Journal of Bridge Engineering

Despite the evidence from past earthquakes and several numerical investigations demonstrating the detrimental impact of vertical ground motions (VGMs) on the integrity of bridge structures, incorporating their effects into seismic assessment and design procedures has traditionally been given limited consideration. Current codes utilize rather simplistic approaches to account for the concurrent effects of vertical and horizontal motions in structural performance evaluations, potentially leading to unconservative estimates of structural demands. This paper reviews the main features of VGMs and their effect on the seismic response of bridges. The methods and empirical models available to estimate vertical motions for design purposes are discussed, and research gaps and related research needs are identified. Finally, the emerging role of physics-based ground-motion simulations, as well as their limitations, in supporting future research and informing the development of simplified design procedures is examined. The main areas of interest for future research are identified in the need to carry out systematic sensitivity studies to gain insight into the main earthquake parameters that influence key VGMs features, understand the influence of soil nonlinearities on VGMs amplitude and frequency content, inform the development of empirical models that cover a range of site conditions and source-to-site distances where current models are poorly constrained, generate arrays of motions to update coherency models to properly inform the analysis of distributed infrastructure, investigate the impulsive character of VGMs, and assess the approximations made in estimating VGMs with 1D site response analyses. Specific focus is laid on large-magnitude earthquakes in the near-field.

The present study focuses on the seismic response of bridges with rocking piers of nonconventional shape, combining the inherent benefits of rocking isolation and accelerated bridge construction. The governing equations of motion of bridge structures with different configurations of piers are derived, including the basic kinematics of the rocking motion, the equation of motion during rocking, as well as the intrinsic energy dissipation mechanisms of impact at the rocking interfaces and on the abutment backwalls. This analytical framework is based on dimensionless parameters that are related to the shape of the piers, and it is shown that the reduction of mass that is achieved with the nonconventional pier configurations leads to: (1) lower restoring effects compared to conventional piers that are rectangular in elevation; and (2) higher rocking stability based on rocking principles. The efficiency of the proposed pier configurations in a bridge with rocking pier isolation is examined for different levels of seismic action, also including earthquakes much stronger than the design earthquake in the area. It is demonstrated that the proposed nonconventional pier configurations can improve the seismic performance of rocking bridges, and at the same time bring benefits related to economic and sustainability aspects associated with a reduction in the use of construction materials.

This study proposes an efficient biobjective cable force optimization strategy for concrete cable-stayed bridges aiming to maximize the safety of the structure under both the serviceability and ultimate limit state required by the design specifications. The multitude of potential load cases within limit states renders cable force optimization approaches challenged to fully satisfy code requirements, leading to encumbered complexity and computational expense. The proposed method utilized a load decoupling approach to separate the effects induced by the cable forces from other load effects to overcome this shortcoming. Furthermore, the relationship between the structural responses and cable forces was established explicitly using the influence matrix method, which aims to eliminate the finite-element method-based structural analysis in the iterations. A practical concrete cable-stayed bridge was utilized to examine the performance of the proposed method. The Pareto optimal fronts yielded by four different multiobjective optimization algorithms show a good agreement with each other, and all the computational time costs by them are less than 50 s for each run. The comparative analysis of different cable stretching plans demonstrates that optimizing the initial stretching cable forces and the final cable forces under the bridge finished state simultaneously can significantly improve the safety of cable-stayed bridges. The results also illustrate that the proposed strategy is a high-efficiency and specification-oriented cable force optimization solution for short-to-medium concrete cable-stayed bridges.

