Journal of Bridge Engineering

This study presents a novel approach to simulating the fatigue stress spectra of short- to medium-span bridges under stochastic and dynamic traffic loads. The stochastic traffic load is simulated based on the weigh-in-motion (WIM) measurements of a heavy-duty highway bridge in China, and the dynamic effects are modeled using a vehicle-bridge coupled vibration system. An interpolation RSM is used to approximate the effective stress ranges of a bridge with respect to road roughness conditions, gross vehicle weights, vehicle configurations, and driving speeds. The RSM provides a platform for an efficient spectrum simulation of bridges under stochastic and dynamic traffic loads. A case study of a simply supported T-girder bridge demonstrates the effectiveness and efficiency of the proposed approach. The proposed computational framework provides an effective approach for simulating the fatigue stress spectra for short- to medium-span bridges with WIM data. However, the efficiency of the approach depends on the number of intervals of driving speed and gross vehicle weight in the interpolation RSM. Additionally, overloading control has a considerable influence on the probability density of the high-amplitude stresses in the fatigue stress spectrum. Even a relatively high overloading limit value will considerably increase the fatigue reliability of a bridge. In addition, the numerical results provide a theoretical basis for bridge deck retrofitting and truck overloading control measures.

The cross-section warping effect and warping-induced long-term prestress loss due to creep are investigated in this paper. Both phenomena were analyzed deterministically and stochastically. The random character of concrete creep and environmental factors have substantial effects on the statistical scatter of the total prestress loss. To obtain the real development of concrete long-term performance, sophisticated models for concrete creep and shrinkage prediction were used. The Monte Carlo–Latin hypercube sampling method was applied to capture the statistical variability of boundary and environmental conditions. It is shown that the severity of cross-section warping can be important, particularly in the case of short spans and unevenly distributed and isolated tendons in a cross section. The three-dimensional effects and the statistical variability of creep are considered to enable reliable design of box girder bridges.

A new ultraseismic waveform tomography technique for a bounded medium is presented for evaluation of concrete bridge abutments, or wall piers, and the supporting soil and rock underneath them. Ultraseismic wave fields are measured on top of abutments and inverted by a full waveform inversion (FWI) technique. The technique includes forward modeling to simulate wave propagation for estimated waveform data and a cross-adjoint inversion to match estimated to measured data for the extraction of material properties (S- and P-wave velocities, or V_S and V_P) of the tested medium. For the forward modeling, because wavelengths of the intended ultraseismic waves (200–1,200 Hz) in concrete are several times that of the thickness of a bridge abutment, the abutment is considered a thin plate. A finite-difference solution of two-dimensional (2D) elastic wave equations in a thin plate was used for the forward simulation. The presented FWI technique was applied to two synthetic data sets generated from realistic bridge abutments supported directly by soil-and-rock or pile foundations. The results revealed that the waveform analysis was able to characterize accurately both the V_S and V_P profiles of abutments and the supporting soil-and-rock or piles underneath them. Abutment depths, embedded low-velocity anomalies, and individual pile tops were clearly identified.

Based on the theory of beams on elastic foundation (TBEF), the potential correlation between corrosion-induced configuration alteration and seismic behavior of long-span cable-stayed bridges with a floating system is investigated qualitatively. Some factors associated with initial configuration of those bridges, i.e., the influence length of bending moment, critical buckling load, and buckling mode, are determined first by the energy method. The correlation of the factors with cable corrosion is then identified by using the TBEF. Through an example bridge excited by earthquakes, development of plasticity hinges and yielded cables, load-carrying capacity, and buckling resistance is studied to reveal their potential relationship with corrosion. The study indicates that corrosion in cables can alter the positions in which the first plasticity hinge and the first yielded cable occur. The development of subsequent plasticity hinges and yielded cables also has exhibited a strong relationship with cable corrosion. Corroded cables tend to cause a decrease in earthquake resistance of those bridges. Severe corrosion can possibly switch intentionally from design failure mode to undesirable bucking failure.

The objective of this project is to investigate the causes of premature deterioration of a number of existing finger-plate and flat-plate expansion devices under high traffic volumes and to suggest new designs and retrofits for improved performance. The main contributions to the failure of the finger-plate expansion devices were found to be fatigue failure of the weld between the finger plate and the support beam as well as vertical misalignment due to poor construction. The dynamic impact of truck traffic was also found to be a contributing factor. The failures of flat-plate expansion devices were generally initiated by misalignment of the sliding plate and support angle due to rotation in the bridge span or poor alignment during construction. Experimental testing showed that the dynamic impact in the finger-plate device is generally between 40 and 70% and could be as much as 160%, and the effect of misalignment of the fingers can result in an increase in stress of up to 30%. The experimental results were used to validate finite-element models (FEMs), which also show high stresses in the weld between the finger plate and support beam concentrated over the stiffener location. New and retrofit designs of the finger-plate connection device concentrated on the use of bolted connections to reduce stress concentrations, to improve support structure, and to increase adjustability for alignment.

