Journal of Bridge Engineering

In past decades, the occurrence of catastrophic collapses in post-tensioned concrete (PC) bridges in several countries has raised major concerns about their load-bearing capacity, calling for numerical and experimental studies on the effects of aging, deterioration, and construction defects. In order to investigate the influence of residual prestressing levels and the imperfect grouting of ducts in PC bridges, we undertook an experimental study on the flexural behavior of six PC girders prestressed with two monostrand tendons having a nearly parabolic route. The specimens’ geometry was properly designed based on a 1:5 length scale, assuming a prototype representative of simply supported, beam-type highway bridges in Italy. Two prestress levels were considered as being representative of the expected and defective post-tensioning levels, as observed in several existing bridges. In combination with a different prestressing level, the specimens’ ducts were provided with either full grouting, partial grouting, or no grouting in order to consider the whole range of possible bonding conditions for post-tensioning tendons. The girders were tested in a four-point bending configuration under a quasi-static cyclic protocol up to force-based performance levels, followed by a monotonic loading protocol with displacement control up to failure. The different impacts of the prestress level and grouting condition were addressed in terms of the initial (uncracked) behavior, post-cracking behavior, and ultimate capacity. Limited serviceability was achieved in the case of lower prestressing levels, while a 12% to 15% lower load-bearing capacity was attained in the case of unbonded tendons. In the last section of the paper, an analytical study on the initial stiffness and moment–curvature behavior is discussed in support of the interpretation of the experimental findings.

This study investigates the experimental and analytical torsional behavior of reinforced concrete (RC) bridge box girders reinforced with glass fiber–reinforced polymer (GFRP) bars and continuous spiral stirrups, representing a first in literature. Reinforced concrete box girders were constructed and examined until failure to assess the influence of the spiral pitch and web reinforcement configuration on torsional behavior and strength. The test specimens had continuous GFRP spirals and tie stirrups; the control specimen did not have web reinforcement. The specimens were 4,000 mm long, 380 mm wide, and 380 mm high, and had a wall thickness of 100 mm. The test results demonstrate that the box girder with spiral GFRP reinforcement achieved higher torsional strength and lower twist than its counterpart specimen reinforced with individual GFRP tie stirrups by approximately 6% and 11%, respectively. The specimen with a narrow spiral pitch performed better than the specimens with a wide spiral pitch. An analytical iterative softened membrane model for torsion (SMMT) was used to estimate the entire torsional behavior of box girders with spiral GFRP reinforcement. The analytical results were compared with the experimental results of four bridge box girders with spiral GFRP reinforcement to validate the model's accuracy. The comparison indicates that the model could reasonably predict the cracking and ultimate torsional strength as well as the associated twists.

When the load rating of a bridge is less than 1.0 for AASHTO HL-93 live load and state-specific legal trucks, the bridge is posted. Posting a bridge causes an inconvenience to the public and may result in trucks taking longer routes. Thus, this paper investigated the effects of field-derived distribution factor (DF) and impact factor (IM) from static and dynamic load tests using computer vision and deflection measurements, instead of AASHTO factors, on the bridge load rating and component as well as system reliability for posting avoidance. The reliability approach used Monte Carlo simulations to account for uncertainties in calculating the flexural strength limit state (Strength I). Both Flexural strength I and serviceability (Service III) limit states were investigated. The bridge’s superstructure was studied in as-built, repaired, and damaged condition scenarios. For that, AASHTO HL-93, Florida legal trucks, and emergency vehicles were considered. In this regard, load rating distributions and component and system reliability indices were computed using both AASHTO and field-derived DF and IM. The increase in load rating and reliability was investigated. By using field-derived factors, a load rating increase of up to 17% was achieved. The component reliability also increased significantly. For example, the damaged case’s component reliability increased by 1.0 when replacing DF and IM, which indicates a major reduction in the probability of failure. The increase in system reliability was most significant because using the field-derived DF increased the capacity contribution from other girders. A 2.12 increase in system reliability was achieved in the damaged condition when only substituting DF, providing even higher system reliability as a result of a reduction in the system probability of failure.

