Journal of Bridge Engineering

Seismic isolation is a commonly adopted approach for designing bridges against earthquakes. However, the period elongation in an isolated bridge will generally lead to a large superstructure displacement, which may result in pounding, bearing unseating, or even span collapse. This study focuses on the implementation of energy dissipation devices for retrofitting an existing bridge isolated by lead rubber bearings (LRBs). Four different retrofit measures, namely yielding steel cables (YSCs), viscous dampers (VDs), friction dampers (FDs), and superelastic shape memory alloy cables (SMAs) were considered in this study. Fragility analyses were performed to evaluate the relative effectiveness of these devices in minimizing the seismic vulnerability of the bridge. The results indicate that all the devices show comparable performance in reducing the probability of damage of the isolation bearings without imposing much additional vulnerability on the bridge piers. The SMAs are the most effective in mitigating the seismic vulnerability of the bridge system at all the damage states, followed by FDs, VDs, and YSCs. Due to the superior self-centering capacity, the SMAs retrofitted bridge exhibits better recentering performance with a reduced residual displacement of superstructure compared with the bridges with other retrofit measures.

Reinforced concrete four-pile caps under wall loading occur in heavily loaded foundations in bridge construction. The failure mode of shear across the full width of the cap may occur in these deep structural elements. A statically determinate two-way grillage model, comprising orthogonal deep beam grillage elements obeying a predetermined test observing deflection pattern and boundary conditions, is established to solve the structure’s shear capacity. The model gives more accurate and faster solutions than the traditional strut-and-tie method and commercial nonlinear numerical modeling. A key step to solving the model is a linear constitutive (load-deflection) relationship developed for the grillage elements. The grillage model is verified against laboratory experiments for nine pile caps at the University of Southampton (UoS) with the results of a numerical modeling parametric study. A Visual Basic Userform-based design software is developed, incorporating the model and enabling engineers to obtain the shear capacity, full-field reinforcement stress distribution, and cap deflections within seconds.

Self-suction-and-jet flow control is a passive flow control method involving self-organized suction at the leading edge and a wake jet at the trailing edge of a structure. In this study, it was used in a 1:125 physical model of the Great Belt East Bridge to decrease dynamic wind loads and modify the flow structure around the main girder. Experiments were performed in a wind tunnel at a wind speed of 12 m/s, yielding a Reynolds number of 2.8 × 10⁴ for the height of the main girder model. The surface pressure (and therefore, the aerodynamic force) fluctuated less in the controlled models than in the uncontrolled model. The velocimetry data indicated that self-suction-and-jet flow control effectively changed the vortex shedding process in the wake of the model. The interactions between the self-organized jet flows and shear flows caused the trailing edge vortex shedding to transform from asymmetric to symmetric, eliminating the vortex shedding completely. Linear stability analysis of the mean wake flow structures indicated that self-suction-and-jet flow control pushed the unstable flow region farther downstream.

Pretensioned concrete elements are commonly fabricated with strands 12.7 or 15.2 mm (0.5 or 0.6 in.) in diameter; however, the industry has seen interest in using larger-diameter strands in recent years. The use of larger-diameter strands results in greater transverse tensile stresses within the girder end regions, which may increase cracking at the time of prestress transfer. Such cracks may continue to grow during service and cause durability concerns. Moreover, increased damage around the strands and at the web–flange interfaces may lead to unconventional failure mechanisms, such as anchorage-induced or horizontal shear failures. This paper introduces a modeling approach for investigating the performance of pretensioned girders fabricated with strands 17.8 mm (0.7 in.) in diameter from prestress transfer until failure under shear-critical loading. Data from seven full-scale prestress transfer tests and 10 load tests showed that the model can capture the transfer lengths, end-region stresses, and cracking at prestress transfer as well as load-deflection response and failure modes. Subsequently, three remedial end-region reinforcement details were investigated using the validated approach to examine their efficacy in controlling end-region cracks and stresses.

Collision of vehicles into RC bridge columns can result in significant damage to individual bridge components, leading to partial or full collapse of the entire bridge. Among various alternatives to RC columns, concrete-filled steel tubes (CFSTs) have received growing attention because of their rapid construction, reduced labor requirement, and reasonable material cost. Despite the promise of this alternative, however, there is a gap in the existing literature concerning the measures that can be used for the analysis and design of this important category of bridge columns subjected to impact loads. To address this gap, a detailed investigation is conducted in the current study, using a set of impact simulations. For this purpose, representative finite-element (FE) models are developed and validated with the experimental test results. To make a direct comparison possible, the numerical simulations include both CFST and RC columns under a range of vehicle impact scenarios. The structural performance is evaluated using a comprehensive set of measures, including peak dynamic force (PDF) and equivalent static force (ESF). On establishing the necessary metrics, the current study provides a systematic effort to examine the contribution of the main analysis and design parameters to the impact response of the columns under consideration. Based on the simulation results, the sufficiency of the current specifications is evaluated, and a generalized equation is proposed to predict the ESF for CFST columns.

