Journal of Bridge Engineering

The findings of an extensive literature survey focusing on bridge structural health monitoring (SHM) deployments are presented. Conventional, maturing, and emerging technologies are reviewed as well as deployment considerations for new SHM endeavors. The lack of published calibration studies (and quantification of uncertainty studies) for new sensors is highlighted as a major concern and area for future research. There are currently very few examples of SHM systems that have clearly provided significant value to the owners of monitored structures. The results of the literature survey are used to propose a categorization system to better assess the potential outcomes of bridge SHM deployments. It is shown that SHM studies can be categorized as one (or a combination) of the following: (1) anomaly detection, (2) sensor deployment studies, (3) model validation, (4) threshold check, and (5) damage detection. The new framework aids engineers specifying monitoring systems to determine what should be measured and why, hence allowing them to better evaluate what value may be delivered to the relevant stakeholders for the monitoring investments.

This paper introduces the durability design of concrete structures in the Hong Kong–Zhuhai–Macau project for a working life of 120 years. The environmental actions are analyzed and the deterioration processes for the structural concrete are identified. The durability design is performed through material composition control and a performance-based procedure. The target design lives and durability limit states are attributed to concrete elements according to their structural importance and maintenanceability. Given the prescriptive requirements on material compositions, the carbonation-induced and chloride-induced corrosions of reinforcement steel are considered as the most critical processes and subject to model-based design. The thickness and quality of concrete covers are determined from carbonation and chloride penetration models using a partial factor scheme. For chloride ingress, the partial factors are calibrated from a full probabilistic approach for a target reliability $\beta =1.3$. The statistical properties of parameters are regressed from 30-year exposure tests. Finally, the study explores the relation between the design values of the chloride diffusion coefficient and the laboratory-measured values to establish a basis for durability quality control in construction.

Active confinement by means of pretensioned steel anchor rods is used for bond strengthening of lap-spliced reinforcement and for improving the seismic performance of wall-type bridge piers. Representative as-built and strengthened pier specimens with lap-spliced reinforcement within the critical hinging region were tested under large drift reversals. The test parameters included ratio of pier longitudinal reinforcement, diameter of the spliced bars, and configuration of the pretensioned steel rods. The strengthened piers developed enhanced bond resistance and low bond degradation of the spliced bars, increases in the lateral load and drift capacities, and much less pinching in the lateral load–drift response when compared with the as-built specimens. In this study, a design approach is developed for engineers to evaluate the active lateral pressure required for adequate bond strengthening and for designing the strengthening system. A design example is provided to illustrate the use of the proposed approach.

The effects of live load in box culverts may be nearly negligible compared with the effects of dead loads when significant fill is placed above the crown of the culvert. The objective of this study was to determine the effects of live load (truck loads) on reinforced concrete box culverts classified as bridges [spans greater than 6 m (20 ft)] under soil fills of different thicknesses. The study considered the field testing of 10 existing reinforced concrete box culverts with fill depths ranging from 0.76 m (2.5 ft) to 4.1 m (13.5 ft). Instrumentation of the culverts consisted of 12 reusable strain transducers and 12 linear variable displacement transducers. The instrumentation was designed to be applied, used, and removed in one day of testing. Loaded trucks were driven over the culvert to provide live load. The results of the testing show that the live-load effect does diminish with increasing fill depth. The 2012 AASHTO LRFD bridge design specifications are overly conservative in predicting strains and displacements compared with the field data for fill depths less than 2.4 m (8 ft). At fill depths beyond about 1.82 m (6 ft), the live-load pressures are less than 10% of the dead-load pressures, and this fill depth may be considered as a point at which live-load effects may be neglected.

