Journal of Bridge Engineering

The configuration of the main girder not only affects the appearance of the bridge, but also directly relates to the mechanical performance of the bridge, which is one of the key objectives for construction control. This paper presents a new geometric-control method (the phase-transformation method) of the self-adaptive unstressed configuration for incrementally launched girder bridges. The phase change of the prefabricated girder (i.e., the relative change of the in-plane horizontal angle and displacement) and the geometric deviation of the assembled segment in the assembly platform are considered in the procedure. First, some basic concepts of the key control parameters are introduced, such as the theoretically unstressed configuration, the reference phase, and the current phase. Next, the coordinate transformations under both the reference and instantaneous phase are derived based on the translation and rotation of the girder's rigid motions. In order to gradually adjust the errors of the unstressed configuration in the assembly process, the unstressed configuration for the already-assembled segments at the reference phase is evaluated, and the unstressed configuration for the ongoing-assembly segments at the instantaneous phase is predicted. Finally, the proposed method is applied and validated in an incremental-launching process of a steel box girder for the Fuyuan Bridge over the Xiangjiang River in China. The predicted configuration of the steel box girder agrees well with the measured configurations; this indicates that the proposed method can effectively evaluate the unstressed configuration for already-assembled segments and can accurately predict the unstressed configuration for the ongoing-assembly segment during the entire incremental-launching process.

A detailed finite-element (FE) modeling procedure is presented for evaluating the redundancy of twin steel box-girder bridges. For this study, it was assumed that the passage of a truck live load triggers the sudden fracture of one girder. Because of the possibility of localized damage in some bridge components, the proposed computational models incorporate material nonlinearity to represent cracking and crushing of concrete and steel yielding. In addition, the proposed FE models are capable of capturing deck haunch separation by adopting a stud connection failure model. This failure mode was first observed during testing of a full-scale bridge that included a girder with a full-depth fracture. Analysis results show that typical twin steel box-girder bridges likely have greater redundancy than the current provisions indicate and that stud connection failure could significantly affect the redundancy of steel box-girder bridges.

This paper investigates the fatigue assessment of existing steel bridges. Measurements can be used to reduce uncertainties in the structural behavior and the effects of action. However, the treatment of the measured response is not clearly defined in today’s codes of practice. A reliability model is suggested that treats the uncertainties for bilinear fatigue endurance and the uncertainties in the measured response. A parametric study on the modeling of the load effect is performed and shows a significant influence on the reliability. The reliability model is used for calibration of the partial safety factors in a deterministic design equation. The suggested partial safety factors enable practical use of measured stresses in the fatigue assessment of existing steel bridges. A numerical example shows the merit of the proposed model and partial safety factors as an increase in fatigue life.

This paper presents a reliability assessment for tie-down cables of cable-stayed bridges subject to negative reactions. The advanced first-order second-moment reliability method (AFOSM) is used to evaluate the reliability indexes. The strength of a tie-down cable and load parameters are selected as random variables. A Newton-type solution scheme with double iteration loops is used to solve the minimization problem defined in the AFOSM. Reactions at supports are calculated through the stiffness equation formed by a finite-element model, and the sensitivities of the reactions with respect to the random variables are obtained by the direct differentiation of the stiffness equation. The reliability indexes of the tie-down cables are evaluated for two cable-stayed bridges in service in Korea: the Second Jindo Grand Bridge and Incheon Grand Bridge. Three limit states on the pretension, required strength, and design strength are considered for the load combination of the Strength I limit state in LRFD bridge design specifications. The required strength is evaluated with the load factors defined in the specifications and the resistance factor recommended for tension members. Design vehicular live load and pedestrian load are applied to the bridges. The reliability indexes and corresponding most probable failure points of the tie-down cables installed in the bridges are presented and discussed in detail. The effects of the partial failure of the tie-down cables and the variation of the resistance factor on the reliability index are investigated.

This paper presents a detailed investigation on numerical simulation of an accidental fire on the Ed Koch Queensboro Bridge, which is a major long-span truss bridge connecting Manhattan to Queens in New York City. A truck traveling on the lower deck of the bridge caught fire, which spread to major bridge components supporting the upper deck. The fire was observed to last approximately 30 min. The heat released from the fire severely damaged two exterior stringers of the upper deck supporting an exterior lane, which led to the closure of this lane for several weeks. This paper presents detailed research on numerical simulation of the entire process of the fire and prediction of the structural response of the deck subjected to the fire loading. The simulation results show very good correlation between the simulated and observed damages, where the simulated out-of-plane deformation of the exposed stringers agrees well with measured deformations. The methodology presented in this paper is an effective approach for fire-structure interaction modeling and simulation and has the potential for application to other civil structures.

