Journal of Bridge Engineering

Results are reported from tests of three precast, prestressed concrete girders under fatigue-type cyclic and monotonic loading conducted after deck removal and replacement. Although deck demolition altered the top surface of the girders, the girder–deck interfaces exhibited shear strengths greater than their nominal strength (based on the 2012 AASHTO LRFD Specification) after 2 × 10⁶ cycles of loading to 45 and 30% of their nominal strength for troweled and roughened interfaces, respectively. A partially debonded detail was used for two of the girders to protect the girder top flange, which was wide and thin, during deck demolition. The roofing felt used to debond the girder–deck interface over the flanges reduced the effort required for deck removal by 65%, compared with the typical detail, eliminated chipping hammer–induced damage to the girder flanges, and still resulted in sustained composite action under 2 × 10⁶ cycles of loading. The width of the bonded interface had little effect on girder stiffness and no observed effect on the width of deck effective in bending.

Precast segmental bridges made of ultrahigh-performance concrete (UHPC) have gained wide research attention and application. The shear transfer of dry joints between UHPC segments is one of the major concerns due to the discontinuity and interruption of the reinforced bars. In this study, direct shear tests of UHPC joints were conducted. Parameters included confining stress, concrete type, joint type, joint shape and number of keys, and arrangement of steel reinforcement. Crack-formation sequences, cracking patterns, ultimate shear load, and vertical slippage were obtained, and typical normalized shear stress–relative displacement curves were calculated. The results show that a higher shear strength of UHPC joints can be achieved with higher confining stress, higher matrix tensile strength, and the addition of steel fibers. Concrete joints with fibers exhibited a limited area of concrete crushing compared with joints without fibers. Large-keyed joints showed a minor increase in shear capacity (9.7%) compared with three-keyed joints. A calculation method for the shear strength of concrete dry joints based on Mohr’s circle was established, and a simplified formula for calculating the shear strength of UHPC dry joints with different compressive strengths was developed. The results of the proposed calculation method were found to agree well with the experimental values. The average ratio of the calculated results to the experimental results was found to be 1.01, with a standard deviation of 0.14. The simplified formula for UHPC joints was also found to have better agreement with the shear test results, with an average ratio of 0.96 and a standard deviation of 0.24, compared with 1.41 and 0.38, respectively, in the AASHTO provisions.

A new concept for a deployable autonomous control system (DACS) was recently developed by the authors to achieve short-term vibration mitigation in lightweight structures. With the details of the deployability and autonomy aspects having already described, this article focuses on experimentally evaluating the performance of the DACS in suppressing the lateral vibrations of pedestrian bridges. A real-time hybrid simulation (RTHS) methodology was employed as the experimental tool to achieve this goal. In the RTHS procedure employed in this study, the pedestrian bridge was modeled numerically, and the DACS was tested physically on a hydraulic shake table that reproduced the bridge displacements. The RTHS methodology is a well-established experimental technique for lumped-parameter building structures, but it involves implementation challenges when applied to pedestrian bridges where the location of the load is spatially varying. Using modal decomposition principles, a discrete state-space formulation is presented that can be used for the RTHS of bridges. This method allows moving loads and DACS mobility to be considered during RTHS. Following the experimental modeling of the DACS prototype, the reliability of the characterized DACS model was validated through a series of single-degree-of-freedom hybrid simulations. The RTHS of a pedestrian bridge equipped with the DACS was carried out to experimentally evaluate the effectiveness of the DACS. A linear-quadratic Gaussian-based controller capable of compensating for the interaction effects between the structural response and DACS is presented.

Measuring static or dynamic displacement is often an integral component of evaluating bridge conditions. This article introduces a wireless, low-cost, and high-accuracy smart radar sensor network to measure bridge displacement. This sensor technology consists of two major systems, a continuous-wave radar sensor and a wireless smart sensor network platform. The continuous-wave radar sensor, paired with an active transponder, has demonstrated submillimeter accuracy for structural displacement measurements. The hardware and software designs of the sensor network are presented in this article. The WiSeMote wireless sensor platform is adopted to establish a sensor network synchronized to the microsecond level. Critical performance metrics of the sensor network are quantified, including power consumption and wireless transmission range. The sensor network’s static and dynamic measurement accuracy have also been verified in a series of pedestrian bridge experiments. In addition, the ability of the sensor network to detect the vehicle speed is validated.

