Journal of Bridge Engineering

Although the use of segmental bridge decks has increased around the world, their use in seismic regions under vertical earthquake motions is yet to be fully understood. The asymmetric behavior of segment joints under vertical motions as well as the low strain ductility of cables passing through the joints raise questions on postearthquake performance of decks following a disastrous earthquake and during aftershocks. Because strong aftershocks can expedite the collapse of structures damaged in the mainshock, assessing the residual capacity of mainshock-damaged bridges becomes important with regard to postearthquake performance. In the current research, two medium- and long-span case study bridges were investigated to study the residual capacity of bridges of such type. To this end, a two-dimensional model for segment joints was developed and verified via experimental results. The results related to nonlinear time-history analysis under the design earthquakes showed that midspan segment joints were bound to suffer spalling concretes at the bottom and yielding tendons at the top. The findings revealed that the residual capacity of the mainshock-damaged bridges decreases with the increase in the damage level caused by mainshock, yet not more than 50% in comparison to the intact bridge, even at the worst damage level.

In this study, an adjustment factor was developed to better estimate the shear capacity of simple span prestressed concrete (PC) girders, for intended use in load rating. The adjustment factor is expressed as a function of several critical girder parameters including concrete strength, prestress level, stirrup spacing, and girder height. The adjustment factor was determined from a regression analysis of over 200 shear capacity results. The database was obtained from a parametric analysis conducted with a finite-element model validated with experimental data. Three different code methods were considered for comparison. Generally, code results were found to be inconsistently conservative. Application of the adjustment factor to an established procedure produced improvement in the accuracy and consistency of shear capacity estimation over existing code methods for the range of girder parameters considered. In addition, potential effects on rating factors for inventory and operational levels were quantified.

The combination of continued highway bridge aging and constrained maintenance, repair, and replacement budgets create the pressing need to develop strategies to allocate available management resources most effectively. Strategies for preventative maintenance scheduling and budget projection greatly depend on the ability to predict bridge deterioration. Mechanistic deterioration models, which analyze the physical processes causing deterioration, have the potential to supplement purely statistical deterioration models and to address limitations associated with bridge inspection data and statistical methods. A variety of mechanistic models that consider specific aspects of deterioration processes is available in the literature. This study considered how existing mechanistic models for predicting corrosion-induced cracking of RC bridge decks can be assembled into a comprehensive model that can predict the complete deck service life and be used to propose preventative maintenance schemes for the decks. The construction practices of modern RC bridge decks were investigated and an attempt was made to assemble a mechanistic model, including the effects of epoxy-coated rebar, waterproofing membranes, asphalt overlays, joint deterioration, and deck maintenance. In some cases, new temporary models had to be proposed to fill gaps in existing modeling capabilities. After a complete model was assembled, Monte Carlo simulation with probabilistic model inputs was applied to simulate the inherent randomness associated with deterioration. The results of this effort indicated that mechanistic models are, indeed, promising, and well-timed preventative maintenance may provide longer bridge deck service life with fewer total maintenance actions than current methods do. However, experimental studies of specific deterioration processes and additional bridge data collection are needed to supplement existing models and validate model predictions.

Cable-stayed bridges, of which there are up to 500 around the world, are often the first choice for long-span bridges. As stay cables increase in service life, rust becomes the most common challenge. At present, more than 20 cases of replacing corroded cables are underway worldwide. Inspections of replaced cables prove that corrosion is a leading cause of degradation in the mechanical behavior of cables. However, there is no accurate method of describing the law of degradation of the mechanical behavior of corroded cables and it remains impossible to evaluate the safety of stay cables in a timely fashion. Therefore, this paper reports a study on distribution model of steel wire corrosion, corrosion rate, and mechanical model of corroded cables, establishing governing equations for static configuration and in-plane free vibration of corroded cables. The paper also derives some analytical solutions for both the static and dynamic characteristics of corroded cables. The finite element method is adopted for the simulation and computation of the static and dynamic characteristics of corroded cables to reach, through comparison and analysis of the results of the two methods, the following conclusions. As corrosion time increases, the horizontal cable force of the corroded cable decreases nonlinearly, cable sag increases nonlinearly, and natural frequencies in-plane of the corroded cable present nonlinear reduction. In early corrosion stage, relative change of static and dynamic characteristics of cables is extremely small. For a corrosion time of 12 years, the average cross section area loss rate in cable corrosion region is 30%, but horizontal cable force is only reduced by 1%, cable sag rises only by 1%, and the decrease of each natural frequency in the plane is only 0.54%.