Clustering stud shear connectors with minimized spacing based on specifications to form group studs are useful for concrete slab prefabrication and prestress installation efficiency in steel-concrete composite bridges. To date, many long-span composite bridge girders have been designed with wide transverse cantilevers and web spacing, and most of these girders use group studs. The concrete’s self-weight and the weight of moving loads result in a significant transverse bending-induced effect generally consisting of bending stresses and tensile concrete cracks. In this sense, the studs are actually under longitudinal interlayer shear force that is influenced by the transverse bending-induced effect. This biaxial loading effect has not been investigated experimentally. Thus, standard and newly designed push-out tests and corresponding analyses were carried out. In addition, the stud arrangement effect also was of concern. In this study, the ratio of stud height to shank diameter was approximately 6.2. This study found that steel-concrete interlayer friction and biaxial concrete compression around the stud roots contribute to a favorable effect of biaxial loading on stud performance. However, the residual tensile concrete cracks are unfavorable. Engineers should note the tendency toward mechanical degradation of studs when such a situation occurs. Moreover, arranging studs in clusters to form group studs may lead to comparatively more severe concrete damage at the ultimate stage. The specification-based evaluations of stud strength were found to be more or less conservative based on related test results.

In this paper, a three-dimensional nonlinear dynamic analysis framework for RC bridges is established based on the force analogy method (FAM). Two biaxial local plastic mechanisms, rotation hinge (RH) and slide hinge (SH), are proposed based on the fundamental concept of FAM to simulate the nonlinear flexure-shear interactive behavior of RC piers, a critical consideration for seismic performance assessment of RC bridges. The RHs located at the ends of RC piers express the relationships of moment versus plastic rotation, whereas the SHs are assigned to simulate the shear versus plastic shear deformation behaviors of RC piers. Coupling the presented biaxial local plastic mechanisms with FAM, the nonlinear response of RC bridges under bidirectional earthquakes can be evaluated. Because only constant initial stiffness matrices are used throughout the whole analyzing process, the state space integration formulation can be used for solving the equations of motion, which makes the computational process efficient and stable. The precision of the presented biaxial local plastic mechanisms is verified against data of two tests, and a numerical example is carried out to illustrate the process of seismic analysis for RC bridges with FAM.

Structural health monitoring (SHM) systems have been installed in many long-span bridges to assess bridge performance and safety. However, the number of sensors in a SHM system is always limited; therefore, not all of the bridge components can be directly monitored. To facilitate an effective assessment of stress-related bridge performance and safety, a multiscale finite-element (FE) model with detailed geometry and affordable computation time is needed. This paper presents the details of establishing a multiscale model for the Stonecutters Bridge in Hong Kong, which is a cable-stayed bridge with a 1,018-m main span. The twin-box deck of the bridge is modeled with shell elements in detailed geometry such that all stress responses in the bridge deck can be directly computed; other bridge components are modeled using either beam or truss elements. Each segment of the girder is then condensed into a superelement with the substructuring method in order to reduce the number of degrees of freedom. A sensitivity-based model updating is also performed to update the multiscale model with the measured modal frequencies. The comparison between the simulation and test results shows that updating with only modal frequencies can ensure consistency in the dynamic properties between the model and the bridge. Nevertheless, the accuracy in the static displacements and stress responses from the influence line analysis may not be improved by the standard updating process. This indicates a need for multiscale updating techniques that take into account both the dynamic properties and local responses of the multiscale model.

To facilitate an effective assessment of stress-related bridge performance and safety, a baseline multiscale finite-element (FE) model and a corresponding model-updating technique are required so that the FE model can best represent the prototype and can be used to well predict both global and local responses. The companion paper demonstrates that considering modal frequencies alone as updating objectives cannot ensure the updated multiscale FE model being able to predict local (stress) responses accurately. This paper presents a new updating method that uses both modal frequencies and multiscale (displacement and stress) static influence lines as updating objectives. The paper first explains the relationship between displacement influence lines and mode shapes and the relationship between strain influence lines and strain mode shapes. The formulation of the multiscale objective functions and the selection of updating parameters are then presented. As a case study, the proposed model-updating method is finally applied to the multiscale FE model of the Stonecutters Bridge. In light of the large number of degrees of freedom of the multiscale model, the response surface method is adopted in the optimization process to reduce computation time. The updated results show that the proposed model-updating technique can reduce the differences not only between measured and computed modal frequencies but also between measured and computed influence lines.