Scour of bridge piers has been demonstrated to be one of the most common causes of bridge instability and destruction. This article presents a long-term approach to scour depth determination for a cable-stayed bridge based on time-varying modal parameters generated from a structural health monitoring system. The finite-element model, updated according to dynamic testing before opening the bridge to traffic, was employed to identify the sensitive modes for scour depth variation and establish the numerical relationship between scour depth and the modal parameters. Afterward, the time-varying modal parameters were determined using monitored acceleration data sets. Numerical investigation has indicated that these modal parameters are also significantly impacted by environmental conditions, which will cause confusion when determining scour depth. Nonlinear principal component analysis (NLPCA) was chosen to separate the environmental influence from the scour depth influence on modal parameters. Finally, comparison of the scour depth determined based on modal parameters with the results of visual inspection by divers exhibits the effectiveness of the proposed approach. Moreover, this study could provide guidelines for future decision making regarding the early warning and maintenance of bridge piers.

Automated techniques for analyzing the dynamic behavior of full-scale civil structures are becoming increasingly important for continuous structural health-monitoring applications. This paper describes an experimental study aimed at the identification of modal parameters of a full-scale cable-stayed bridge from the collected output-only vibration data without the need for any user interactions. The work focuses on the development of an automated and robust operational modal analysis (OMA) algorithm, using a multistage clustering approach. The main contribution of the work is to discuss a comprehensive case study to demonstrate the reliability of a novel criterion aimed at defining the hierarchical clustering threshold to enable the accurate identification of a complete set of modal parameters. The proposed algorithm is demonstrated to work with any parametric system identification algorithm that uses the system order n as the sole parameter. In particular, the results from the covariance-driven stochastic subspace identification (SSI-Cov) methods are presented.

A rapid evaluation methodology for steel girder bridges was researched and executed for this study. The goal was to conduct a field evaluation and load rating within a single day. To achieve this goal, three initial tasks were performed: laboratory testing to determine rapid sensor attachment, the establishment of field instrumentation guidelines, and code development to automate the data processing of crawl-speed load-test field measurements. The instrumentation guidelines and data-processing code allow for the identification of several parameters that are critical to properly representing the functional behavior of the structure. These critical parameters include composite behavior, live-load distribution factors, and presence of span continuity. With these parameters and readily available user input values, AASHTO HL-93 live-load ratings can be determined. The overall methodology was validated through a case study of a load-restricted three-span steel girder bridge. The structure was field evaluated over 1 day to produce load ratings on site. The controlling load rating of the structure prior to testing was 0.45 (operating level), which was increased to 1.56 as a result of a reduction in live-load distribution factors and the presence of composite behavior. The findings of the research illustrate the feasibility and value for rapid assessment of bridges that can potentially be incorporated into regular bridge inspection schedules.

For existing bridges, proof-load testing can be a suitable assessment method. This paper addresses the evaluation of a posted reinforced concrete slab bridge over a highway through proof-load testing, detailing the preparation, execution, and analysis of the test. As the target proof-load and the required measurements for proof-load testing currently are not well-defined in the existing codes, this pilot case was used to develop and evaluate proposed recommendations for proof-load testing for a future guideline on proof-load testing for the Netherlands. Moreover, the pilot proof-load test is used to study the feasibility of proof-load testing for both shear and flexure.

Bridge widening is commonly required in congested bridges. During construction, one or two lanes on the old bridge remain open; the vehicle traffic generates vibrations affecting the early age concrete of the closure pour, which may induce a negative effect on the durability of the bridge, i.e., initial crack in the closure pour. To quantitatively evaluate the mechanical performance of closure pours under vibration load, this paper examined three construction schemes for closure pours in bridge-widening projects. An equivalent full-scale segment model was designed to test the three schemes, including vibration tests and static tests. In the vibration tests, the setting time, the development of deflection, strain, and cracking of the closure pour during the construction period were obtained. Adding I-shaped steel beams to restrain the movement of the old and new bridges significantly improved the performance of the closure slab. In the static test, the final load-carrying capacity, damage, and failure modes were investigated. The slabs poured with the restraining steel beams showed superior crack resistance performance. The peak load-carrying capacity of the closure pour was about 50 times the maximum expected load, demonstrating the satisfactory load-carrying capacity of the closure pour.