Abstract

In countries similar to Austria, bridges fail due to debris-flow impact on a regular basis. As there is a large uncertainty in terms of the acting forces during these events, this study examines debris-flow impact forces on bridge superstructures. We first set up an idealized load pattern for the load case of debris-flow impact on a bridge superstructure. Second, we conducted 60 experiments in a small-scale physical model (scale 1:30), where we measured debris-flow impact forces on six different bridge profiles in the presence and absence of a bridge pier with two 3-axis force sensors installed at the bridge abutments. Our findings indicate that there is an influence of the superstructure profiles on the magnitude of the effective frontal debris-flow impact force while the presence or absence of a bridge pier affects the direction of the effective frontal impact force, but not necessarily its magnitude. Our results also indicate that the effective frontal impact force acts mainly in the horizontal direction as the vertical proportion is mostly <10%. We found that the forces that act on bridge superstructures are on average between one- and three-fifths of the peak debris-flow force. Our findings can contribute to a better design of bridges against debris-flow impact in the future.

Practical Applications

A debris flow is a mixture of stones, plant parts, soil and other solids, and water that often causes great damage in mountainous regions, as it can transfer very large forces. When debris flows hit bridges, they are often destroyed. Because debris flows are expected to become more frequent due to climate change and therefore more damage to bridges can be expected in the future, it is necessary to gain a better understanding of the impact process of a debris flow on a bridge. Here, we looked at the forces acting on the deck of the bridge. To this end, we have carried out small-scale experiments and systematically investigated the magnitude of occurring forces and how they are influenced by different shapes of the bridge. We found that it makes a difference which bridge profile is impacted and that usually less than half of the total force of the debris flow acts on the deck of the bridge. Our discoveries can help to better construct bridges against debris-flow impact in the future.

The objective of this research is to evaluate numerically and experimentally the cyclic performance of corroded columns constructed with accelerated bridge construction (ABC) methods. Three column-to-footing specimens were built and tested under quasi-static cyclic loads; one specimen was subjected to corrosion with a target 10% mass loss (moderate corrosion), one was subjected to a target 25% mass loss corrosion (severe corrosion), and one served as the control. For the moderately corroded specimen, the accelerated corrosion method resulted in an actual mass loss of 10.5% in the longitudinal steel bars and 18.4% in the steel spiral; for the severely corroded specimen there was an actual mass loss of 24.1% in the longitudinal steel bars and 39.9% in the steel spiral. Increased corrosion caused reduction in column lateral displacement capacity in the cyclic load experiments; the control, moderately corroded, and severely corroded specimens reached a drift ratio of 9.0%, 7.0%, and 6.0%, respectively. Computational models were developed for the control and corroded specimens. Corrosion effects were considered by reducing the cross-sectional area, yield strength, and modulus of elasticity of steel bars; reduction in concrete compressive strength was included due to concrete cracking and reduction of bond. The computational models include bond-slip, intentional debonding, low-cycle fatigue, and buckling. Global and local response comparisons of the numerical models with experiments are carried out. The numerical models show good agreement with the experimental results regarding load and displacement capacity and hysteretic energy dissipation; they are able to capture the main effect of corrosion, which was a reduction in lateral displacement capacity. The computational models were used in parametric studies to examine the lateral force and displacement capacity for a range of corrosion levels.

Multispan bridges with simply supported girders are straightforward to construct and economical but have historically utilized expansion joints between spans. The negative long-term impacts of expansion joints are well-documented in the literature; eventual leaking causes damage to the girder ends and substructures. To avoid this deterioration associated with the use of expansion joints, link slabs may be used instead. However, the complex induced forces and deformations associated with link slabs are not fully understood and may damage the slab, reducing the life of the superstructure. This paper presents the results of a field study examining bonded link slab behavior under ambient (in-service) live and thermal loads on five Texas bridges. Typical Texas link slabs are not debonded at the girder ends, feature continuous longitudinal reinforcement, and incorporate partial-depth precast concrete panels. The five bridges were instrumented with displacement gauges at the girder ends, at both link slab and expansion joint locations, and strain gauges attached to the bottom of the bridge deck. Displacement, strain, and temperature data collected for a period of 1–2 weeks were used to estimate link slab mechanics. The results show differences in behavior between the differing link slab details, lateral deck stiffness characteristics, and continuous deck unit lengths. The increase in superstructure stiffness provided by the link slab is quantified. Longitudinal deck cracking and reinforcing steel yield behavior are predicted at each monitored link slab. The calculated displacement and strain data show that both live and thermal load effects should be considered in the design.

