Journal of Bridge Engineering

Bridge load testing can answer a variety of questions about bridge behavior that cannot be answered otherwise. The current governing codes and guidelines for bridge load testing in the United States are the 1998 NCHRP Manual for Bridge Rating through Load Testing and Chapter 8 of the AASHTO Manual for Bridge Evaluation. Over the last two decades, the practice of load testing has evolved, and its intersections with other fields have expanded. The outcomes of load tests have been used to keep bridges open cost-effectively without unnecessarily restricting legal loads, when theoretical analyses cannot yield insights representative of in-service performance. Load testing data can be further used to develop field-verified finite-element models of tested bridges to understand these structures better. In addition, structural reliability concepts can be used to estimate the probability of failure based on the results of load tests, and noncontact measurement techniques capturing large surfaces of bridges allow for better monitoring of structural responses. Given these developments, a new Transportation Research Board (TRB) Circular, Primer on Bridge Load Testing, has been developed. This document contains new proposals for interpreting the results of diagnostic load tests, loading protocols, and the determination of bridge load ratings based on the results of proof load tests. In addition, included provisions provide an estimation of the resulting reliability index and the remaining service life of a bridge based on load testing results. The benefit of load testing is illustrated based on a cost–benefit analysis. The current state-of-the-practice has demonstrated that load testing is an effective means for answering many important questions regarding bridge behavior that are critical to decisions on bridge maintenance or replacement. Load testing has evolved over its history, and the newly developed TRB Circular reflects this evolution in a practical way.

Due to the superior performance of negative stiffness damper (NSD), its application to the vibration control of bridge stay cables attracts much research attention in recent years. In the current study, an experimental study on the dynamic response of a cable-NSD system is conducted to investigate the effect of negative damper stiffness and damper support stiffness on the efficiency of NSD. In particular, the impact of the latter, which was only reported in a recent analytical study, will be verified in the lab. A numerical simulation is performed to not only validate the experimental results, but also provide a comprehensive evaluation on the influence of various system parameters on NSD performance. An NSD design tool is developed to predict optimum damper size and the corresponding maximum achievable modal damping ratio of a cable-NSD system. Results show that when the stability criterion is satisfied, choosing stronger negative damper stiffness would enhance NSD efficiency. The impact of support stiffness on NSD performance depends on the magnitude of damper stiffness. Attach an NSD to a cable having larger sag and/or higher bending stiffness would yield a lower maximum achievable system modal damping ratio.

The perceived and observed differences in the dynamic behavior between wheeled and tracked military vehicles should be accounted for in the application of appropriate dynamic load effect values for bridge design and assessment. No current North American bridge design or assessment code provides guidance on methods to differentiate between the dynamic loading effects of wheeled and tracked vehicles. Civilian codes and the Military Load Classification (MLC) system used by the North Atlantic Treaty Organization (NATO) typically use the same dynamic loading effects values for both wheeled and tracked vehicles that can significantly impact and limit the mobility of tracked vehicles. Bridge load testing was carried out to compare the dynamic loading effects between three wheeled military vehicles and a main battle tank, Leopard 2. Results indicate that it may be appropriate to reduce the dynamic load allowance (DLA) used for military tracked vehicles by one-third of that used for military wheeled vehicle analysis. A review of several nations' DLA values was carried out, and application of a reduced DLA for tracked vehicles could result in an increase to the predicted bridge capacity of 5%–13% for tracked vehicles.

Due to the complex clay–pile interaction and significant amplification effect of soft clay, the seismic performance of the piled bridge in soft clay ground is largely unassured. In this study, a suite of both parametric and fragility analyses was performed to investigate the seismic performance of piled pier systems installed in soft clays, in which a validated hyperbolic–hysteretic model and an equivalent elastic–perfectly plastic model were employed to depict the dynamic behaviors of the clay and pile–pier system, respectively. The clay–pile–pier systems were found to be effectively influenced by the factors, namely, ground motion intensity, bridge girder mass, and pile flexural rigidity, to varying extents. The seismic response of the pile was comparatively more complex, which was generally nonlinear against each of the factors considered and predominantly influenced by the kinematic effects induced by the surrounding clays. Furthermore, the maximum curvature response was found to be more applicable to describing the evolving damage states of the pile–pier systems under seismic shakings. Subsequently, a total of four different damage states of the pile–pier system were quantified in terms of the curvature ductility, and the plots of probability of the clay–pile–pier system exceeding one specific damage stage against the ground motion intensity were obtained from the fragility analyses.

