Journal of Bridge Engineering

Hydraulic factors have become the principal causes of bridge failures since the 1990s. They account for around 50% of bridge failures in the database constructed by the present authors. Hydraulic failures generally occur without early warning, with significantly destructive results. These kinds of failures are expected to continue in the future due to the increasing climate change all over the world. This paper is intended to have a comprehensive review of up-to-date work on hydraulic bridge failures due to three factors: scour, flood, and floe ices. First, we conduct a historical statistic analysis for bridge failures, especially focusing on the causes and features, based on around 1,700 cases collected over the past 200 years. Then, we review the failure modes and prediction methods for the hydraulic bridge failures due to scour, flood, and floe ices, respectively, and discuss some relevant examples and applications adopted in the current practices. The aim of this paper is to provide a concise but comprehensive summary of information needed by researchers and engineers to understand the mechanisms of the hydraulic failures of bridges and how current practices deal with these issues. Much work has been dedicated to determining what future research is required to furtherly understand the subject and find improved solutions to these existing problems. We hope that this review will provide a concise but comprehensive summary of information needed by researchers and engineers to understand the mechanisms of hydraulic failures of bridges and how the current practices deal with these issues.

The conventional precast segmental concrete column may suffer severe damage in concrete segments and yield significant residual deformation when subjected to a strong earthquake. To achieve the goal of low-damage seismic design for accelerated bridge construction in high seismicity areas, a precast column using concrete-filled double-skin steel tube (CFDST) segments is a promising candidate. In this study, an innovative posttensioned precast segmental CFDST (PTPS-CFDST) column is proposed, and four PTPS-CFDST column specimens considering the effects of external energy dissipation (ED) devices and initial prestressing forces were tested under lateral cyclic loading to explore their seismic performance. The mechanical features of the testing PTPS-CFDST columns including damage pattern, hysteretic characteristics, ED capacity, prestressing force variation, residual displacements, joint opening, curvature distribution, and concentrated rotations were compared and discussed. Testing results revealed that the PTPS-CFDST column has good seismic performance, good self-centering capacity, and minor seismic damage; the column deforms with multiple joint rotations; the reasonably arranged ED devices can effectively improve the ED performance; and a relatively high prestressing force enhances the strength and stiffness of the column. This study achieves a deeper understanding of the seismic performance of the innovative PTPS-CFDST column, which may provide references for the seismic design of this new type of bridge piers.

Monitoring the magnitude of stay-cable forces over time can play a key role in assessing the integrity and safety of a cable-stayed bridge. A variety of methodologies have been proposed to estimate stay-cable forces, with vibration-based methodologies being most widely applied in real-world applications due to their simplicity, speed, and economy. In most cases, periodically performed pluck tests are used to excite a cable, and accelerometers mounted on the cable are used to record its vibrational characteristics. Taut string theory (TST) is then applied to compute the cable forces. Because a pluck test is required to excite the cable, cable force measurements conducted in this manner are only done periodically. In this paper, we are interested in accurately computing stay-cable tensile forces on a more continuous basis using wind-induced cable vibration data collected by permanently installed structural health monitoring (SHM) systems. The specific objectives of this study are to (1) compute bridge stay-cable tensile forces over time using SHM data and use the results to establish confidence intervals (CIs) that can be applied to future cable force computations to detect “abnormal” values that might signal changes in bridge condition, and (2) define the wind characteristics (speed, gust, and direction) that lead to “acceptable” vibration records from which accurate cable forces can be computed. By fully understanding the wind load effects on cable vibrations, bridge owners will better know under what wind conditions to collect cable accelerations data. By knowing which data is useful, the amount of data collected and analyzed can be minimized, and the accuracy of the force calculations can be increased. The impact of wind load characteristics on the accuracy of cable force calculations is a key component of this work. To validate the proposed methodologies, data collected by an SHM system on the Indian River Inlet Bridge, a cable-stayed bridge in southern Delaware, was used. More specifically, the accelerations of eight cables recorded during five “storms” and one “regular” two-week ambient event (all occurring from 2014 and 2021), were evaluated. During the events, ambient weather conditions (i.e., mean wind speed, wind gust, wind direction, temperature, and perception) were collected in 5-min intervals. Cable accelerations were processed using power spectrum density to identify natural frequencies of the cables. TST was then applied to compute cable tensile forces. By doing this over an extended time window, 99% CIs for expected values of stay-cable forces were computed. These CIs can be used to monitor computed stay-cable forces over time as a means for assessing cable and overall bridge condition. While computing cable forces, it was found that some acceleration records did not yield accurate natural frequencies. Decision tree (DT) models were built to identify the wind load characteristics that correspond to cable vibrations that do yield accurate frequencies. The DT methodology was applied to establish a common set of wind load conditions for all cables for accurate frequency and cable force calculations. By establishing a set of wind load conditions for a specific bridge, those monitoring the bridge can minimize the amount of data collected, while improving the accuracy of the stay-cable force calculations.