A railway pier with a relatively low reinforcement ratio has a high risk of collapse when subjected to an earthquake. The use of a conventional strengthening method of concrete, steel, and fiber-reinforced polymer jackets cannot effectively enhance the deformation capacity of the railway bridge pier, given the relocation of the failure position. This study proposed a novel strengthening device that consisted of L-shaped steel, rubber, stainless steel screws, and high-strength studs and investigated its effect when enhancing the cyclic behavior of a railway pier with a low reinforcement ratio of 0.2%. The experimental results showed that the proposed strengthening device enhanced the initial stiffness, loading capacity, and dissipated energy of the bridge pier without reducing the deformation capacity compared with the unstrengthened pier. The strengthening device and reinforcement were independent components to sustain loading at the failure stage. The contributions of the strengthening device and reinforcement to the total dissipated energy were 40% and 60%, respectively. Their contributions to the loading capacity were 18% and 50%, respectively, and the axial loading provided another 32% contribution. A theoretical formula that considers the contribution of each component to the loading capacity at the failure stage was established, which accurately predicts the mechanical behavior of the pier.

This paper aimed to propose an analytical framework for assessing the postearthquake traffic flow capacity of girder bridges based on the loss model of vertical load-carrying capacity. For this purpose, a loss model of the vertical load-carrying capacity of a reinforced concrete (RC) column associated with the residual drift ratio and the damage level (i.e., the modified Park–Ang index) was developed to determine the postearthquake vertical load-carrying capacity accurately and quantitatively. Subsequently, the probability seismic demand analysis (PSDA) was performed to obtain the probability distribution functions (PDFs) of engineering demand parameters (EDPs) (i.e., the residual drift and the damage indicator) and the PDF of postearthquake vertical load-carrying capacity was determined based on the developed loss model. Furthermore, the reliability analysis was utilized to calculate the postearthquake reliability index of a bridge by adjusting the mean values of the live load (which reflects the traffic flow capacity), and the postearthquake traffic flow capacity could then be quantitatively determined based on the live load ratio at a target reliability index. Finally, the proposed framework was implemented on a single-column bridge to demonstrate its efficiency. Compared to traditional qualitative and subjective postearthquake functionality assessment of the damaged bridge, the proposed analytical approach offered a mathematical model for the decision-making process.

Stud connectors are widely used as shear keys in steel–concrete composite girder bridges, owing to their advantages of easy processing, quick construction, and excellent connection performance. Stud connectors are buried in concrete; therefore, conventional detection methods cannot effectively and reliably detect damage to them. In this study, an acoustic emission (AE)-based methodology was developed to monitor long-term damage to bridge structures and their key components. Damage to stud connectors during the shear failure process was dynamically monitored using the AE technique. AE signals from the entire stud damage process were collected. Subsequently, the characteristic parameters of AE were extracted. According to the process diagram, association graph, and cumulative chart of each characteristic parameter, we first investigated the distributive regularity for the five characteristic AE parameters (energy, ringing count, amplitude, rise time, and duration) of the stud in the elastic, elastic–plastic, plastic, and fracture failure stages. The correlation diagram of amplitude and frequency was also studied. Subsequently, based on the damage factor theory, a damage model of the stud was established by considering the cumulative values of energy and ringing count as the main parameters. The model was further verified using experimental data. More importantly, this proves the feasibility of the model in the quantitative description of the damage process in studs. This study also provides experimental data and a theoretical basis for the detection and evaluation of stud damage in steel–concrete composite girder bridges.