In this paper, a new damage index is proposed for RC bridge piers using the concept of earthquake input energy distribution in a structural system. The damage index was defined as the ratio of the hysteretic energy to the earthquake input energy to take into account the cumulative effects of stiffness degradation, inelastic deformation, and material nonlinearities throughout the loading history. A damage-assessment method was also developed in accordance with material strain. For this purpose, a set of circular RC bridge piers tested under cyclic/seismic loadings was simulated to calibrate the reliability of the proposed damage index and strain-based damage limit states. The results confirmed the ability of the damage index to predict the damage levels of piers under cyclic and seismic loading. The damage index was also compared to some existing damage indices. The comparison showed that the proposed damage index is a relatively simple and practical approach that can provide a reasonably gradual progression of damage throughout the loading history more convincingly than other damage models.

For bridges under seismic excitations, current design practices recommend to comply with the capacity protection principle for pile foundations. However, in cases, such as elevated (or scoured) RC pile-cap foundation typologies that are partially embedded, the piles may suffer large deflections under lateral loads, which make it difficult for them to remain in the elastic state. In this regard, the present study makes an in-depth analysis on the ductile behavior of elevated RC pile-cap foundations to explore potentials for seismic ductile design. A beam-on-nonlinear-Winkler-foundation model with or without the consideration of bond-slip effect at pile head/cap connections is built in accordance with quasi-static testing of a 2 × 3 elevated RC pile-cap foundation, and validated in various aspects, including the global force-displacement relationship, the failure mechanism, and the location of plastic hinges. The validation results indicate that the bond-slip effect is generally unremarkable and can be neglected for the modeling of studied elevated pile-cap foundations (EPFs). Two limit states and the corresponding ductility factors, named easy-to-repair and ultimate displacement ductility factors, are proposed for EPFs. Parametric pushover analyses are then performed to investigate the impact of structural and geotechnical parameters on the ductile behavior of real-scale 2 × 3 elevated RC pile-cap foundations embedded in homogeneous and multilayered cohesionless soils. The numerical results show considerable ductile capacities (with an average quantified as 2.77 and 4.05 for the easy-to-repair and ultimate displacement ductility factors, respectively) for elevated RC pile-cap foundations. Additionally, a mathematical relationship between displacement and curvature ductility factors is established for future ductility-based design practices.

Thin-walled steel tubular columns with circular cross sections are widely used as cantilever piers in bridges due to their excellent structural and constructional advantages. However, local buckling, global buckling, or the interaction between both is usually the main reason for the significant strength reductions in these columns, which eventually leads to their collapse. This article investigates the behavior of thin-walled steel tubular columns with conventional uniform circular sections (Cs) and newly proposed graded-thickness circular sections (GCs) under combined constant axial and cyclic lateral loading. The analysis is carried out using a finite-element model (FEM) that takes into account both material and geometric nonlinearities. First, the accuracy of the employed FEM is substantiated using the experimental data available in the literature. Then, the GC column with a size and volume of material equivalent to the C column is introduced. The proposed GC column is proved to have significant improvements in strength, ductility, and postbuckling behavior compared with its counterpart C column. As part of the investigation, an extensive parametric study is carried out to investigate the effects of various important parameters, such as radius-to-thickness ratio parameter (R_t), column slenderness ratio parameter (λ), magnitude of axial load (P/P_y), and number of loading cycles (N), on the strength and ductility of the columns. Finally, design formulas for strength and ductility evaluation of C and GC columns are proposed.

Mechanical fasteners are used in composite structures to physically connect steel and concrete components. Composite action is developed primarily by transferring horizontal shear forces through dowel-type connections. Welded headed studs are a conventional dowel-type product for cast-in-place construction. For this reason, the shear response of these types of fasteners has been extensively studied. In some cases, the tensile strength of a stud connection needs careful consideration, such as when evaluating the ultimate capacity of a composite bridge suffering girder damage. Observations from a detailed testing program demonstrated the importance of accurately characterizing the tensile response of a stud connection in determining when the onset of collapse will occur. In this paper, the response of a stud connection within a haunch configuration is characterized under tensile loads to provide essential data for determining the ultimate capacity of a composite bridge having steel girders and a reinforced concrete deck. Empirically derived equations to estimate the tensile strength of a stud connection and its corresponding displacement are proposed based on a data regression analysis. In addition, a method to account for strength reduction due to combined shear and tension forces is introduced using an interaction equation.