Abstract

To promote accelerated bridge construction (ABC), precast bridge columns are now being more widely used in engineering applications. Researchers have often studied the seismic performance of precast bridge columns, but the study of shear performance is quite limited. The main purpose of this study is to investigate shear behavior of low-aspect-ratio precast columns with grouted sleeve connections considering the effect of axial load ratios. Cyclic quasistatic tests of four 1/4-scaled reinforced concrete precast column specimens were conducted to investigate their seismic performance. The experimental results showed that large axial load reduced ductility factor of columns, but increased lateral force capacity. A predicting method for lateral force capacity of precast bridge columns based on a strut-and-tie model in the sleeve region was developed. The method can realistically predict the lateral force capacity and take into the influence of axial load on lateral force capacity of precast columns with grouted sleeve connection.

Practical Applications

Grouted sleeve connections have been one of the most effective connections for precast columns in prefabricated bridge construction. For urban expressway bridge engineering, there are many columns with low aspect ratio. Lack of corresponding performance evaluation methods of the short columns with grouted sleeve connection restricts its application in medium- and high-intensity earthquake zones. This study revealed damage mechanisms of precast column under cyclic load, such as shear crack, shear slip of joint, and failure modes of joint connection. In addition, a strut-and-tie model was proposed to accurately predict lateral bearing force for precast columns with grouted sleeves under various axial load ratios. The achievement of this study can provide theoretical support for seismic design of short columns (aspect ratio less than 2.5), and the related research results have been applied to the engineering construction of urban bridges in medium- to high-intensity areas such as Jingxiong Expressway, Zunqin Expressway, and Shanghai S26 Expressway.

The shear behavior of prestressed concrete (PC) beams is a complex problem because there are many influential parameters involved. Currently, the code-based shear strength of PC beams is primarily based on empirical equations, which tend to be overconservative and are unable to generalize to different cases (e.g., beams with or without stirrups). This paper presents a framework to develop an explainable, data-driven model for the shear design of PC beams over a wide range of parameters. To this end, a comprehensive data set was assembled, consisting of 670 experiments of PC beams with and without stirrups. Different machine-learning (ML) techniques, including Random Forest, AdaBoost, and XGBoost, were evaluated to define a predictive model for the data set. Then, the most accurate model (based on XGBoost) was optimized to achieve high accuracy (with a coefficient of determination of 0.98 for the testing set). Moreover, the Shapley Additive exPlanations technique was used to explain and evaluate the importance of different parameters on the output of the predictive model. The predictive model was shown to be largely more accurate and more generalizable than current design equations and advanced finite-element analysis. In addition, reliability-based shear strength reduction factors were derived for the proposed ML model. These reduction factors allowed the application of the proposed ML model in the code-compliant shear design of PC beams.

Recently, due to low cost and convenience, the concept of estimating the bridge’s first natural frequency through indirect measurements of a passing vehicle has gained increasing attention—known as drive-by bridge structural health monitoring. As the vehicle acts as a moving mass added to the bridge, this system is nonstationary with time-varying characteristics. Most related studies assume constant bridge and vehicle frequencies of vehicle–bridge interaction (VBI), which is only appropriate when the VBI effect is negligible. When the vehicle mass is significant compared with the bridge mass, often a feature of railway bridges, the interaction effect cannot be ignored. Therefore, this paper presents a nonlinear time–frequency analysis approach to examine the time-varying nature of frequencies in the VBI system using the second-order synchrosqueezing transform. In comparison to the classical linear approaches, such as wavelet transform and short-time Fourier transform, the proposed method can significantly improve the energy concentration of the time–frequency representations, resulting in a clear pattern to show how the frequencies change. In addition, an indicator is proposed to automatically select the parameters with the proposed approach to obtain suitable results. Both numerical simulation and laboratory experiments are carried out to investigate the feasibility of the proposed approach. It is found that due to the time-varying nature of VBI, the frequencies of both vehicles and bridges are time-varying. Therefore, the extracted drive-by bridge frequency should be distinguished from that found using direct (on-bridge free vibration) measurements.