The operational performance of high-speed railway bridges is controlled by stiffness, and the reduction in bridge stiffness leads to a decline in ride comfort. Therefore, it is very important to periodically evaluate the stiffness of high-speed railway bridges. To reasonably evaluate bridge stiffness without operation interference, a high-speed railway bridge stiffness evaluation method is proposed in this paper based on regularly solving the deflection limit and the most unfavorable deflection based on monitoring data. First, the analytical solution of the deflection limit of any bridge that meets the comfort requirements is derived by using the real displacement of the train wheelset. Then, the virtual calculation method of the most unfavorable deflection of the bridge based on the influence line is proposed. The bridge stiffness evaluation is achieved by comparing their periodical calculation results. Finally, the proposed method is verified by the long-term monitoring data of a long-span high-speed railway bridge. The results show that the proposed method can automatically calculate the time-varying curve of the bridge deflection limit and the most unfavorable deflection. Moreover, the evaluation results are intuitive and effective and show the time-varying trend analysis of bridge stiffness. The research results provide a simple and feasible method for the unsupervised stiffness evaluation of high-speed railway bridges.

The traditional design method, with overall factors of safety, is still employed in Chinese specifications for gravity-type anchorages (GTAs) in suspension bridges. In this work, we investigated the safety-margin design method of the GTAs of over-2,000-m-long suspension bridges based on the safety factor and target reliability. The variability features of the design parameters involved in the GTAs are presented. The safety-margin analysis of the GTAs was conducted based on the target reliability and a method of calculation of the corresponding partial factors, and considered sliding and overturning failure. Taking the Zhangjinggao Yangtze River Bridge as an example, the proposed design method was applied to this superlong suspension bridge and the partial factors under different design parameters are discussed. The results showed that the overall factors of safety of the GTAs were decreased by the proposed method, and the construction cost of the GTAs could be greatly reduced. The partial factors of the resistance and load effects are presented, considering the sliding and overturning of the GTAs. The design method proposed, with the suggested partial factors, was finally verified using the GTAs of two superlong-span suspension bridges.

This paper presents a series of strengthening concepts for steel through-girder bridges using ultrahigh-performance concrete (UHPC) and external post-tensioning (PT). Five concepts were investigated either by large-scale proof-of-concept experimental testing or numerical analysis. The goal of the research was to determine the characteristic behavior of the UHPC–steel composite system and provide guidance to designers regarding calculating the elastic and ultimate flexural behaviors of the strengthening concepts. Experimental work included laboratory testing of a single half-scale girder specimen designed using an actual in-service railway bridge as a reference. The half-scale girder specimen was subjected to elastic and ultimate loading. The numerical analysis included the development of a moment–curvature-based flexural capacity model and a limited parametric study. The findings suggest that the strengthening concepts are viable in some circumstances but have some drawbacks such as a need to implement a large UHPC cap with PT to observe increased system capacity. Finally, a brief set of design considerations is provided.

Damage to girders threaten a bridge’s safety. They can be effectively detected by the neutral axis (NA) position of a girder. However, the NA position is inevitably affected by the nonlinear temperature gradient of girders, which could mask the damage-induced abnormality. Aiming at the practicality of the NA position, an improved thermal-varying NA model was scientifically derived by accommodating vertically distributed measurements of a nonlinear temperature gradient, followed by several simplified models. By eliminating the effect of the nonlinear temperature gradient on the NA position to the maximum, an abnormality alarming framework was then established for damage detection of girders. Finally, a girder model imposed by an actual nonlinear temperature gradient was developed to validate the advantages of the improved model and the effectiveness of the alarming framework. The proposed models are an improvement over the existing model in terms of prediction accuracy and stability. Additionally, the NA-based alarming method can effectively detect minor damage to the girder subjected to varying nonlinear temperature gradients. The optimal strain measurement is recommended at the lowest turning point of the temperature difference characteristic above the NA position, and the optimal temperature measurement should effectively represent the statistical outline feature of the temperature difference.