A reliable pedestrian load model is a prerequisite for the accurate calculation of human-induced structural vibration. In recent years, many researchers have proposed pedestrian load models based on direct force measurements, such as force plates. However, direct measurement techniques often suffer from incapability when applied to real structures in operation and can hardly be used to measure crowd loads. In this paper, an inverse load identification method is proposed to extract pedestrian vertical load from structural responses. Through a genetic algorithm, the pedestrian’s pacing frequency, dynamic load factors, and phase angles in the Fourier-series model are identified from structural acceleration responses. The proposed algorithm is further investigated for the identification of multiple-pedestrian load parameters, where structural displacement responses are used to give an equivalent number of pedestrians. Numerical examples demonstrate that the pedestrian load parameters are estimated with high accuracy and robustness against noise and modeling errors. A sensitivity analysis is given to explain the different estimation accuracies among the parameters. Finally, the proposed method is validated through an experimental test, showing its practicality for identifying pedestrian loads in real structures.

Concrete adjacent box girders are widely used in short- and medium-span highway bridges. Effects of bridge accessories, such as curbs and parapets, on the structural performance are commonly ignored in design, health monitoring, and evaluation. The standard practice is to provide expansion joints in the parapet wall for reasons of temperature differentials, shrinkage, and settlement. Lack of knowledge on the influence of expansion joints in bridge accessories may have serious consequences in engineering practice. The Yangsi Highway Bridge located in Zhejiang, China, experienced extensive L-Type cracking on the edges of the exterior box girders concentrated below the expansion joints. In order to investigate the observed phenomena, 3D finite-element models were developed to investigate the relationship between the L-Type cracking and the presence of the expansion joint. Significant stress concentration was observed at the edge of the exterior box girder below the expansion joint. The analysis revealed a unique cracking mechanism based on the consistent deflection response and was validated with experimental tests. Parametric analyses were finally conducted to provide important insights into the factors that influence the stress concentration.

A new short-span highway bridge system composed of inverted steel tee sections embedded in a concrete deck slab was developed for the Pennsylvania Department of Transportation. The interface shear connection between the concrete deck slab and steel tee sections is nontraditional and is fabricated by drilling holes near the top of the steel tee stems, placing transverse reinforcement bars through the holes, and casting the top of the steel tee stem into the deck. This paper discusses the mechanism and design of this interface shear connection between the concrete deck and the steel tee section to create composite action. The research approach is based on push-out tests conducted on full-scale subassemblies and validated with destructive tests on a full-scale prototype bridge module. The test program and the resulting design equations are discussed. The test results indicate that the response of this interface shear connection between the concrete deck and the steel tee section is dominated by shear yielding of the reinforcement bars passing through the holes in the tee section stem. After shear yielding of the bars, there is local crushing of the concrete and strength recovery as the bars develop catenary action. At larger relative deformation between the deck and steel tee (shear slip), a concrete breakout failure occurs on the bottom of the concrete deck. The use of a stem hole with no bar creates a brittle concrete shear dowel; the strength of this dowel can be estimated using a concrete shear strength formulation. Because the concrete dowels are brittle and the reinforcement bars passing through the stem holes have a ductile response, the recommended interface shear connection utilizes bars in all holes. The results of the full-scale bridge module test indicate that the interface shear connection and associated design equations provide effective composite action in the bridge system.