Half-through steel plate girder bridges are widely used across the United Kingdom’s railway network. However, few studies have investigated their real in-service behavior. Concurrently, the use of advanced sensor systems, such as those utilizing fiber-optic sensors, have begun to find widespread use in structural health monitoring due to their high accuracy and long-term stability and durability. In this paper, the real performance of a newly constructed skewed half-through plate girder railway bridge was assessed using an integrated fiber optic monitoring system installed during the bridge’s construction. Monitoring data recorded during the passage of 12 separate trains consisted of strains measured along the length of the main steel plate girders and crossbeams. Based on available design and construction information, a three-dimensional finite-element model capable of simulating the railway bridge’s response was constructed and used to investigate and provide comparisons with monitoring results of the performance of such bridges under passing trains. The influence of track cant on load distribution between the two main girders was discussed, and the live load utilization percentage of the main girders was estimated to be approximately 37% of its design capacity. In addition, the effect of different transverse crossbeam end-connection details (pinned or moment connected) and the influence of axle load distribution through track ballast on the overall response of the bridge structure were evaluated. The results obtained in this study have not only led to the establishment of a comprehensive performance baseline for the newly constructed bridge for long-term condition monitoring but may also be used for improving the design and in-service structural evaluation of such bridges.

Serviceability requirements are crucial in the design of fiber-reinforced-polymer (FRP) RC bridge members. Permissible crack width under service loads is one of the requirements that can control design. Crack-control models have been included in the Canadian and American design codes based on experimental work on FRP-RC members with rectangular cross sections. In this study, the applicability of these models to RC bridge members with a circular cross section was assessed experimentally. A total of nine full-scale, circular RC specimens measuring 0.5 m in diameter and 6 m in length were constructed and tested up to failure under a four-point bending load. The test parameters included the longitudinal-reinforcement ratio and the longitudinal-reinforcement type, including glass FRP, carbon FRP, basalt FRP, and steel bars. The experimental results were reported in terms of crack patterns, crack spacing, and crack width versus flexural tension-bar strain and the applied moment. Crack-control models in the current FRP codes and design guidelines were re-examined, extended, and applied to circular FRP-RC members. Design equations for estimating the service stress in the FRP reinforcement and the cracked moment of inertia were theoretically derived and presented for the circular FRP-RC members. Crack-width predictions were compared with the experimental results. The comparison indicated that the crack-control formulae developed for rectangular FRP-RC members can be used for the cracking control of circular FRP-RC members by using the redefined parameters developed and proposed in this study to take into account the geometry, bar spacing and distribution, and effective tension stiffening area.

Past reconnaissance studies revealed that bridges close to active faults are more susceptible to damage, and more than 60% of the bridges in California are skewed. To assess the combined effect of near-fault (NF) ground motions and skewness, this paper evaluates the seismic vulnerability of skewed concrete box-girder bridges in California subjected to NF and far-field (FF) ground motions. The relative risk of skewness and fault-location on the bridges is evaluated by developing fragility curves of bridge components and system accounting for the material, geometric, and structural uncertainties. The skewness and a bridge site close to active faults make bridges more vulnerable, and the existing modification factor in Hazus cannot capture the variation in the median value of the fragilities appropriately. A new set of fragility adjustment factors for skewness coupled with the effect of fault location is suggested in this paper.

Long-span cable-stayed bridges usually adopt a semifloating system scheme to reduce the internal force of seismic response. However, the seismic measures based on conventional fluid viscous dampers (FVDs) cannot prevent excessive displacements in the beam-ends as well as adverse stress in the members under both dynamic and static cases, especially when the damping is comparatively lower or the beam-ends accumulate displacements due to the configuration of the dampers. To address this issue within reasonable cost, a new type of elasticity-damping composite device was developed for the Zhuankou Yangtze River Highway Bridge in Wuhan, China. This paper presents the merits of the device by introducing its constitution, installation, and working mechanism, as well as mechanical studies in the design process. The device, combining a damping system and a disk spring system, was designed to have restorable elasticity in a specific mechanism. The mechanical model of the device was conceived by estimation of a reasonable connection between the pylon and the deck. Then, the parameters of the model are determined mainly by comparison and parametric studies for a rational combination of strength, stiffness, and damping of the structure. Static finite-element (FE) and nonlinear time history (NTH) analyses are performed in the studies to satisfy the static and seismic demands, respectively. The procedure reveals a comprehensive advantage of the device in framework, damping effects, and static behaviors, followed by the validation analysis in more general cases.