Infrastructure spending is such a large component of a railroad budget that it must be prioritized to meet the concurrent safety and line capacity requirements. Current bridge inspection and rating practices recommend observing bridge movements under a live load to help assess bridge conditions. However, measuring bridge movements under trains in the field is a challenging task. Even when they are measured, the relationships between bridge displacements and different loads/speeds are generally unknown. The research reported herein shows the effects of known train loadings, speeds, and traffic directions on the magnitude and frequency of displacements as measured on timber pile bents of a Class I railroad bridge. Researchers collected both vertical and transverse (lateral) displacements under revenue service traffic and work trains using LVDTs with a sampling frequency of 100 Hz. To investigate the effect of traffic on timber railroad bridges, displacements were measured under crossing events at different speeds and directions of a test train of known speed and weight provided by the railroad for the field experiment. The results indicate that bridge transverse displacements could help to capture critical changes in timber railroad bridge serviceability (i.e., ability to safely carry out railroad operations) as a function of railroad loading, speed, and direction.

HL-93, the current bridge traffic load model used in the United States is examined here. Weigh-in-motion (WIM) data from 17 sites in 16 states containing 74 million truck records are used to assess the level of consistency in the characteristic load effects (LEs) implied by the HL-93 model. The LEs of positive and negative bending moments and shear force are considered on single- and two-lane same-direction slab and girder bridges with a range of spans. It is found that the ratio of WIM-implied LE to HL-93 LE varies considerably from one LE to another. An alternative model is proposed that achieves improvements in consistency in this ratio for the LEs examined, especially for the single-lane case. The proposed model consists of a uniformly distributed load whose intensity varies with bridge length.

This study proposes a methodology of using small wind turbines for dual purposes, improving the aerodynamic performance of flexible bridges and wind-energy harvesting. A method for the proper placement of small wind turbines on flexible bridges was proposed according to the analogy of conventional aerodynamic appendages. The effectiveness of the proposed method was investigated using the wind-tunnel tests for a bridge girder. It was found from the tests that the wind turbine attached analogously to a fairing was effective for decreasing the vortex-induced vibration of a bridge girder. The optimal spanwise interval of the wind turbines was three times the turbine diameter depending on the distance from the girder edge. The annual energy productions of the wind turbines at the bridge were evaluated from the wind velocity and its probability model at the site. The results of the current study show the general applicability of wind turbines for the improvement of aerodynamic performance and energy supply of flexible bridges, although the capacity of wind-power generation was dependent on the wind characteristics at the bridge site.

The available analytical methods for determining the buckling resistance of trusses typically focus on the local load capacity of individual elements and ignore global in-plane buckling behavior. In addition, theoretical expressions that describe the in-plane critical buckling load of shallow arches do not account for trusses or nonsolid cross sections. This paper investigates the nonlinear elastic in-plane buckling behavior of shallow truss arches subjected to a uniformly distributed gravity load. Adapted methods for calculating the equivalent moment of inertia and equivalent area of truss cross sections are presented first. Using these equivalent geometric properties and existing analytical expressions, a novel methodology is then presented for generating an equivalent arch model that accurately predicts the critical nonlinear elastic in-plane buckling behavior of shallow truss arches. This methodology is validated by obtaining close agreement between the nonlinear elastic critical buckling factors of the truss arches and their accompanying equivalent arch models. Approximation equations, using the equivalent moment of inertia, are also generated for estimating the nonlinear elastic critical buckling factor for fixed- and pin-connected shallow truss arches. A simple strategy is presented to augment the existing nonlinear elastic in-plane arch buckling equations by efficiently identifying the approximate central axis location of the truss cross section at midspan.

The primary objective of this study is to investigate whether simplified blast loading together with a pier-bent model could be employed to reveal the main damage mechanisms of typical highway bridges subjected to blast loading. The high-fidelity finite element model of a pier-bent system for highway bridges was established, and Conventional Weapon Effects (CONWEP) reflected pressure on a rigid surface was applied directly on the structure surfaces. The study shows that the pier-bent model together with the simplified blast loading may reproduce many of the damage mechanisms of typical highway bridges, but simplified blast loading may underestimate the blast-load effects to some extent. A heavier explosive charge than the designed one may therefore be needed in order to capture the full range of damage mechanisms. It is advisable to include an equivalent slab in the model even if the focus is on the column and bent. The study also showed that enhancement of transverse reinforcement significantly improved the blast resistance of highway bridges.