This article presents dynamic tests of three damage-resistant segmental hollow-core bridge columns with posttensioned unbonded strands. One column was constructed without energy dissipaters, whereas the other two columns included different external energy dissipaters. A reference RC column was also investigated. The cross section of the segmental columns was a hollow-core section composed of an outer glass-fiber-reinforced polymer (GFRP) shell, an inner steel tube, and concrete shell cast in between the GFRP shell and the steel tube. The columns combine the advantages of accelerated bridge construction and self-centering as a result of rocking with high energy dissipation from the external energy dissipaters. All columns were subjected to a sequence of scaled near-fault pulse-like ground motions. The well-designed hollow-core segmental column sustained no noticeable damage and no residual drift after a sequence of motions up to 250% of the design earthquake, which caused a peak drift ratio of 8.85%. Conversely, the counterpart conventional column suffered severe damage, with rebar fracture and extensive concrete spalling. The accumulated residual drift of the conventional column was 1.5% after the sequence of motions up to 200% of the design earthquake, which caused a peak drift ratio of 4.8%. The energy dissipated by the segmental columns with external energy dissipaters was comparable to that of the conventional RC column along the tests.

Different from short-span girder bridges, long-span bridges support a large amount of traffic, which significantly influences the dynamic performance of the bridge. The design live load on long-span bridges has seldom been investigated to take into account the dynamic effects from multiple vehicles in traffic flow. The current AASHTO LRFD specification was primarily developed for and calibrated from bridges with spans of 61.0 m (200 ft) or less. Therefore, it is unknown whether it is risky or conservative to use the same design live load from AASHTO on long-span bridges with spans longer than 100 m. Taking advantage of the advanced simulation methodology on the coupled bridge-traffic system developed recently, the live-load effects on a prototype long-span bridge from stochastic traffic flow were comprehensively studied, including the extreme dynamic response and the dynamic amplification factors for different bridge components. To evaluate the applicability of the design live-load in the current AASHTO specification on long-span bridges, the load effects on the prototype long-span bridge were numerically assessed and were compared with the corresponding response envelopes of the bridge under stochastic traffic flow. It was found that the design live load from AASHTO may be unsafe for use as the live load for the design of the bridge girder, pylon, and stay cables for long-span bridges.

Superstructures of highway bridges are load rated regularly as a part of the National Bridge Inspection Standards (NBIS). It is well known that the load-carrying capacity of a superstructure is affected by foundation movements; however, the current load rating framework does not explicitly include these effects. In the current framework, foundation movement could be treated as structural condition change and considered as a permanent load. In this paper, the authors propose an integrated framework for load rating of superstructures and substructures in the presence of continuing foundation movements and geohydraulic hazards. The approach is based on the modification of the load rating equation to include foundation movements and effects of loads other than dead and live loads that can affect the load capacity of a bridge. A methodology for load rating elements loaded in biaxial moment and axial load, commonly experienced by piers, columns, and piles, has also been proposed. The term substructure functionality index (SFI) has been proposed to account for the effect of foundation movement on the functionality of critical elements such as bearings. Applications of the proposed integrated superstructure-substructure load rating and SFI have been demonstrated through two examples of actual bridges. It has been demonstrated that the load rating produced can be nonconservative if the effects of foundation movement are neglected.