The residual flexural behavior of semilightweight prestressed concrete voided slab girders taken from a decommissioned 28-year-old bridge near Barrhead, Alberta, Canada was investigated. The residual flexural behaviors under loads corresponding to the serviceability limit state (SLS), the ultimate limit state (ULS), and the failure state were evaluated using four-point bending tests. Four girders with different deterioration levels were tested, with one girder exhibiting no visible deterioration considered as the control girder. Material tests on concrete, mild steel reinforcement, and prestressing strands were conducted to better understand girder behavior. Strand corrosion reduced the girder flexural strength by 14%–22% and changed the failure mode from concrete crushing after steel yielding to undesirable strand rupture prior to yielding. However, all girders, regardless of deterioration level, showed satisfactory performance under SLS and ULS loads. The effective prestress force was also studied using digital image correlation (DIC). North American bridge design codes were used to predict the cracking load and flexural strength considering the influence of different corrosion effects. Steel area loss was shown to be the most important factor for both cracking and flexural capacity reduction.

Abstract

Space truss analogy and collapse mechanisms are the theoretical methods which are available at present to predict the collapse loads of single-cell concrete box-girder bridges. It is observed that of the two formulations, the one based on a collapse mechanism is found to be more versatile and better suited to box sections. The eccentric load acting on the top flange of a box girder may be resolved to symmetric and antisymmetric components. The antisymmetric component may again be resolved as torsion component and distortion component. However, no researcher has extended this concept to determine an equation for the estimation of collapse load. The present study proposes a theory for calculating the collapse load of single-cell concrete box-girder bridges considering pure torsion and distortion mechanisms. The box girder is treated as a folded plate structure subjected to the vertical and horizontal components of the load in the plane of each plate. It is assumed that plastic hinges are developed at the four corners of the box girder for distortion mechanism and the cross section causes pure twisting without distortion for torsion mechanism. The proposed pure torsion and distortion mechanisms are incorporated in the existing collapse mechanism method and the modified method is validated with the experimental results available in the literature.

Practical Applications

Estimation of the ultimate load carrying capacity of existing concrete box-girder bridges is discussed in this paper. Among the various simplified theoretical models available to predict the collapse load of single-cell concrete box-girder bridges, the collapse mechanisms theory yields the most accurate results according to the existing literature. To the existing, pure bending and distortion-bending mechanisms, two more mechanisms (torsion and distortion mechanisms) are proposed in the current paper to make the collapse mechanisms theory more conclusive. With the introduction of these two new mechanisms, the collapse load of existing single-cell concrete box-girder bridges subjected to unsymmetrical loading can be predicted by taking the lowest value obtained from: (i) pure bending mechanism; (ii) distortion-bending mechanism; (iii) torsion mechanism; and (iv) distortion mechanism. This will help the bridge engineers to ascertain the functioning of existing as well as new concrete box-girder bridges.

Cable force estimation of the suspenders is of tremendous significance for the safety and condition evaluation of arch bridges. The modern suspender cable structure widely used nowadays calls for an efficient and robust estimation method accounting for the cable bending stiffness, complex boundary conditions, intermediate dampers, and variable suspender segments. To estimate the tension force in arch bridge suspenders, this paper proposes an exact analytical method that can simultaneously consider the aforementioned factors for the first time. Based on a generalized suspender cable model including all these factors, the transcendental equation for cable force calculation was obtained from the determinant of a 4 × 4 matrix derived using the transfer matrix method. Due to the low dimensionality of the matrix, the transcendental equation size is largely reduced. This allows rapid cable force calculation without requiring complicated numerical iteration algorithms. A dimensionless parametric analysis was conducted to investigate the impact of various factors on the frequency parameter of the suspenders. Subsequently, the efficacy of the proposed method was verified, and an extensive estimation error analysis was performed using finite elements. Moreover, the method was applied to four real-world bridges with measured vibration frequency available. The results showed that the method can accurately estimate the tension force in suspenders with flexural rigidity, arbitrary boundary conditions, and any number of intermediate dampers and nonuniform segments. The proposed method can also be used for suspender cable force estimation of other cable-supported bridges, such as suspension bridges.