The determination of the dynamic performance of a high-speed (HS) railway bridge is an ever-increasingly topical matter in public transportation networks owing to the broad establishment of ongoing HS railway transportation networks and the implementation of conventional networks for superior operational vehicle velocities. This paper examines the fatigue performance of a welded gusset plate connection of a composite steel I-girder railway bridge under trains moving within a certain range of velocities. The global three-dimensional finite element models (FEMs) are applied to examine the dynamic response of the I-girder composite steel-concrete railway bridge. The natural frequencies of the numerical model of bridge are verified using ambient vibration test results. A local three-dimensional FEM is generated in accordance with critical welded gusset plate connection using the ABAQUS platform. The local submodel is generated congruent with displacement field interpolation. The fatigue performance of a welded joint zone considering critical stress accumulation regions is determined by the hot-spot stress method under resonance conditions due to train passage with varying velocities. Stress cycles are extracted by taking real traffic spectra into account. Fatigue damage is calculated by using Palmgren-Miner’s rule and the rain-flow counting method. The outcomes demonstrate that the bridge is not vulnerable to the forthcoming fatigue failure mode.

The abundance of wood in Brazil combined with the advantages of its use has lead to many studies focusing on optimizing the application of this raw material. In particular, stress-laminated-timber decks are an alternative to conventional building materials for short- to medium-span bridges, and its advantages include low weight and excellent flexibility that enable a high prefabrication rate and quick assembly on site. In order to make the best use of wood, this work studies the behavior of a stress-laminated-timber bridge deck using hardwoods. In brief, three different species were used as laminates, which with the prestress effect made it really difficult to have optimal precision in the numerical analysis, then resulting in higher displacements than those from the tests in almost all comparisons. However, the results of the experimental and numerical displacements followed the same pattern and linearity with reasonable values and low deflections, which demonstrates that the system worked as an orthotropic plate equivalent to the same deck system constructed out of conifers, as widely used in North America for such structures. Further research should be performed with one species only, so that even better results could be found.

Implementing a low-damage design (LDD) approach to improve the seismic behavior of existing RC bridge bents as a retrofit strategy is the main focus of the present study. Experimental and numerical studies were carried out on two 1/4-scale multicolumn RC bridge bents, which had been built based on conventional practice. The LDD approach was implemented by cutting the longitudinal rebars of the columns at both ends to allow rocking, adding unbonded post-tensioned tendons to supply self-centering, and adding two different external devices [buckling-restrained bars and reduced angle sections (RASs)] to provide energy dissipation. Cyclic reversal loading tests were conducted, and the results were compared with a reference nonretrofitted specimen, which was representative of the conventional semiductile design. Nonlinear time-history analyses were performed on calibrated numerical models to study the displacement demands of specimens at design basis earthquake (DBE) and maximum considered earthquake (MCE) events, both far- and near-field. The results showed that the low-damage retrofitted specimens have a better postearthquake condition compared to the reference specimen, particularly in terms of residual drift and damage. The LDD specimens successfully passed the DBE and MCE demands without experiencing failure of cables or dissipation devices.

Bridges located in deep reservoir are exposed to threats from near-fault ground motions. The resilience and economic loss of a highway bridge in deep reservoir under near-fault ground motions require better understanding. This study incorporated the existing resilience and economic loss assessment framework with the effect of post-earthquake underwater repair. The methodology was illustrated to evaluate the seismic performance of an example highway continuous rigid-frame bridge in deep reservoir. The three-dimensional nonlinear numerical model of the example bridge was built with the hydrodynamic added mass estimated by the fluid-structure interaction model. Two types of near-fault ground motions, the forward-directivity and fling-step ground motions, were selected to conduct the nonlinear seismic analyses of the bridge. The fragilities of the piers, bearings, and the bridge system were assessed and resilience and economic loss of the example bridge under different types of near-fault ground motions were evaluated and compared. It can be concluded from the studies that: (1) the peak ground velocity (PGV) is suggested to be taken as the intensity measures of ground motions for the probabilistic seismic demand models of the bridge in deep reservoir; (2) the fling-step ground motions caused larger pier, bearing, and system damage probability, but lower resilience and bigger economic loss than the forward-directivity ground motions; (3) the structural resilience decreases, whereas the economic loss increases with the increasing water level; and (4) the highest water level and the fling-step ground motions result in the worst performance of the example highway bridges in deep reservoir near active faults. The framework not only aids engineers to better understand the seismic performance, but also assists in the decision-making of post-event rehabilitation activities for the highway bridges in deep reservoir.