As an innovative steel box girder, the normal stress patterns in the top and bottom plates of a cantilever steel box girder are complex. However, the influence of external and internal struts on the shear lag effect is poorly understood. To address this gap in knowledge, a 1:4.5 scale experimental segmental model was developed. The normal stress patterns in cross sections with and without external diagonal struts under different vehicular and train load cases were studied, and it was found that the vehicle load would result in a large normal stress at the junction of the outer web and top plate and the train load would cause a large normal stress at the junction of the inner web plate and top plate. In addition, compressive and tensile normal stresses appeared simultaneously in the bottom plate under vehicle or train loads, which led to negative and positive shear lag effects in the bottom plate. A bar simulation method was used to explain this phenomenon. In addition, to obtain the normal stress in the cantilever steel box girder, new assumptions about the shear flows that caused the vehicle and train loads in the web plates are presented. Based on the bar simulation method, the influence mechanism of the external and internal struts on the shear lag effect of the cantilever steel box girder was discovered. The external strut limited the shear deformation of the connection zone, which resulted in a small normal stress in the zone. The external and internal struts generated additional shear flow in the bottom plate, resulting in simultaneous compressive and tensile normal stresses in the bottom plate. The results of this study provide a reference for understanding the shear lag effect of cantilever steel box girders in cable-stayed bridges.

Corrosion fatigue is a critical concern in the performance and safety of parallel steel wire cables used in various engineering structures, particularly in bridge applications. This study investigated the complex interaction between tensile, bending, and corrosion effects on parallel steel wire cables and proposed a novel approach to analyze their corrosion fatigue behavior. First, to comprehend the varying corrosion levels and stress distributions along the cables, we introduced the concept of bending characteristic length. Leveraging the spatial fiber bundle model, we accurately simulated the corrosion extent and stress states at different positions within the parallel wire ropes. Furthermore, we conducted comprehensive experimental tests to examine wire breakage behavior in parallel steel wire cables, enabling a thorough validation of our theoretical predictions. The experimental results revealed intriguing deviations between the observed wire breakage sequence and the theoretically predicted order attributed to the influence of eccentric loads and localized variations in wire corrosion. The findings unveiled that parallel steel wire cables in practical bridge structures experience multiaxial corrosion fatigue failure, exhibiting significant variations in corrosion levels and stress distribution along their length. The proposed spatial fiber bundle model exhibited commendable accuracy in predicting wire breakage, with calculated fatigue life closely aligning with experimental observations.

Columns are usually the weak links in conventional bridges with regard to seismic design. Damage of reinforced concrete (RC) columns caused by moderate earthquakes is usually repairable, but significant damage is expected in the event of strong ground shaking. Advanced materials and/or innovative detailing have been developed for RC bridge columns to minimize damage while meeting or exceeding the ductility requirements per current codes. Rocking columns with either internal or external energy dissipators, commonly referred to as hybrid rocking columns, are novel columns with an improved seismic performance. Despite decades of research on rocking columns and promising laboratory findings, they have never been used in any bridge in the United States because of concerns regarding the accessibility and durability of internal tendons, and the lack of system redundancy when tendons are lost. The present study proposes a new class of rocking bridge columns that do not need internal pre- or post-tensioning tendons (or bars). Instead, tendons are placed outside of the column to be fully accessible and replaceable. One half-scale precast bridge column cast with ultrahigh performance concrete (UHPC) was tested twice under the same loading protocol. All external tendons were replaced in the second round of testing to validate repair by the fuse replacement technique. The damage of the precast UHPC column was insignificant throughout testing and retesting. Furthermore, the precast column showed the same displacement capacity, a slightly lower lateral strength, and insignificant residual displacements compared with those of a reference cast-in-place column (CIP). One drawback of the precast column was a lower effective stiffness compared with that of CIP column. A parametric pushover study was performed to investigate the seismic performance of the proposed columns with different fuse materials and lengths and to determine the best fuse configurations for a successful design. Finally, design guidelines were recommended to facilitate future investigations.