During hurricanes or typhoons, wave forces acting on low-lying coastal bridges can cause significant damage to their decks. However, current research has paid little attention to the impact of topography on wave forces. This paper aimed to propose an analytical model based on potential flow theory to analyze the impact of topography on wave forces on bridge decks. The model employs the eigenfunction-matching method to solve the boundary value problem of waves acting on bridge decks over a step bottom. The validity of the model was confirmed by comparing it with published hydrodynamic experiment results. We also examined the effect of the truncation order on wave forces and selected a proper truncation order. The wave forces on the bridge deck located ahead or behind the bottom step were calculated. This study examined the water depth, distance from the bottom step to the bridge deck, and coastal boundary on wave forces. The calculated results indicate that the coastal boundary would significantly influence wave forces on bridge decks, especially for long-period incident waves. The wave forces can be mitigated by an optimized configuration of the wave–structure–topography system. This paper contributes to understanding the impact of topography on wave forces acting on bridge decks during extreme wave conditions and provides insights into optimizing the design of coastal bridges. The proposed analytical model can supply preliminary guidance at the initial stage of bridge design without costly numerical simulations or physical model tests.

The experimental performance and numerical analysis of a hybrid two-column bridge bent was examined to evaluate its ability to self-center and dissipate hysteretic energy during earthquakes. The experiment was conducted using quasi-static cyclic loads on a scaled specimen with posttensioning bars for self-centering and stretch length anchors for hysteretic energy dissipation. Posttensioning bars were used to connect the cap beam, columns, and footings without any mild steel reinforcing bars crossing the cap beam-to-column and column-to-footing interfaces. The number of posttensioning bars and initial posttensioning forces and the number of stretch length anchors were determined using mechanics and equivalent design of reinforced concrete columns. No yielding of posttensioning bars, mild steel reinforcing bars, or steel spirals was observed up to a 3.5% drift ratio; yielding occurred only in the stretch length anchors that are replaceable after an earthquake. Several stretch length anchors experienced tensile elongation, which exceeded their diameter. The residual drift of the hybrid bridge bent remained below 0.5% at the maximum applied 3.5% drift ratio without any visible damage to the concrete, steel collars, or steel chairs. A nonlinear numerical model was developed to represent the hysteretic response of the rocking bridge bent and was compared with the experimental results showing acceptable global and local response. The experiment and the nonlinear numerical model demonstrate that the bridge bent remains serviceable after significant drift cycles without any damage requiring repairs, which improves seismic resilience.

Long-span bridges, which are critical nodes of the nation’s infrastructure system, are frequently exposed to extreme hazards, such as flood, scour, hurricane, earthquake, blast, and impact. In spite of their importance, the structural robustness of long-span bridges is not well understood and has not been adequately quantified. Traditional design approaches are unable to provide explicit measures of residual safety of long-span bridges. Current evaluation approaches to ensure safety through redundancy in the event of any localized damage are mainly intended for short- to medium-span bridges. Therefore, a new robustness evaluation approach that is well suited for short-, medium- as well as long-span bridges is proposed. Applicability and versatility of this approach is demonstrated on a three-span I-girder bridge and three long-span cable-supported bridges and the results are compared with those from available approaches. A significant advantage of this approach is its ability to account for and estimate structural robustness corresponding to different user-specified initiating events and different user-specified limit states on a common and unified basis. Thus, unlike existing approaches, our approach can be used as a comprehensive tool to assess the safety of bridges in their intact and damaged conditions to facilitate critical decisions on design and retrofit needs.