This study proposes an alternative and competitive methodology for predicting solitary wave forces on coastal bridge decks using artificial neural networks (ANNs). It is imperative to accurately predict the on-deck wave forces for the design and retrofit of coastal bridges subject to the potential impact of hurricanes and tsunamis. For this purpose, ANNs are used to determine wave loads based on a valid data set. First, the structural, fluid, and wave variables involved in the bridge deck-wave interaction are briefly introduced. The back-propagation network (BPN) wave force prediction model trained using the back-propagation algorithm is highlighted. A data set with 472 evidence cases is prepared based on extensive computational fluid dynamics (CFD) simulations. Three major input variables, the still-water level (SWL), bottom elevation of the girder/superstructure, and wave height, are selected. Then, the procedures of training the ANNs for the vertical and horizontal forces are presented in detail. Finally, the trained network structures with high predictive skills after substantial training are given with a proposed predictive equation for the vertical and horizontal forces. The results showed that the ANN methodology is robust and capable of capturing the underlying physical complexity in the bridge deck-wave interaction.

The three primary bond mechanisms of a 7-wire strand are adhesion, friction, and mechanical interlocking between the concrete surface and the strands’ helical surfaces. Once adhesion fails as a result of micromovements of the strand, it is very difficult to predict the contribution of other two post-initial slip mechanisms to the total bond capacity of the 7-wire strand. The predictions become more difficult when the bond is influenced by the use of oil-based corrosion-protection (OCP) agents. This article discusses the influence of primary bond mechanisms during the loading stages of the posttensioned two-span concrete member and evaluates the contribution of bond mechanisms to the total member resistance and behavior. Elastomagnetic (EM) gauges, which can directly record the force inside the strands during prestressing and loading cycles, were used as one of the primary monitoring mechanisms. Based on these records, it is possible to evaluate force behavior in the strands during successive load stages up to the ultimate limit state (ULS) of the concrete members. The nonlinear bond behavior of the 7-wire strand is presented, including details of its elongation during testing.

Bridge vortex-induced vibration (VIV) involves a number of uncertainties resulting from wind characteristics, structural properties, and bluff-body aerodynamics. Evaluation of VIV considering the variability in the parameter space has been of great concern. In this study, the influence of various parameters related to wind–bridge interactions on the VIV was evaluated based on different reliability calculation approaches. Specifically, the random nature in the parameter space, which was obtained based on the available data from both laboratories and meteorological stations, was propagated to assess its influence on the structural VIV utilizing the second-order second-moment (SOSM), second-order fourth-moment (SOFM), and Monte Carlo simulation (MCS) methods. Three VIV performance functions involving different considerations of vibration-amplitude models and lock-in wind speeds were constructed. A long-span arch bridge was selected as an example to compute the failure probabilities of VIV considering parametric uncertainties and various performance functions.

The steel truss arch is an important structural type for high-speed railway bridges with long spans. The fatigue assessment of rigid hangers under long-term train loads is an important concern. In this study, the Nanjing Dashengguan Bridge, a six-line railway steel arch bridge with three planes of truss arches and the largest span in the world, was taken as a case study. First, a fatigue assessment of one short hanger was carried out based on dynamic strain monitoring data in 2015. The influence of bending behavior, train lane, number of carriages, and train speed on the fatigue performance of the short hanger were investigated. Second, the fatigue damage distribution of full-field hangers induced by a single train was analyzed based on a calibrated finite-element model. The influence of driving direction on the fatigue performance of rigid hangers was discussed. Finally, an engineering approach for fatigue performance assessment of full-field hangers was proposed based on annual train volume. Consequently, it was shown that the bending behavior has considerable influence on the fatigue effects of short hangers. In addition, train lane and driving direction also have a significant influence on the fatigue performance of hangers. The fatigue damage of short hangers in the middle truss arch was the most remarkable, followed by the side truss arch on the downstream side (the Beijing–Shanghai High Speed Railway) and then by the side truss arch on the upstream side (the Shanghai–Wuhan–Chengdu Railway), which should be paid greater attention to in daily maintenance.