In 2009, a joint American Society of Civil Engineers Structural Engineering Institute and American Association of State Highway and Transportation Officials ad hoc group was created to study how current bridge practices could be improved for the future. Among their recommendations was the wider use of nondestructive evaluation (NDE) techniques. Risk-based planning to determine the appropriate inspection frequency, scope, intensity, and methodology would help make the increased time and costs associated with NDE inspections feasible for management budgets. However, a rigorous risk-based approach requires that the accuracy and reliability be quantified for each test. This paper serves as a starting point for quantifying these important variables and identifies the type of information that is still needed. Common NDE techniques were identified, and existing studies were reviewed to identify what data relevant to accuracy and reliability are currently available for these techniques. This review indicates that there is only a limited amount of quantifiable data available for most common NDE techniques for bridges, and not enough to statistically describe the uncertainty.

The girder bridge is one of the most popular bridge types throughout the world. Although much effort has been made to study the impact factor (IF) of simply supported bridges due to vehicle loading, fewer works have been reported on continuous bridges. In addition, most of the previous research on IFs has focused on the bending moment effect, whereas very few studies have focused on the shear effect. In this study, numerical simulations were performed to study the dynamic IFs of both simply supported and continuous bridges due to vehicle loading. IFs for both shear and bending moment were investigated. Some interesting findings were obtained regarding the relationships between the IFs of simply supported and continuous bridges, for both shear and bending moment. These findings can be used as additional references for bridge codes by practicing engineers.

The low stiffness of steel U-shaped girders during incremental launching construction has led to the development of an innovative incremental launching construction method that addresses the special requirements of long, multispan composite bridges. A local stress control strategy is utilized to avoid local yielding of the bottom plate. Analysis of the geometric shape control characteristics of composite bridges located on vertical curves allows a control strategy for launching to be established and validated. The concept of state vector is introduced for geometric shape control and prediction. Field results reveal that most of the elevation errors fall into the range of $\pm 1.0\mathrm{cm}$. This paper demonstrates that highly precise control of geometric shapes can be achieved via the proposed methodology. Through accurate analysis of the geometric shapes of composite bridges, errors can be detected and corrected in a timely manner.

This paper is focused on the development of modular shallow trapezoidal boxes fabricated from cold-bent structural steel plate using standard mill plate widths and thicknesses. This concept was developed by a technical working group within the Short Span Steel Bridge Alliance of the Steel Market Development Institute (a business unit of the American Iron and Steel Institute), led by the current authors. This working group consists of all stakeholders in the steel bridge industry, including mills, fabricators, service centers, industry trade organizations, universities, and bridge owners. The goal of this project was to develop an innovative and economical modular solution for the short-span steel bridge market. Presented is the methodology used for the design of this system, along with experimental validation of the modular composite girder’s flexural capacity. Using experimentally verified analytical methods, the applicability of AASHTO specifications in computing the flexural capacity of the proposed system was assessed. Results of this study show that AASHTO specifications are conservative when used to compute the composite girder’s ultimate capacity. Therefore, a more accurate means of computing the capacity of the proposed system is proposed.

Downslope crosswind bora gusts impacting vehicles represent a significant traffic safety issue, and vehicles on bridges are particularly vulnerable to such crosswinds. Wind tunnel experiments were carried out to investigate the effects of the vertical wind incidence angle and vehicle position on the resulting transient aerodynamic loads. When considering accident risk for the vehicle/infrastructure scenario investigated in this study, the higher risk for vehicles exists at lower vertical wind incidence angles up to 30° and closer to the upwind edge of the bridge deck with respect to steady aerodynamic loads. Shed vortices and wind gusting determined the unsteady aerodynamic loading of a vehicle on the bridge. Effects of shed vortices decreased at larger vertical wind incidence angles, with the wind gusts driving the unsteady aerodynamic loads. Difficulties associated with vehicle maneuvering and stability in the upwind traffic lane in terms of unsteady aerodynamic loading are expected to occur at the wind gusting frequency. Dynamic loading of vehicles in the downwind traffic lanes was due to shed vortices as a consequence of the bridge architecture and aerodynamic form of the vehicle.