The trough girder with corrugated steel webs (TGCW), introduced to overcome the inherent limitations of traditional trough bridges, is an innovative steel-concrete composite bridge form consisting of a concrete bottom slab, two corrugated steel webs (CSWs), and a pair of concrete top flanges. The natural vibration characteristics, as the fundamental basis for dynamic analysis, are of great significance for bridge design. However, previous studies were limited to the statistical behaviors of this new bridge form. In this article, a general analytical model applicable to the dynamic behavior of a TGCW was developed based on the energy variation principle and Hamilton theory. Natural frequencies and mode shapes accounting for the coupling effect considering the shear deformation of the TGCW, the shear lag effect of the TGCW bottom flange, and the stiffness correction of CSWs were obtained through the analytical formulas. By comparing the theoretical values and the results of finite element analysis, the correctness of the proposed formulas is verified. Differences in the fundamental frequencies calculated through different analytical formulas are discussed. Sensitivity studies were conducted to address the effects of span length, bottom flange width, CSWs waveform and thickness on the vibration frequencies, and mode shapes of TGCW through finite element analysis.

This paper presents a data set obtained from a monitoring campaign of 15 months on a steel bowstring railway bridge in Leuven, Belgium. In this period, the connections of the diagonals to the bridge deck and the arches were strengthened after the observation of damage. The monitoring consists of measurements of acceleration on the bridge deck and the arches, strain on the bridge deck and the diagonals connecting the bridge deck with the arches, strain on the rails, displacement at the bearings, and temperature and relative humidity. Data is provided for two train passages and six periods of ambient vibration per day. In addition, the evolution of the identified modal characteristics over time is added. The data set is well-suited for the validation of vibration-based structural health monitoring methods, as it includes data for different states of the structure, i.e., before, during, and after the retrofitting.

With the development of new materials and advanced structural analysis, alongside increasing aesthetic requirements, recent years have witnessed a trend toward longer, taller, and lighter footbridges. Different from vehicular bridges, footbridges carry relatively small service loads and are more susceptible to vibrations, due to their lower stiffness, damping, and modal mass. More often than not, vibration serviceability limit state governs the design of footbridges. Providing an accurate evaluation of vibration serviceability performance of existing bridges requires techniques that can include modeling and measurement uncertainties. In this paper, a population-based method called error-domain model falsification (EDMF) is used to assess the vibration serviceability for two pedestrian bridges: Fort Siloso Skywalk located in Singapore and the Dowling Hall Footbridge located at Tufts University in the United States. The unknown properties of the footbridges are identified using the ambient vibration data measured on site. This method is also compared with two other data-interpretation methodologies, that is, residual minimization and traditional Bayesian model updating. The findings show that, through explicitly accounting for measurement and modeling uncertainties, EDMF can provide more accurate identification and prediction results for vibration serviceability assessment of pedestrian bridges.

Bridge structures are subjected to environmental thermal actions, which cause a complex temperature field in bridge structures. This research carried out long-term monitoring of temperature differences in a steel truss bridge with two-layer decks. Big temperature differences existing in the steel truss were revealed and explained using the influence factors of solar motion and two-layer deck shading. The monitoring results show that some temperature differences were notably higher than the specified values in current bridge codes, so appropriate temperature differences for thermal action design were evaluated through probability statistics analysis. The research results show that deck coverage plays an important role in the variation of temperature differences, and there is a big difference between the temperature differences with or without deck shading. Our suggestion is that various types of deck shading should be categorized for more accurate thermal action design in current bridge codes. The steel truss member designed with enough deck coverage can effectively decrease thermal actions. The results of this research will provide meaningful information for thermal action design of steel truss bridges with two-layer deck coverage.