Regular bridge inspections are key to maintaining healthy infrastructure and to preventing unanticipated structural failures. In recent years, mobile inspection robots have been proposed as a tool to aid bridge inspections. Their key advantages include the ability to access areas of a bridge that are otherwise difficult to inspect and the ability to automate the process of collecting and processing data to increase repeatability and reliability of inspections. Although software algorithms have successfully demonstrated the ability to automate defect detection, many data collection platforms, such as drones and ground vehicles, still require an operator to control the robot via teleoperation, and they do not adequately address the challenges associated with automating data collection for bridge inspection, which is central to achieve repeatability of inspections over time. In this study, the challenges associated with automating data collection for visual inspection of bridges are addressed using a ground-based robot, and an autonomy framework, which can meet the requirements for management and execution of inspection plans, is presented. Key tasks considered in this study are managing inspection plan execution on a ground-based robot, robot localization and mapping, and autonomous navigation in a bridge environment. This automated data collection framework is demonstrated on a concrete bridge by automatically building an accurate point cloud reconstruction of the bridge. Automating data collection can enable more systematic and repeatable inspections, which is a critical upstream task to constructing deterioration models in structural components using inspection data collected over the lifetime of a bridge.

The seismic performance of prefabricated segmental bridge columns (PSBCs) with ultrahigh-performance fiber-reinforced concrete (UHPFRC) bottom segments was investigated through model tests and numerical simulations in this study. Four large-scale PSBC specimens with different bottom segments were designed and tested under cyclic quasi-static loading. A novel bottom segment construction, combining a RC cast-in-place inner column and an UHPFRC external precast hollow column, was proposed to improve the energy dissipation capacity of the PSBCs. Seismic behaviors of the test specimens, including the damage pattern, hysteretic characteristics, residual displacement, joint opening, and energy dissipation capacity, were investigated. It was found that the PSBC specimens with UHPFRC bottom segments had greater lateral capacity and residual displacements than those of the specimen with the RC bottom segment, and the former exhibited minor concrete damage during the tests. The PSBC specimen with the composite bottom segment showed greater energy dissipation than other specimens, at relatively high drift levels. Detailed finite-element (FE) models were developed to predict the cyclic behavior of the PSBCs with UHPFRC bottom segments. Good agreements were observed between the FE results and the experimental results, indicating the applicability of the developed FE models. Based on the validated FE mdoels, parametric analyses were conducted to explore seismic behaviors of PSBCs with different hollow ratios and height ratios for the bottom segments. Analytical results indicated that the hollow ratio of UHPFRC bottom segments had a limited influence on the lateral capacity of the PSBC models, and the PSBC model with the bottom UHPFRC segment having a hollow ratio of 0.5 exhibited greater energy dissipation capacity. The lateral capacity and energy dissipation capacity of the PSBC models with the composite bottom segment were improved with the increase of bottom segment height, up to a 0.375 height ratio.

This paper presents an experimental research work to determine temperature gradients in concrete bridge girders under natural environmental conditions. Three AASHTO Type I-girders having different configurations (with and without wide top flanges) were considered in the experimental program. Temperature was monitored in the bridge girders to determine the vertical and transverse temperature gradients in a predeck placement condition. It was found that uneven heating of optimized bridge girder sections results in large nonlinear temperature gradients. The current AASHTO design standard, which only uses a nonlinear vertical but no transversal temperature gradient, was found inaccurate to predict both shape and magnitude of temperature gradients for the analyzed girders.

This study investigates the mechanical properties of ASTM A1010 steel plates and assesses their cost efficiency through life cycle cost (LCC) analyses when used in bridge construction. First, tensile tests were conducted on specimens with different plate thicknesses and rolling direction orientations. The overall stress–strain response and tensile properties of the A1010 steel were evaluated. In addition, failure zones of fractured specimens were analyzed using a scanning electron microscope to reveal the fracture morphology and failure type. Then, to assess the competitiveness of this relatively new steel in bridge construction, a series of LCC analyses were conducted. The first analytical investigation focused on the comparative LCC performance of two case study bridges located at different atmospheric environments and constructed using either A1010 steel or painted conventional carbon steel. The second analytical study explored the major factors impacting the A1010 payoff time. Results indicated that the use of A1010 steel can be most beneficial in bridges located in aggressive environmental conditions with heavy traffic volumes.