Complicated temperature fields and crossing high-speed trains offer new challenges for monitoring girder deflections in operating railway bridges. Behavior analyses and early warning of girder deflections are necessary for the diurnal operation of bridge structures. Regarding the Nanjing Dashengguan Yangtze River Bridge, the present paper identifies the temperature-induced/train-induced deflections of the bridge girder from deflection data obtained from the wavelet transform. The principal components of the bridge temperature field are obtained to verify the temperature sensitivity of the girder deflection. The effect of the temperature-induced girder deformation on train-induced girder deflections is analyzed using the train-bridge dynamic model. The statistical laws of the downward and upward of train-induced girder deflections are described using the t location-scale distribution. Based on the mutual updating of monitoring data and numerical model, the behaviors of the temperature-induced/train-induced deflections of the bridge girder can be captured accurately, and the warning threshold of girder deflections under the coupling effects of temperature and trains is determined rapidly. The results demonstrated that the influence of the temperature-induced girder deformation on the train-induced girder deflection is relatively small when compared with the train-induced girder deflection itself, with the increasing amplitude being no more than 3%. A real-time early warning of girder deflections for the long-span railway bridge can be conducted to indicate the abnormal changes in girder deflection less than 10 s, which is likely due to the deterioration of track irregularity on the bridge or damaged bridge components.

Information on deformation is critical for bridge condition evaluation, but accurate characterization, usually via discrete displacement measurements, remains a challenging task. Vision-based systems are promising tools, possessing advantages of easy installation, low cost, and adequate resolution in time and frequency domains. However, vision-based monitoring faces several field challenges and might fail to achieve the required level of working performance in some real-world test conditions (e.g., involving low-contrast patterns and mounting instability of optical sensors). To make the best use of the potential of vision-based systems, a mixed sensing system consisting of a consumer-grade camera and an accelerometer is proposed in this study for accurate displacement measurement. The system considers automatic compensation of camera shake and involves an autonomous data fusion process for noise reduction. The proposed system is demonstrated by a field monitoring test on a short-span railway bridge and is validated to offer higher accuracy and wider frequency range than using a camera alone. Displacement data by the mixed system are demonstrated to be viable for estimating bridge influence line (IL), indicating the potential for bridge condition assessment.

Structural strain responses, generally induced by traffic, wind, temperature, and so forth, can be used to evaluate the safety and serviceability of in-service bridges. According to one-year continuous monitoring of strain data recorded by the structural health monitoring system of the Sutong cable-stayed bridge, the lifetime fatigue reliability of three welded details of the orthotropic steel deck was investigated: rib-to-deck at the diaphragm (RTDD), rib-to-diaphragm (RTD), and diaphragm-to-deck (DTD) details. In this case study, detailed analysis of the separated components of the raw strain data was first conducted and included the slow-varying trend and the dynamic component. The strain variation trend in the bottom flange synchronized with the mean temperature, while that in the top flange did not. In addition, the strain dynamic component was mainly induced by the local vehicle axle loads. In the second step, rainflow counting was used to obtain the stress range histograms, which were then used to calculate the equivalent stress range according to the lognormal-fitting method. Finally, a time-dependent fatigue reliability evaluation of the described three welded details was conducted using one-year monitoring strain data. Results showed that the fatigue performance of the two welded details, RTDD and DTD, remained satisfactory after 100 years of operation because the failure probabilities were both lower than 10⁻⁵. The designed cutout of the diaphragm was applied to the RTD weld at the welded connection between the U rib and diaphragm. This cutout was validated as a means to help achieve better fatigue resistance for the RTD weld. In the future, long-term monitoring strain data (more than 5 years) need to be investigated for better assessment of the fatigue performance of the orthotropic steel deck.