This paper presents the major findings of a shake table testing program on a large-scale (1:2.39) novel segmental concrete single-span bridge specimen. Emphasis is given on various specimen configurations and seismic loading conditions. The bridge specimen, termed hybrid sliding–rocking bridge, incorporated a box-girder superstructure with rocking joints and internal unbonded posttensioning (PT), and two single-column piers with internal unbonded PT. The pier columns included end rocking joints and intermediate sliding joints along the column height. Various configurations of the bridge specimen were considered with respect to the seismic mass and the superstructure-to-substructure connectivity. These configurations were subjected to far-field (F-F) and near-fault (N-F) ground motion ensembles scaled to various seismic hazard intensities. Asynchronous support excitation was also considered. The testing program included approximately 145 seismic tests. The dynamic response of the specimen was found to increase with the seismic hazard intensity and the seismic mass. Near-fault motions resulted in larger deformations in comparison to far-field (F-F) motions, particularly in the vertical direction. Asynchronous support excitation resulted in smaller system deformations compared with in-sync shaking. The system residual deformations, including sliding at the column joints, were small.

When tension is applied to steel tendons, they elongate in proportion to the tensile force, as predicted by Hooke’s law. This elongation is used by the South African standard on concrete structural works and the South African standard specification for road and bridgeworks to determine the adequacy of the force applied in a tendon. The standards prescribe an elongation variation limit of $\pm 6\%$ and an average elongation variation limit of $\pm 3\%$. According to these standards, if the elongation variation of the tendon falls outside these prescribed limits, it must be brought to the attention of the engineer. The scatter of tendon elongation results is often greater than the range prescribed by these standards. This usually requires the contractor to retension the tendons at huge financial costs. In most cases, the results obtained after retensioning are the same. This paper analyzes tensioning data obtained from a variety of projects that have been completed in South Africa in recent years. The aim of this investigation is to determine the causes of variation in elongation and suggest adjustments, if any, to the current elongation variation.

Longitudinal diaphragms are frequently used in steel box girders of long-span cable-stayed bridges to obtain desirable performance of steel girders. Field examination, however, reveals that premature cracking may often occur in the diaphragms after only a few years of service. Using the Runyang cable-stayed bridge (RCB) in China as an example, this paper presents an investigation of the cracking damage of longitudinal diaphragms, in which the pattern, location, and propagation of cracks are evaluated according to nondestructive field tests. To further look into the failure mechanism, a multiscale finite-element (FE) model of the RCB is developed, and the influence of diaphragms on local and global behavior of the bridge is investigated. In conjunction with a comprehensive vehicle load model developed using traffic information from a toll station, probabilistic FE analyses are performed, and the predicted fatigue lives of specific details are obtained and compared with those in field examination, where good agreement is observed.

Much research has been conducted to study the dynamic impact of simply supported bridges due to vehicles moving at constant speeds, whereas only a few studies have focused on the impact due to vehicles changing speed on bridges. Previous numerical studies have shown that the impact factors due to vehicle braking may exceed those prescribed in the bridge design codes. However, most researchers adopted simple vehicle and bridge models that were not able to consider the spatial effect of real bridges and may have overestimated the actual impact factors due to vehicle braking. In this study, a three-dimensional vehicle–bridge coupled model was developed to study the dynamic impact factors of simply supported prestressed concrete girder bridges due to vehicle braking. Impact factors for different bridge responses were studied, including deflection, bending moment, and shear. The results showed that the impact factors due to vehicle braking could be notably larger than those due to the vehicles moving at constant speeds and could exceed the impact factor specified in the AASHTO bridge design code.

For external tendon members subjected to sustained loads, the time-dependent effects resulting from concrete creep, shrinkage, and tendon relaxation would interact with the second-order effects resulting from the change in tendon eccentricities with the development of time-dependent deformations. This interaction should be adequately considered in a time-dependent analysis of this type of member. This paper presents a numerical model developed to predict the long-term behavior of externally prestressed concrete members at service conditions, taking into account the interaction between time-dependent and second-order effects. The proposed method of analysis is verified with the available experimental results. The time-dependent behavior of externally prestressed concrete members is evaluated, focusing on the effect of deviators and nonprestressed steel. The results demonstrate that the second-order effects result in significant changes in long-term responses other than the prestress loss. The effect of bottom nonprestressed steel on the long-term behavior is found to be limited, whereas the effect of top nonprestressed steel is very important.