During bridge construction, the flexible support conditions provided to precast, prestressed concrete girders by steel reinforced neoprene bearing pads allow for a rolling motion about an axis parallel to the span of the girders and may lead to girder instability. Imposed skew and/or slope angles significantly reduce the roll stiffness of bearing pads, which reduces the ultimate buckling capacity of the girders under the gravity loading condition. In this paper, roll stiffnesses for bearing pads under skew and slope conditions are derived from experimental data gathered from a test device designed to measure such values. The test device reproduces the forces acting on a bearing pad in the field while simultaneously permitting axial load, skew angle, and slope angle to be controlled independently, isolating the influence that each parameter has on bearing pad roll stiffness. A total of 108 tests were performed on three different standard bearing pads, with varying severity of imposed skew and slope angle.

Rocking piers can limit the seismic damage and residual displacement under strong earthquakes to maintain the post-earthquake serviceability of bridges. This article presents an experimental study on the seismic response and rocking isolation of a bridge with post-tensioned rocking piers exhibiting negative rocking stiffness. A 1/10 scaled single-span bridge was precast and tested on a shaking table. The experimental results show that appropriately designed unbonded tendons can enhance the seismic stability of rocking bridges without serious loss of isolation efficiency. The bridge model presented excellent post-earthquake resilience with negligible residual displacement and damage due to enhanced rocking interfaces. In addition, a larger section depth of the columns rendered ample stability but weaker isolation efficiency.

With the increasing demand in freight transportation, truck overloading has become a common issue worldwide. Overloaded trucks pose great challenges for transportation administration in that they can jeopardize the safety of bridges and even lead to bridge collapse. Traditionally, vehicle-induced damage on bridges was estimated based on the line-girder analysis, as suggested by bridge design codes. These analysis methods have been criticized to overly underestimate the bridge capacity. In this study, the fatigue damage (FD) of a typical composite girder bridge under truck overloading was investigated using the OpenSEES framework. The bridge system was regarded as a series-parallel system composed of concrete deck slab and a steel girder subsystem. A method for determining rational vehicle weight limits for highway bridges to achieve the desired service life was proposed considering the FD of bridges. The proposed method could also be used for estimating the FD of bridges caused by truck overloading. Numerical simulation results obtained from this study have shown that the cumulative FD of bridges under severe overloading conditions could increase rapidly, and it may threaten the safety of bridges, which underscores the importance of enforcing truck weight regulations on highway bridges.

This article presents a numerical study on the behavior of hollow-core fiber-reinforced polymer–concrete–steel (HC-FCS) columns under combined axial compression and lateral loadings. The investigated HC-FCS columns consisted of an outer circular fiber-reinforced polymer (FRP) tube, an inner square steel tube, and a concrete wall between them. The HC-FCS column has several advantages over RC columns. The tubes act a stay-in-place formwork, providing continuous confinement and reinforcement. The concrete shell prevents the outward buckling of the steel tube, which improves the column strength. Three-dimensional (3D) numerical models were developed and validated against experimental results. The models subsequently were used to conduct a parametric finite-element (FE) study investigating the effects of the concrete wall thickness, steel tube width-to-thickness (B/t_s) ratio, confinement ratio, concrete strength, applied axial load level, and buckling instabilities on the behavior of the HC-FCS columns, with a particular emphasis on local buckling of the inner tube. This study revealed that the behavior of HC-FCS columns is complicated due to the interaction of the stiffness of the three different materials: concrete, steel, and FRP. In general, in the HC-FCS columns with square steel tubes, failure was triggered by local buckling of the steel tube followed by FRP rupture. The presence of the concrete wall restrained by the outer FRP and inner steel tubes significantly affected the steel tube buckling. Expressions were also developed to predict the local buckling stresses and strains of the square steel tube.

