double-slotted box girder. However, owing to the stronger disturbance of the wind barriers and balustrades on the highway deck surface, unsteady shear flow separating from the wind barrier top acts on the middle and leeward girders, resulting in large-amplitude torsional VIVs to generate considerable excitation forces. Moreover, because wind flow across the slotted parts interacted with the girder and additional structural elements, stronger torque forces were generated. Consequently, correlation and contribution were enlarged, which corresponded to large-amplitude torsional VIVs. This provides a reasonable explanation for the considerable influence of wind barriers on highway decks on torsional VIVs. Moreover, with regard to the double-slotted box girder [especially the upper surface of the windward girder, upper and lower surfaces of the leeward girder, and windward gap of the three girders (Regions II to IV, VI, and X to XI, respectively)], the distributed wind pressures acting on the characteristic parts of bridge decks further contributed to the generation of torsional VIVs.

The further development and improvement of prediction models for crowd-induced vibrations of footbridges requires detailed information on representative operational loading data. In this paper, an inverse method is used to estimate the parameters that govern human–structure interaction from the resulting structural response. The parameters of interest concern the dynamic characteristics of a mass-spring-damper (MSD) system, applied to describe the mechanical interaction between the pedestrian and the structure. The dynamic characteristics of the MSD interaction model are estimated by minimizing the discrepancy between the observed and the simulated power spectral density of the structural response. The parameter estimation procedure assumes that the dynamic behavior of the empty structure, the average weight, and the distribution of step frequencies in the crowd are known. The proposed approach is verified using numerical simulations and the influence of modeling errors is investigated. The results show that as footbridges and the human body are by nature lightly ($\lesssim$2%) and strongly (≈30%) damped, respectively, the structural response is most sensitive to small variations in the natural frequency of the MSD interaction model. The results, furthermore, show that the parameter estimation problem is mostly sensitive to errors related to the mean value of the distribution of step frequencies and the structural modes’ natural frequency and modal mass. The impact of the structural modeling errors is found to decrease as the impact of human–structure interaction increases. Next, the approach is applied to two real footbridges where the walking behavior and the structural response induced by high pedestrian densities are observed. The results show that an estimate of the natural frequency (≈3.0 Hz) and damping ratio ($\approx 34\text{\%}$) of the MSD interaction model is obtained that is in accordance with recent findings in the literature. These estimates are, however, for the first time ever, it is believed, based on full-scale observations involving high pedestrian densities.

Classifiers based on machine learning algorithms trained through hybrid strategies have been proposed for structural health monitoring (SHM) of bridges. Hybrid strategies use numerical and monitoring data together to improve the learning process of the algorithms. The numerical models, such as finite-element (FE) models, are used for data augmentation based on the assumption of the existence of limited experimental data sets. However, a numerical model might fail in providing reliable data, as its parameters might not share the same underlying operating conditions observed in real situations. Meanwhile, the concept of transfer learning has evolved in SHM, in particular through domain adaptation techniques. The ability to adapt a classifier built on a well-known labeled data set to a new scenario with an unlabeled data set is an opportunity to transit bridge SHM from research to practice. Therefore, this paper proposes an unsupervised transfer learning approach for bridges with a domain adaptation technique, where classifiers are trained only with labeled data generated from FE models (source domain). Then, unlabeled monitoring data (target domain) are used to test the classification performance. As numerical and monitoring data are related to the same bridge, both domains are assumed to have similar statistical distributions, with slight differences caused by the uncertainties inherent to the FE models. The domain adaptation is performed using a transfer knowledge method called transfer component analysis, which transforms damage-sensitive features from the original space to a new one, called latent space, where the differences between feature distributions are reduced. This approach may increase the use of numerical modeling for long-term monitoring, as it overcomes some of the limitations imposed by the calibration process of FE models. The efficiency of this unsupervised approach is illustrated through the classification performance of classifiers built on source data with and without domain adaptation, and using the benchmark data sets from the Z-24 Bridge as the target data.

Abstract

Previous research conducted multiple levels of laboratory tests and analytical studies and designed an innovative joint to resist joint cracking on the longitudinal joint between box girders. The joint design was165 mm (6.5 in.) wide and filled with shrinkage-compensating concrete and reinforced with transverse steel bars. Although the previous laboratory test and analytical simulation results indicated that the joint showed superior performance when resisting the joint early-age cracking and maintained the integrity of the bridge superstructure, its performance on a real onsite bridge was not evaluated. This paper documented the field evaluation of this new design on a single span box beam bridge. A bridge in Washington County, Iowa was selected to deploy the joint. To evaluate the performance of this first implementation, a 7-day field monitoring campaign was conducted during the early-age of the joint material. In addition, a live load field test and two bridge inspections at 6-month intervals were performed. During the field tests and monitoring work, temperature, strain, and displacement data were collected at critical locations and analyzed to evaluate the joint functionality on cracking resistance and load distribution. The visual inspections were conducted and focused on the condition and performance of the joint with a specific interest in the development of any cracking. The results indicated that this new joint was well suited to resist early-age joint longitudinal cracking, which is common in other joint designs. The joint was efficient in load distribution and the bridge superstructure behaved as an integral structure when the live load was placed. In addition, with an integral abutment, the construction of the abutment affected the strain distribution in the joint near the joint ends. This effect tended to provide compression in the transverse direction and reduced the potential of joint cracking.