Support movements cause nonlinear vibrations in cables, but it is unclear how exactly the cables in cable-stayed bridges respond to the complicated support movements induced by earthquakes. In this study, we employed a displacement approach that separated the cable vibrations into pseudostatic and relative dynamic responses. The former depicted the cable response under static loadings, the latter were caused by the dynamic components of the pseudostatic components. A three-dimensional finite-element model of a cable-stayed bridge was established, with the exact pseudostatic response of the cables included. The cable vibrations were determined following seismic displacements at the cable–deck and cable–tower connections. It was revealed that the cable vibrations were significant both during and after the shaking from the earthquake, and that the maximum response was reached after the shaking in most cases. The longitudinal and vertical seismic inputs mainly cause parametric and in-plane resonant vibrations, whereas the transverse inputs triggered out-of-plane resonant vibrations in the cables. The cable vibrations were more significant when high spectral accelerations of the ground motions occurred in the vibration periods of the cables. It was concluded that the nonlinear cable vibrations should be taken into consideration under larger earthquake conditions.

This case study investigates two of the wind-induced vehicle accidents that occurred on a cable-stayed bridge in Korea over the past 20 years. Both of these incidents happened at the approach deck of the bridge, where the elevation from the sea level was only about 57% of the main span height. The investigation was focused on determining whether specific structural components or geometrical characteristics around the accident locations were responsible for these incidents. To achieve this, scaled-down vehicle and bridge deck models were used in a series of wind-tunnel tests. The results show that the wind load on the vehicles increased by 3–4 times near the accident locations. The primary cause of this anomaly was attributed to the rapid change in deck width. Furthermore, a risk assessment, which considered traffic and wind environments, showed that the risk level at the accident location was 100 times higher than at any other location on the bridge due to these unique characteristics. Additionally, further risk assessment revealed that two measures, traffic control and wind barrier installation, could mitigate the risk at the accident location.

Abstract

The failure of the support system is one of the primary reasons for bridge failures during construction. Existing research on support system failures primarily focused on falsework, with less attention given to other components such as Bailey beams, transverse beams, and steel pipe piles. This study focused on an incident where the support system of a cast-in-situ box girder bridge experienced settlement due to the failure of Bailey beams, transverse beams, and steel pipe piles. To thoroughly analyze the accident's causes, a multiscale elastic–plastic finite-element model of the support system was developed based on the actual on-site layout. By combining the results of the finite-element model with comprehensive on-site data, it was found that the support system settlement accident was caused by a series of construction errors, including the incorrect placement of the Bailey beams, excessive vulnerability in the steel pipe piles' support positions, and inadequate welding strength between the transverse beams. To prevent similar accidents from recurring, the design, construction, and supervisory parties should collectively ensure the consistency between design and construction and increase their attention to potential stress concentrations in certain components of the support system. When the possibility of stress concentration exists, Bailey beams should be reinforced with vertical or diagonal struts depending on their actual support positions, while steel pipe piles should be reinforced with annular steel plates higher than 500 mm.

Practical Applications

This study focuses on an incident where the support system of a cast-in-situ box girder bridge experienced settlement due to the failure of Bailey beams, transverse beams, and steel pipe piles. These failures were primarily caused by inconsistencies between design and construction and a lack of attention to potential stress concentrations in certain components of the support system. In fact, the differences between design and construction are widespread and are one of the primary reasons for the failure of support systems during bridge construction. Therefore, the design, construction, and supervisory parties should work together to reduce the occurrence of such situations. Designers need to identify the most critical assumptions made during calculation and communicate these assumptions clearly to the construction team through a checklist. Construction and supervisory parties should implement these assumptions as much as possible and promptly report when they cannot be met. Furthermore, more attention should be given to potential stress concentrations in the support system. This requires designers to be aware of the limitations of beam element models when analyzing stresses at connection points. When stress concentrations are inevitable, the methods proposed in this study can be used to reinforce Bailey beams and steel pipe piles.