As an essential element of a smart city, rapid health assessment of transportation infrastructure, including footbridges, is crucial. This study proposes a method for identifying the frequencies of a footbridge with pedestrians using the vibrations of a shared scooter. To simulate a rider and a scooter, a novel finite-element (FE) model with four degrees of freedom (DOFs) is proposed. One of the key challenges in identifying the frequency of footbridges is the impact of pedestrians, which can result in complex vehicle–footbridge–pedestrian interaction (VFPI) processes. The contact-point (CP) response is further deduced from the 4-DOF model’s accelerations to eliminate its self-frequencies. The influence of road roughness is weakened by employing the residual CP response of the two wheels, which highlights the frequencies of the footbridge. The results indicate that pedestrians can play a “positive” role in indirectly identifying the footbridge’s fundamental frequency even with poor road roughness classes (B and C in this study). The effects of the environmental noise, footbridge damping, and tire damping were examined.

Sliding bearings are a vulnerable component of bridges. Bearing wear will affect the free expansion of the bridge structure and produce greater temperature stress, resulting in damage to the main girder and other components of the bridge. In the process of bridge operation, the timely detection of bearing wear is very important for ensuring structural safety. Therefore, this paper proposes a wear detection method for bridge sliding bearings based on displacement amplitude by eliminating the effects of daily temperature variations. First, the bearing mechanical behavior under temperature effects and the correlation between temperature and bearing friction force are analyzed. The bearing displacement hysteresis model under temperature effects is established, and the variation in thermally induced bearing displacement after wear is obtained. Then, the correlation between temperature and thermally induced bearing displacement is analyzed and, based on the particle swarm optimization (PSO) algorithm and long short-term memory (LSTM) neural network, a multivariate temperature–displacement correlation model is established to achieve the accurate prediction of thermally induced bearing displacement and the elimination of temperature effects. According to the variation in the thermally induced displacement of the bearing after wear, the indicator of thermally induced displacement amplitude errors (TDAE) is proposed, and the cumulative sum (CUSUM) control chart is used to detect the bearing anomaly. Finally, a long-span bridge is analyzed as an example. The results show that the proposed TDAE detection indicator can effectively reflect the sliding friction force of the bridge bearing, and the proposed detection method can accurately detect the sliding bearing wear, which can provide effective information for the bridge caretakers to monitor the occurrence of bearing wear and replace the bearing slide plate in a timely manner.

Abstract

Composite steel bridges in the United Sates are typically constructed using 22 mm-diameter (7/8 in.-diameter) shear studs. The number of shear studs on a girder can be significantly reduced by using larger-diameter studs. This study employed 11 push-out tests to investigate the static performance of 29 mm-diameter (1-1/8 in.-diameter) shear studs. An extensive welding investigation was conducted to develop the optimum welding parameters for 29 mm-diameter studs. Results from experiments showed the static strength of 29 mm-diameter studs satisfied stud strength equations in the AASHTO LRFD Bridge Design Specifications and Eurocode 4. The ductility of the 29 mm studs was comparable or better than that of 22 mm-diameter shear studs. Concrete cracking under service level loading was similar between specimens with 22 and 29 mm studs. Observations indicate that the minimum allowable stud penetration into the concrete deck may need to increase in order for the 29 mm-diameter studs to have good static performance. Using partial-depth precast concrete panels in the bridge deck reduced the static strength of both 22 and 29 mm-diameter shear studs in push-out specimens.

Practical Applications

Efficient steel bridge girder design makes use of a composite action between the concrete deck and the steel girders. Composite action is achieved by welding shear studs to the top flange of the steel girder during fabrication or erection. The number of shear studs needed is directly related to the individual stud strength, which is controlled by the stud diameter. The shear stud diameter most commonly used in steel bridge construction throughout most of the United States is 22 mm. This paper presents laboratory experiments evaluating the static strength of 29 mm-diameter shear studs. The test results showed that 29 mm-diameter shear studs have a static strength that satisfies US bridge design standards. Compared with 22 mm-diameter shear studs, the use of 29 mm-diameter shear studs is estimated to reduce the number of studs needed on a steel bridge girder by 40%. This reduction in the number of shear studs can enhance construction safety, reduce the cost of fabrication, and facilitate the use of partial-depth precast concrete deck panels, which in turn can increase the speed of construction.