This paper describes the residual strength of damaged strand and wires from protected cable stay bundles subjected to severe blast qualification tests. This effort was motivated by the question: What reserve strength is available, if any, in damaged strands and wires from protected cable stay bundles surviving a blast test? This question arises from performance requirements to evaluate the adequacy of protection mitigation measures for cable stay bundles. To address this question, selected strands and wires from cable stay bundles had their damage characterized and were tested in tension, and then their tension capacity was compared with that of undamaged strands or wires. Testing revealed cold work of the strands from the blast reduces the residual strength by a mean value of 5% and, based on these results, it is recommended to apply a strength reduction factor of 0.95 to all intact or non-severed wires in a cable stay bundle for future blast qualification tests.

Reliability-based design optimization (RBDO) is frequently used to determine optimal structural geometry and material characteristics that can best meet performance goals while considering uncertainties. In this study, the effectiveness of RBDO to develop a load rating model for a set of bridge structures was explored, as well as the use of an alternate best selection procedure that requires substantially less computational effort. The specific problem investigated was the development of a vehicular load model for use in bridge rating, where the objective of the optimization is to minimize the variation in reliability index across different girder types and bridge geometries. Moment and shear limit states were considered, where girder resistance and load random variables were included in the reliability analysis. It was found that the proposed best selection approach could be used to develop a rating model nearly as effective as an ideal RBDO solution but with significantly less computational effort. Both approaches significantly reduced the range and coefficient of variation of the reliability index among the bridge cases considered.

Investigations on the wind loads and aerodynamic responses of the bridge girder segment during the lifting construction stage are limited. Free vibration tests of a lifting girder segment of a kilometer-span cable-stayed bridge were carried out in a wind tunnel to study its aerodynamic performance. Large aerostatic displacements were observed in the wind velocity range of concern. Large-amplitude limit cycle oscillations (LCOs) around the horizontal axis perpendicular to the bridge span occurred when the full-scale velocity exceeded 25.3 m/s. The analytical expression of the eigenfrequency of the dangerous mode of a lifting girder segment was derived, and the analytical result was compared with those determined by using the finite-element analysis (FEA) and testing results. The characteristics of the large-amplitude LCOs under different conditions were thoroughly analyzed. For various testing cases, the influences of the angle of attack, wind velocity, and vibration amplitude on the vibration frequency and aerodynamic damping ratio were comprehensively investigated and the parameter identification accuracies were verified. It was demonstrated that more attention should be paid to assessing the wind-resistance of lifting girder segments to ensure the construction safety of long-span bridges. The results of the present work can provide beneficial reference for evaluating the wind-resistance performances of similar types of lifting girder segments.

The bridge influence line is an important tool to study the bridge response under moving loads and contains tremendous structural information. Structural deterioration during the bridge’s service life will induce variation in the bridge influence line, which makes it essential to identify the influence line exactly from the field measurement data under moving vehicle loads. This article establishes the underdetermined influence line identification model for a bridge under multiaxle vehicle excitation, in which the bridge influence line is identified based on the regularized least-squares QR decomposition method. Then an example of a four-span girder bridge is provided to prove the validity of the method, and the accuracy and computational complexity of different methods in this condition are compared. This study thus provides an effective method for the identification of the bridge influence line with very high computational efficiency and identification accuracy.

This study investigates the parameters design of the tuned mass damper (TMD) for mitigating the vortex-induced vibration (VIV) of long-span bridges, which includes the selection of vortex-induced force models and robustness problem. The critical damping ratio of the bridge obtained by wind tunnel tests is used as the control objective of the TMD for VIV mitigation. Two types of optimum design parameters of the TMD and equivalent damping ratios contributed by the TMD based on empirical linear and nonlinear models are discussed and compared. A flatness for the equivalent damping ratio curve versus system error is used to quantify the robustness of the TMD, and consequently a simplified formula for the optimum damping ratio of the TMD is given based on the flatness. The VIV mitigation of the Hong Kong–Zhuhai–Macao Bridge (HZMB) deep-water nonnavigable bridge is used to illustrate the parameters design of the TMD. The results show that the empirical linear model gives a conservative control evaluation and large damping ratio of the TMD compared to the empirical nonlinear model, and these differences result from their different controlled frequencies in the VIV mitigation. The flatness can both quantify the result of mistuning phenomenon of the TMD and consider its probability of occurrence. The proposed simplified formula avoids the difficulty in selecting the damping ratio of the TMD in the VIV mitigation of bridges. The frequency ratio and damping ratio of the TMD for the HZMB deep-water nonnavigable bridge are initially taken as 0.996% and 5.57% under the given mass ratio of 0.36%. The result of fatigue tests shows that the manufactured TMDs have sufficient performance stability on the VIV mitigation of the HZMB.