Practical Applications

This paper documents the field evaluation of the new design of a longitudinal joint between concrete box beams on a bridge in Washington County, Iowa. The joint was 165 mm (6.5 in.) wide and filled with shrinkage-compensating concrete and reinforced by transverse steel bars. The results indicated that this new joint was well suited to resist early-age joint longitudinal cracking, which is common in other joint designs. The joint was efficient for load distribution. The bridge superstructure behaved as an integral structure when the live load was placed. In addition, with an integral abutment, the construction of the abutment affected the strain distribution in the joint near the joint ends. This effect tended to provide compression in the transverse direction and reduced the potential of joint cracking. This design is recommended to be used in concrete box beam bridges to prevent longitudinal joint cracking and reduce the potential of bridge superstructure deterioration, especially in rural regions. Further research is recommended to deploy the design on a bridge with a higher traffic volume to investigate the performance of the joint under larger traffic loads.

The geometry and structural behavior of steel box girders with large cantilevers utilized in cable-stayed bridges are intricate. Due to the large cantilever, the transverse stress in the steel box girder cannot be ignored. To investigate the transverse stress distribution law of the steel box girder, a test was conducted on a 1:4.5 scale segment of a cantilever steel box girder in a cable-stayed bridge model. The distribution patterns of the transverse stress in the top and bottom plates of the steel box girder under six distinct load cases were analyzed. It was discovered that positive and negative transverse stresses appeared simultaneously in the top plate when solely subjected to the train load, whereas this phenomenon did not occur in the bottom plate. Furthermore, an improved simplified analytical model was proposed for predicting the transverse stress of the steel box girder. In comparison with the results of the test model, the rationality of the simplified analytical model was substantiated. Moreover, on the basis of the simplified analytical model, the phenomenon of concurrently occurring positive and negative transverse stresses was explained, and the maximum transverse stress distribution in the top and bottom plates under the action of a unit moving load was obtained. The location of the maximum transverse stress in the top and bottom plates was also discussed. The outcome of this paper could serve as a reference in the design of steel box girders with large cantilevers in cable-stayed bridges.

Many factors are considered when inspecting and evaluating the overall condition of a bridge. Of particular consideration here is load testing of bridges to evaluate the existing load-carrying capacity. Sensor systems are often mounted directly to girders for this assessment; however, installing sensors and data acquisition systems can be an expensive and time-consuming process, particularly given that load testing does not warrant long-term monitoring. As an alternative, noncontact remote sensing techniques have been developed for measuring structural deformations, and have the potential to be used for static load test applications. These approaches do not require sophisticated instrumentation installations, and can provide a denser array of measurements, compared with conventional sensors. A particular focus has been on techniques that use video recordings, tracking the motion between subsequent video frames via computer vision methods. There are now commercial offerings for such measurement systems, as well as an array of techniques that can be used for custom applications. While such methods have seen significant testing under laboratory conditions, there are only a limited number of studies that provide comparative methodological analyses under full-scale field conditions. This paper presents a case study on the use of vision-based methods for bridge load testing, and provides a comparison of a digital image correlation (DIC) approach with a phase-based optical flow method. Two sets of field experiments were performed on bridges in the state of Delaware. The results show that vision-based methods can provide comparable results to conventional sensor installations, given sufficient consideration of the unique technical demands of these methods, as well as operational logistics. In most cases, the DIC and phase-based methods provided comparable results, though the DIC system yielded generally better accuracy, owing to a combination of algorithmic differences and additional signal postprocessing.

The steel–concrete hybrid girder bridge structure is a combination of steel and concrete members in the direction of the bridge length. In long-span segmental concrete box girder bridges, the utilization of lightweight steel girders in the middle portion of the main span would greatly reduce the bridge self-weight while decreasing concrete creep and shrinkage effects. A critical parameter in the design of hybrid girder bridges is the rational length of the steel portion as a part of the main span (in other words, the rational location of the steel–concrete connection). Based on the concept of system equivalence, the steel–concrete hybrid system is equivalent to a full-concrete system with a reasonable span arrangement. The governing condition of the equivalence is that both systems have the same magnitude of self-weight hogging bending moments over the piers. Applying the system equivalence method, the rational length ratio of the steel portion to the main span (ξ) is explicitly solved, and its relationship with the length ratio of side span to main span (λ) is established. Finally, the proposed analytical approach is validated by five case studies, indicating that it is an effective and efficient method for the preliminary design of hybrid girder bridges.

In this paper, the fatigue performance of six steel–concrete composite beam specimens was tested following subjection to chloride-induced corrosion and cyclic freeze–thaw conditions. The specimens included cast-in-place concrete slab composite beams with uniformly distributed studs and precast concrete slab composite beams with a cluster distribution of studs. According to the climatic characteristics of large temperature differences between day and night in alpine and high-altitude areas of Qinghai Province of China, together with the working conditions of bridges under deicing salt after snow, corrosion tests and freeze–thaw tests of composite beam specimens were performed prior to fatigue testing. The test results show that the freeze–thaw cycle causes obvious frost heave damage to the concrete, which affects its strength and stiffness. When the composite beam specimens were subjected to fatigue loads, tearing failure of the steel plates at the welds and interface failure at the studs were observed. Furthermore, with the influence of stress amplitude, fatigue life was found to be related to the initial crack defect within the specimen itself. Reduction in the initial stiffness of composite beams was found to be affected by the freeze–thaw cycle, stud arrangement type (uniformly distributed or cluster distributed), and steel type (ordinary steel or weathering steel). However, the stiffness degradation rate of all specimens against loading times was essentially identical before fatigue failure.