Stream-crossing bridges are critical components of the surface transportation system, allowing for the safe and efficient movement of people and goods. However, these bridges may be subjected to extreme hydraulic loading during flood events. To ensure the longevity and functionality of bridges, it is important to evaluate and implement effective countermeasures against hydraulic failure. This study used computational fluid dynamics modeling to quantify the magnitude of hydraulic loading on typical I-girder, box beam, and slab beam bridges in Texas under extreme flow conditions and debris damming and evaluated the efficacy of existing design guidelines for countermeasures (i.e., shear keys and earwalls) meant to resist shear failure of bridges during flood events. Results indicate that the drag force induced by hydraulic loading during a range of annual exceedance probability events (2%–0.2%) can exceed the capacity of a shear key or an earwall, especially for bridges with greater flow blockage area. Flat plate debris damming on the upstream side of the bridge causes a 46% increase in the drag force compared to the no-debris condition, resulting in a force 2.3 times the shear capacity of the shear key. For the cases where the interface shear strength is not sufficient, several approaches are recommended to increase the interface shear capacity: (1) increase the size and/or quantity of the interface shear reinforcement; (2) increase the number of shear keys; and/or (3) increase the length of the bent cap hence the length of the earwall. Findings from this work can inform the development of more robust design criteria for countermeasures to reduce the risk of hydraulic-induced failures at stream-crossing bridges.

Stay cables in cable-stayed bridges are susceptible to vibrations due to their inherent flexibility and low damping. Different countermeasures to control such vibrations have been extensively researched as well as implemented on actual bridges. New techniques for mitigating stay cable vibrations are still needed as longer cable-stayed bridges are being planned and built. External passive/active dampers and crosstied cable networks are the most effective solutions in controlling undesired cable vibrations. Design aids for the selection of passive damper parameters are available for zero, positive, and negative stiffness dampers (ZSDs, PSDs, and NSDs) installed on a single cable. However, the potential of using passive NSDs in a hybrid cable network, which is a combination of crossties and external dampers, has not been explored. This study presents an analytical investigation on the performance of a passive NSD for vibration control in a two-cable hybrid network. It is revealed that in the case of a hybrid network with NSDs, the stability limit of the system is increased as compared with a single negatively damped cable in addition to a significant improvement in system damping without compromising its in-plane stiffness. The influence of major system parameters on the system stability limit and the damping ratio is discussed. The concept of damping contour for a typical hybrid network is adopted to illustrate selection of the required level of damping for a particular combination of damper location and negative stiffness. The effect of negative stiffness on higher modes is investigated and found to be beneficial for the majority of the modes.

Owing to undesired hydraulic effects, bridge collapse accidents have become increasingly frequent during the flooding season. Considering hydraulic effects in bridge design is paramount to controlling and mitigating hydrological damage. Despite the efforts in previous studies on bridges under floods, a proper partial factor of hydraulic effects considering foundation scour is still lacking for bridge design against floods. To bridge the gap, this study proposed an inverse reliability analysis framework to generate a proper partial factor of hydraulic effects and a corresponding partial factor of resistance. First, failure modes of typical short- to medium-span bridges were summarized to construct limit state functions. Then, an inverse reliability analysis framework considering hydraulic effects was proposed. The optimum partial factors of hydraulic effects and corresponding partial factors of resistance were calculated for various design specifications. Finally, a classification early warning system of foundation scour was built to forecast hydraulic failure accurately. This paper reveals the necessity of considering the hydraulic effects of floods in bridge design. The proposed framework and warning system can effectively enhance bridge safety against floods.