The neglect of the cyclic creep of concrete induced by vehicles may overestimate the deflection reliability of long-span prestressed concrete (PSC) box-girder bridges and increase structural safety risks. In this paper, a novel method considering the combined effects of the shrinkage, static creep, and cyclic creep of concrete and the stress relaxation of prestressed tendons is proposed to assess the time-dependent deflection reliability of PSC box-girder bridges. By employing the Kelvin chain model, the conventional integral-type method for calculating the static creep of concrete is converted to rate-type creep analysis, which has a higher computational efficiency and can consider various nonlinear effects. The cyclic creep of concrete is estimated by the fatigue mechanics-based model and integrated into the quasi-elastic incremental constitutive model. The proposed constitutive model is implemented in a general finite-element program DIANA, in which the mechanical behavior of the thin-walled box girder is described by the composite degenerated shell elements. An importance sampling method is applied when estimating the deflection reliability to balance the computational accuracy and efficiency. The proposed method is applied to a long-span PSC box-girder bridge with a main span of 150 m. The results indicate that the cyclic creep of concrete may accelerate the reduction of the deflection reliability indexes, which may fall below the target level before the expected service life of the bridge. In addition, heavy trucks passing in pairs have a significant impact on the deflection reliability. The research findings can be used for the reliable design and optimal maintenance of long-span PSC box-girder bridges.

In the last few decades, structural health monitoring (SHM) has proven a helpful tool to support the maintenance and management of civil infrastructure. However, typical measurement networks are expensive and require considerable initial efforts. The user-friendliness and interpretability of the outcome of SHM systems are crucial factors in motivating infrastructure owners and decision-makers to sustain their costs. For this reason, simple algorithms that provide structural parameters with direct physical interpretability for professionals familiar with the typical quantities involved in structural engineering are still the most used in field applications. This paper proposes an original method to identify curvature influence lines of bridges and viaducts only using the structural acceleration response induced by vehicular loads. Acceleration time histories collected at sparse locations through standard accelerometers are employed. In contrast to SHM approaches based on modal parameters, the proposed method does not need strict synchronization, thus being suitable for wireless and low-cost monitoring solutions. Identified influence lines are used to define a spatially dense damage indicator for accurate localization of structural anomalies with a clear physical meaning. Experimental results obtained for a steel truss bridge analyzed in different damage conditions prove the efficacy of the proposed method for situations where modal-based approaches may fail.

The wind field characteristics of a bridge site are the key issues for driving the safety assessment condition of mountain canyon terrain. Field measurements on a bridge deck were conducted to investigate the microclimate wind environment at the vehicle level. The measurement points were arranged in the midspan and bridge tower regions along the bridge at vehicle height above the bridge deck. The height-dependent characteristics of the microclimate wind environment at the midspan and bridge tower regions were extensively analyzed. The results show that the mean wind profiles at midspan approximately confirm the power exponential distribution. However, the mean wind profiles show non-power-exponential distribution at the tower regions. The vertical mean wind speed profiles at the midspan and bridge tower regions were then statistically fitted and suggested. The wind speed distribution at the bridge tower regions showed obvious shielding or acceleration effects. Therefore, a typical wind envelope curve across the tower region was proposed along the driving direction. For the turbulence characteristics, turbulence intensities at the tower regions are larger than those at the midspan, and integral scales at the tower regions are smaller than those at the midspan. In this study, a double logarithm third polynomial was recommended to depict the energy distribution of the turbulence microclimate wind in the frequency domain instead of the commonly used empirical spectrum functions. Gust wind speeds were also discussed, and showed that gust wind speeds are more reasonable for evaluating vehicle driving safety and comfort in long-span bridges, especially at the tower regions.